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Animals' learned vocalizations often show high levels of intraspecific variation, and different variants may play different roles in attracting mates and settling territorial disputes. In any animal population with variable vocalizations, certain acoustic variants may be common and others rare. The responses of animals to local versus nonlocal sounds have been well characterized in prior investigations, but few investigations have explored the reactions of animals to songs that are present at different frequencies of occurrence within a population. Using an experimental approach to investigate a breeding population of Savannah sparrows, Passerculus sandwichensis , we tested the responses of territorial male songbirds to playback of locally common songs, locally rare songs and heterospecific songs. Male sparrows showed strong responses to conspecific song but weak responses to heterospecific song. Males showed their strongest responses to locally common songs and weaker responses to locally rare songs. Birds did not appear to discriminate between playback songs based on whether they were of the same song type as their own. We suggest that male Savannah sparrows perceive locally rare songs as weaker threats than locally common songs, similar to birds' reactions to foreign dialects. This could be due to low familiarity with locally rare songs, reduced female preference for locally rare songs, decreased success with territory defence for males singing locally rare songs or other perceived differences between locally rare and locally common songs. Overall, our results suggest that different song types elicit different responses from territorial songbirds, even songs that are found within the same population with different frequencies of occurrence. • Many animals show small-scale geographical variation in vocalizations. • Responses to locally common or locally rare vocalizations are seldom explored. • We used playback to test birds' responses to locally common and locally rare songs. • Savannah sparrows responded more strongly to locally common songs. • We suggest locally common songs are perceived as a stronger threat. [ABSTRACT FROM AUTHOR]

Zebra finch song perception is assumed to primarily involve a high sensitivity to fine spectral features of song elements while other features like element sequence and song duration do not seem to have a notable effect. However, the specific features that zebra finches focus on when identifying or discriminating sounds may not be as fixed as seems to be assumed and might depend on the characteristics of the stimuli. This apparent flexibility in auditory processing, along with the potential salience of differences in song duration for song perception, highlights the need for systematic research on the acoustic parameters that zebra finches can use to differentiate between songs. By employing a Go-Left/Go-Right operant task, we examined whether and how differences in song duration affect zebra finches' relative sensitivity for spectral features and duration in song recognition. Two groups of zebra finches were trained in a Go-Left/Go-Right operant task to discriminate between either two songs with similar durations ('Equal-duration group') or two songs with different durations ('Unequal-duration group'). We assessed to what extent the birds in the two experimental groups attend to the spectral characteristics and the absolute duration of the songs by measuring the responses to test stimuli consisting of spectral modifications or temporal changes. Our results showed that zebra finches use both spectral features and song duration to discriminate between two songs, but the importance of these acoustic parameters depended on whether the songs differed in duration or not. When duration can be used as an additional feature to distinguish two songs, spectral features have a less prominent role. This outcome shows that zebra finches have cognitive flexibility in their attention to different acoustic parameters. • Zebra finches learn to discriminate songs of equal and unequal duration equally fast. • Song duration is used to discriminate songs when their difference is substantial. • Zebra finches prioritize spectral details over spectral envelope for song recognition. • Zebra finches are flexible in the features they use to recognize songs. [ABSTRACT FROM AUTHOR]

Acoustic communication, such as bird song, is vital in animal ecology, facilitating reproduction, feeding, defense, and more. Variation in bird song may result from adaptation to environmental features such as anthropogenic noise. The vocal repertoire of raptors is essentially unstudied, particularly in urban environments. The aim of this work was to describe and quantify the acoustic repertoire of Chimango Caracaras (Milvago chimango) in rural and urban areas in La Pampa Province, Argentina. I recorded 26 1-min sound samples at each of four breeding colonies (one rural and three urban) during the austral reproductive season of 2021–2022. I recorded 241 vocalizations corresponding to nine clearly distinct call types. Two types of calls made up 50.6% and 19.5% of the vocalizations and seven others made up <10.0% each. Three call types had trills (fast repetitive notes). Average percentage of call types differed significantly between the two habitats (P < 0.01), with more trills produced in rural habitats. Average calling rate was 6.6 ± 5.1 calls/min at rural colonies and 10.7 ± 10.7 at urban colonies. The number of different call types produced was 2.1 ± 1.6 types/min at rural colonies and 2.7 ± 1.8 at urban colonies. The greater calling rate of Chimango Caracaras in urban areas may represent an attempt to improve signal effectiveness among the anthropogenic acoustic clutter. La comunicación acústica, como el canto de las aves, es vital en la ecología animal, al facilitar la reproducción, alimentación, defensa y otras actividades. La variación en el canto de las aves puede deberse a la adaptación a características ambientales como el ruido antropogénico. El repertorio vocal de las rapaces ha sido poco estudiado, especialmente en entornos urbanos. El objetivo de este trabajo fue describir y cuantificar el repertorio acústico de Milvago chimango en áreas rurales y urbanas en la provincia de La Pampa, Argentina. Registré 26 muestras de sonido de 1 minuto de duración cada una provenientes de cuatro colonias reproductivas (una rural y tres urbanas) durante la temporada reproductora austral de 2021–2022. Registré 241 vocalizaciones correspondientes a nueve tipos de llamadas claramente distintas. Dos tipos de llamadas representaron el 50.6% y el 19.5% de las vocalizaciones y otras siete representaron <10.0% cada una. Tres tipos de llamadas tuvieron trinos (notas rápidas y repetitivas). Los porcentajes de tipos de llamadas difirieron significativamente entre los dos hábitats (P<0.01), con más trinos producidos en hábitats rurales. La tasa de llamadas fue de 6.6 ± 5.1 llamadas/minuto en colonias rurales y 10.7 ± 10.7 en colonias urbanas. El número de tipos de llamadas diferentes producidas fue de 2.1 ± 1.6 tipos/minuto en colonias rurales y 2.7 ± 1.8 en colonias urbanas. La mayor tasa de llamadas de M. chimango en áreas urbanas puede representar un intento de mejorar la efectividad de la señal ante la distorsión acústica antropogénica. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

A recent reshuffling in the avian phylogeny indicates that New Zealand wrens and songbirds share a close common ancestor with parrots – making New Zealand wrens an excellent group to test for vocal learning. The New Zealand wrens have previously been classified as vocal non-learners, but their vocal learning ability has never been experimentally tested. Here, we explore the potential presence of vocal learning in one species of New Zealand wren, the titipounamu (Acanthisitta chloris). We expose nestlings to synthetic playback stimuli that simulate adult feeding calls and determine whether the nestlings altered their calls after exposure to the playback stimuli. We found that experimental nestlings did not alter their calls towards the playback stimuli. While this indicates that no vocal imitation occurred during the nestling period, other developmental stages should be tested for vocal learning, particularly during the fledgling or first year adult phase. [ABSTRACT FROM AUTHOR]

Animals can learn in real-life scenarios where rewards are often only available when a goal is achieved. This 'distal' or 'sparse' reward problem remains a challenge for conventional reinforcement learning algorithms. Here we investigate an algorithm for learning in such scenarios, inspired by the possibility that axo-axonal gap junction connections, observed in neural circuits with parallel fibres such as the insect mushroom body, could form a resistive network. In such a network, an active node represents the task state, connections between nodes represent state transitions and their connection to actions, and current flow to a target state can guide decision making. Building on evidence that gap junction weights are adaptive, we propose that experience of a task can modulate the connections to form a graph encoding the task structure. We demonstrate that the approach can be used for efficient reinforcement learning under sparse rewards, and discuss whether it is plausible as an account of the insect mushroom body. Author summary: Learning in situations where reward is only rarely encountered is difficult. It is hard to discover the right sequence of actions when most actions, most of the time, provide no apparent progress towards a goal. Inspired by a neural circuit in the insect brain, and using direct electrical connections between neurons as well as synaptic connections, we present a new algorithm for learning. The model represents the states of the world with nodes and an electrical connection between two nodes is strengthened when the two corresponding states occur consecutively. The connections between nodes can also become associated to output actions that correlate with (hence are assumed to cause) transitions between states. When a particular goal is chosen or associated with a reward, for example, the target location in a navigation task, a flow of electrical current through the nodes will find the shortest path from the present state to the goal state and trigger the appropriate actions. [ABSTRACT FROM AUTHOR]

Despite extensive research on avian vocal learning, we still lack a general understanding of how and when this ability evolved in birds. As the closest living relatives of the earliest Passeriformes, the New Zealand wrens (Acanthisitti) hold a key phylogenetic position for furthering our understanding of the evolution of vocal learning because they share a common ancestor with two vocal learners: oscines and parrots. However, the vocal learning abilities of New Zealand wrens remain unexplored. Here, we test for the presence of prerequisite behaviors for vocal learning in one of the two extant species of New Zealand wrens, the rifleman (Acanthisitta chloris). We detect the presence of unique individual vocal signatures and show how these signatures are shaped by social proximity, as demonstrated by group vocal signatures and strong acoustic similarities among distantly related individuals in close social proximity. Further, we reveal that rifleman calls share similar phenotypic variance ratios to those previously reported in the learned vocalizations of the zebra finch, Taeniopygia guttata. Together these findings provide strong evidence that riflemen vocally converge, and though the mechanism still remains to be determined, they may also suggest that this vocal convergence is the result of rudimentary vocal learning abilities. A study suggests that rifleman – one of the two extant species of New Zealand wrens, the most basal Passeriformes in birds – has predispositions for vocal production learning, including group vocal signatures, vocal convergence, and phenotypic variance call ratios similar to vocal learners. [ABSTRACT FROM AUTHOR]

The Yellow Warbler (Setophaga petechia) is a small songbird in the wood-warbler family (Parulidae) that exhibits phenotypic and ecological differences across a widespread distribution and is important to California's riparian habitat conservation. Here, we present a high-quality de novo genome assembly of a vouchered female Yellow Warbler from southern California. Using HiFi long-read and Omni-C proximity sequencing technologies, we generated a 1.22 Gb assembly including 687 scaffolds with a contig N50 of 6.80 Mb, scaffold N50 of 21.18 Mb, and a BUSCO completeness score of 96.0%. This highly contiguous genome assembly provides an essential resource for understanding the history of gene flow, divergence, and local adaptation in Yellow Warblers and can inform conservation management of this charismatic bird species. [ABSTRACT FROM AUTHOR]

As the Arctic becomes increasingly accessible to the resource extraction industry, an understanding of the impacts of infrastructure and anthropogenic disturbance on tundra-nesting avian populations is critical. We conducted breeding bird surveys using point counts and Program for Regional and International Shorebird Monitoring (PRISM) rapid surveys at the Hope Bay Project, an underground gold mine in Nunavut, Canada, from 2007 to 2015. We examined the relationship between abundance of total birds, songbirds, and shorebirds with distance from infrastructure, anthropogenic disturbance (i.e., activity at the mine site), and environmental covariates. Contrary to our predictions, anthropogenic disturbance showed no significant effect on bird abundance for either survey type or bird grouping. However, total bird abundance was associated with distance from infrastructure for both survey methods. A relationship with distance to infrastructure, with variability in influence, was also present for songbird point count data and shorebird PRISM data, but was not significant for songbirds recorded during PRISM surveys. Habitat type played a vital role in determining avian abundance, with PRISM surveys showing that wet lowland ecotypes supported higher bird numbers, whereas point count data revealed a more nuanced habitat association, likely reflecting the specific habitat preferences of different songbirds. Our study highlights the need for strategic planning of industrial development, incorporating comprehensive monitoring and ensuring the protection of preferred Arctic-breeding bird habitats. By aligning development projects with environmental objectives, we can ensure the coexistence of industrial interests and the future of avian populations in the Arctic. [ABSTRACT FROM AUTHOR]

Climate change, management legacies, pest outbreaks, and fire regimes are combining to pose a growing risk of broad-scale loss of forest cover throughout western North America. Already, habitat changes have been linked with declines in numerous bird species; understanding the relative importance of management regimes and habitat structure may be critical to conserving at-risk species. The Olive-sided Flycatcher (Contopus cooperi) is a declining songbird associated with tall, open forests in California's Sierra Nevada, the core of its breeding range, where the management regimes of the National Park Service (NPS) and U.S. Forest Service (USFS) have led to divergent forest conditions over the past century. We combined a landscape-scale passive acoustic monitoring program, the BirdNET animal sound identification algorithm, and single-season occupancy models to explore the relationships between Olive-sided Flycatchers in the Sierra Nevada and both management regimes and fine-scale forest structure. Olive-sided Flycatcher site occupancy increased as canopy cover decreased relative to mean tree diameter, which is consistent with their preference for mature, open forests. These "open forest" conditions were most prevalent on NPS-managed lands, which is consistent with the assumption that the NPS management regime is more faithful to the historical conditions that had supported a larger Olive-sided Flycatcher population than at present. Thus, the support we found for a positive association with USFS-managed lands after controlling for "open forest" suggests that other habitat features are also important. Our results suggest that conservation strategies for Olive-sided Flycatcher breeding habitat should prioritize the protection and generation of open canopies in areas with large trees, as well as the identification of other important habitat features. Prescribed fire, mechanical thinning, and a return of Indigenous forest management practices could help to restore historical forest and fire conditions beneficial to this and other species with similar habitat requirements. Fine-scale alterations to forest structure can be implemented much more rapidly and at much broader scales than the imposition of strict protected status, suggesting that there may be multiple pathways to conservation when species respond to habitat at fine spatial scales. [ABSTRACT FROM AUTHOR]

Population genetic structure is influenced by a combination of contemporary and historical events; however, this structure can be complicated by ongoing gene flow. While it is well known that contemporary hybridization occurs frequently among many closely related species, it often remains uncertain as to which populations are involved in introgression events, and this can be even more difficult to infer when introgression is historical. Here we use restriction-site associated DNA sequencing to look at the level of introgression among four species of songbirds in North America: the black-capped, mountain, boreal, and chestnut-backed chickadee. Samples from both sympatric and allopatric sites across the species' ranges supported limited ongoing mixing among the four species with Bayesian clustering and principal component analyses. In contrast, f4-statistics and admixture graphs revealed extensive historical introgression among geographically structured populations. Almost all historical admixture events were among populations west of the Rocky Mountains, and almost all populations west of the Rocky Mountains, excluding island and coastal populations, showed evidence of historical admixture. The inclusion of all four chickadee species proved crucial in differentiating which species were involved in hybridization events to avoid erroneous conclusions. Taken together, the results suggest a complex pattern of divergence with gene flow. [ABSTRACT FROM AUTHOR]

The cause of recent population declines in some farmland/hedgerow breeding bird species in the UK is related to a lack of cover and food resources in winter. In improved grassland areas some of those declines have been particularly acute and some have been shown to be related to the availability of grass and weed seed in winter. The provision of seed‐bearing crops as part of AES options has been shown to benefit some of these birds. Game crop plots sown on shooting estates for holding and driving gamebirds in autumn and winter have been shown to hold relatively high densities of farmland and wood‐edge birds during the winter. We studied breeding songbirds in hedges in a primarily improved grassland area in the SW of England where there are some large shooting estates that sow relatively large game crop plots (1–5 ha) in the landscape. In this study we found that otherwise similar hedges in terms of size and density near to those winter game crop plots, had between 1.5 and 2 times as many breeding resident songbirds per unit length the following spring compared to hedges further away from game crop plots. This was despite game management in these plots being wound down during February and in many cases, the crops themselves being removed by mid‐March. Hedges within approximately 350 m from game crop plots had more breeding birds. We discuss possible mechanisms and suggest that some passerines preferentially establish breeding territories in hedges near to game crops in late winter. We suggest how to distribute game crop plots to maximise any benefit in an improved grassland landscape. [ABSTRACT FROM AUTHOR]

Song complexity has been identified as one song characteristic important in female choice, whereas its role in male-male interactions is less clear and not much is known which song characteristics are specifically important for territorial defense. In Acrocephalus warblers, males seem to increase song complexity towards females but reduce it during territorial disputes. One possibility to reduce song complexity could be achieved by repeating individual syllables. In this context here we examined the importance of males repeating syllables in male-male interactions. We hypothesis that repeating syllables signals a males general fighting ability, aggressive status or willingness to attack. In a playback experiment we investigated the behavioral response of unmated, territorial Eurasian reed warbler (Acrocephalus scirpaceus) males towards two simultaneously singing intruders whereby the song of the two simulated intruders differs in the degree of syllable repetitions. The response of the territory owner was determined by using several behavioral parameters. Our results revealed that males approached faster and stayed significantly longer near the song with few syllable repetitions. However, the proportion of males approaching the song with high or low syllable repetitions first, as well as the minimal distance to which males approach to the two song types did not differ as well. Thus, the weaker response towards the high repetitive song playback suggests territorial males to be more intimidated by the aggressive nature of that song type. [ABSTRACT FROM AUTHOR]

In species with resource-defense mating systems (such as most temperate-breeding songbirds), male dispersal is often considered to be limited in both frequency and spatial extent. When dispersal occurs within a breeding season, the favored explanation is ecological resource tracking. In contrast, movements of male birds associated with temporary emigration, such as polyterritoriality (i.e., defense of an additional location after attracting a female in the initial territory), are usually attributed to mate searching. We suggest that male dispersal and polyterritoriality are functionally related and that mate searching may be a unifying hypothesis for predicting the within-season movements of male songbirds. Here, we test three key predictions derived from this hypothesis in Wood Warblers (Phylloscopus sibilatrix). We collected data on the spatial behavior of 107 males between 2017 and 2019 and related male movements to a new territory (in both a dispersal and a polyterritorial context) to mating potential in the current territory. Most males dispersed from their territories within days or weeks after failing to attract a female, despite occupying territories in apparently suitable habitat. Probability of polyterritoriality by paired males increased after the peak fertile period of their mate. Males never dispersed following nest predation if the female remained to renest. Thus, our data are consistent with the hypothesis that both movement types are functionally related to mate searching. [ABSTRACT FROM AUTHOR]

Autonomous sensors provide opportunities to observe organisms across spatial and temporal scales that humans cannot directly observe. By processing large data streams from autonomous sensors with deep learning methods, researchers can make novel and important natural history discoveries. In this study, we combine automated acoustic monitoring with deep learning models to observe breeding-associated activity in the endangered Sierra Nevada yellow-legged frog (Rana sierrae), a behavior that current surveys do not measure. By deploying inexpensive hydrophones and developing a deep learning model to recognize breeding-associated vocalizations, we discover three undocumented R. sierrae vocalization types and find an unexpected temporal pattern of nocturnal breeding-associated vocal activity. This study exemplifies how the combination of autonomous sensor data and deep learning can shed new light on species' natural history, especially during times or in locations where human observation is limited or impossible. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) widely affects wildlife by blurring light‐dark differences, including transitions such as sunrise and sunset, thereby affecting regulation of diel rhythms. As a result, activity onsets in many wild diurnal songbirds advance under ALAN. From chronobiological studies, it is known that the direction and strength of the response to light depends on when during the night exposure takes place. However, these experiments are mostly done under continuous light conditions, when animals have free‐running rhythms. It remains unclear whether phase‐dependence also holds in entrained, wild songbirds; i.e., does the effect of ALAN on activity patterns differ between exposure in the morning compared to the evening? This information is essential to assess the effects of mitigation measures by limiting ALAN to selected times of the night. We exposed incubating great tits (Parus major) inside the nest‐box to 4 h of dim light, of which 1 h overlapped with dawn before sunrise or dusk after sunset. We found a small advancing effect of morning‐light on activity onset and of evening‐light on offset compared to dark controls but not vice versa. Breeding success and chick condition were unaffected by the light treatments. However, light‐treated females had lower weights 9–18 days after the end of the treatment compared to the controls, independent of whether ALAN occurred in the morning or the evening, indicating possible costs of ALAN. Despite the weak behavioral response, ALAN might have affected the females' circadian clock or physiology resulting in lower body condition. Research Highlights: Part‐night lighting alters natural shifts in incubation activity patterns. Thus, onset advanced by light in the early morning and offset by light in the early evening compared to dark controls, and led to lower body weights. [ABSTRACT FROM AUTHOR]

Complex skills like speech and dance are composed of ordered sequences of simpler elements, but the neuronal basis for the syntactic ordering of actions is poorly understood. Birdsong is a learned vocal behavior composed of syntactically ordered syllables, controlled in part by the songbird premotor nucleus HVC (proper name). Here, we test whether one of HVC's recurrent inputs, mMAN (medial magnocellular nucleus of the anterior nidopallium), contributes to sequencing in adult male Bengalese finches (Lonchura striata domestica). Bengalese finch song includes several patterns: (1) chunks, comprising stereotyped syllable sequences; (2) branch points, where a given syllable can be followed probabilistically by multiple syllables; and (3) repeat phrases, where individual syllables are repeated variable numbers of times. We found that following bilateral lesions of mMAN, acoustic structure of syllables remained largely intact, but sequencing became more variable, as evidenced by 'breaks' in previously stereotyped chunks, increased uncertainty at branch points, and increased variability in repeat numbers. Our results show that mMAN contributes to the variable sequencing of vocal elements in Bengalese finch song and demonstrate the influence of recurrent projections to HVC. Furthermore, they highlight the utility of species with complex syntax in investigating neuronal control of ordered sequences. [ABSTRACT FROM AUTHOR]

Urban expansion has increased pollution, including both physical (e.g., exhaust, litter) and sensory (e.g., anthropogenic noise) components. Urban avian species tend to increase the frequency and/or amplitude of songs to reduce masking by low-frequency noise. Nevertheless, song propagation to the receiver can also be constrained by the environment. We know relatively little about how this propagation may be altered across species that (1) vary in song complexity and (2) inhabit areas along an urbanization gradient. We investigated differences in song amplitude, attenuation, and active space, or the maximum distance a receiver can detect a signal, in two human-commensal species: the house sparrow (Passer domesticus) and house finch (Haemorhous mexicanus). We described urbanization both discretely and quantitatively to investigate the habitat characteristics most responsible for propagation changes. We found mixed support for our hypothesis of urban-specific degradation of songs. Urban songs propagated with higher amplitude; however, urban song fidelity was species-specific and showed lowered active space for urban house finch songs. Taken together, our results suggest that urban environments may constrain the propagation of vocal signals in species-specific manners. Ultimately, this has implications for the ability of urban birds to communicate with potential mates or kin. [ABSTRACT FROM AUTHOR]

The auditory sensitivity of a small songbird, the red-cheeked cordon bleu, was measured using the standard methods of animal psychophysics. Hearing in cordon bleus is similar to other small passerines with best hearing in the frequency region from 2 to 4 kHz and sensitivity declining at the rate of about 10 dB/octave below 2 kHz and about 35 dB/octave as frequency increases from 4 to 9 kHz. While critical ratios are similar to other songbirds, the long-term average power spectrum of cordon bleu song falls above the frequency of best hearing in this species. [ABSTRACT FROM AUTHOR]

Many animals rely on photoperiodic and non-photoperiodic environmental cues to gather information and appropriately time life-history stages across the annual cycle, such as reproduction, molt, and migration. Here, we experimentally demonstrate that the reproductive physiology, but not migratory behavior, of captive Pine Siskins (Spinus pinus) responds to both food and social cues during the spring migratory-breeding period. Pine Siskins are a nomadic finch with a highly flexible breeding schedule and, in the spring, free-living Pine Siskins can wander large geographic areas and opportunistically breed. To understand the importance of non-photoperiodic cues to the migratory-breeding transition, we maintained individually housed birds on either a standard or enriched diet in the presence of group-housed heterospecifics or conspecifics experiencing either the standard or enriched diet type. We measured body condition and reproductive development of all Pine Siskins and, among individually housed Pine Siskins, quantified nocturnal migratory restlessness. In group-housed birds, the enriched diet caused increases in body condition and, among females, promoted reproductive development. Among individually housed birds, female reproductive development differed between treatment groups, whereas male reproductive development did not. Specifically, individually housed females showed greater reproductive development when presented with conspecifics compared to heterospecifics. The highest rate of female reproductive development, however, was observed among individually housed females provided the enriched diet and maintained with group-housed conspecifics on an enriched diet. Changes in nocturnal migratory restlessness did not vary by treatment group or sex. By manipulating both the physical and social environment, this study demonstrates how multiple environmental cues can affect the timing of transitions between life-history stages with differential responses between sexes and between migratory and reproductive systems. [ABSTRACT FROM AUTHOR]

We assessed correlations between speciation rate and bill morphology in an ecologically diverse and continental-scale songbird radiation, the tanagers (Thraupidae). Our analyses showed that bill size, shape, and their evolutionary rates are not correlated with speciation rate. However, we did find evidence that each axis of variation in bill morphology diversifies at speciation events interspersed with periods of gradual evolution, consistent with a punctuated equilibrium model of character change. To determine correlations, we incorporated a time-calibrated molecular phylogeny and high-resolution three-dimensional surface scans of bill structure from museum study skins. Overall, our findings suggest that bill size and shape diversify in association with the speciation process, but not through any effect on the rate of speciation. Previous studies have shown other traits, such as song, ecological niche, and plumage do influence speciation and, ultimately, species richness in tanagers. [ABSTRACT FROM AUTHOR]

Predation is well known to have substantial effects on behaviour and fitness in many animals. In songbirds, nest predation is rarely observed directly, so that research focusses primarily on the consequences of predation and less on the behaviour of the predator. Here, we report predation data in a zebra finch (Taeniopygia catanosis) nest box population, highlighting a 22‐min‐long sequence, captured on video, of a sand goanna (Varanus gouldii) predating a zebra finch nest in the wild. This monitor lizard appeared to be extremely persistent with climbing and jumping up to the next box nine times, including three successive unsuccessful attempts that lead to a change in approach strategy. It removed all six nestlings from the nest box during those repeated approaches and consumed them. In combination with overall high predation rates in the study population we document here, the findings highlight the role that a single predator species can have on nest success and, thus potentially also breeding decisions and social organisation of the prey population. Specifically so in a species like the zebra finch which synchronises reproductive attempts through the use of social information acquired through nest inspections and which uses social hotspots where they could gather information on changes in local social composition due to the individualised signals they use. [ABSTRACT FROM AUTHOR]

Simple Summary: The Atlantic herring is one of many migratory fish that may use the geomagnetic field to navigate on its annual migration. The exact mechanism used for detecting the geomagnetic field in fish is still an open discussion, and the two main theories on magnetic sensing in animals are in the main focus: magnetite-based or radical pair-based. Here, we explore whether the cryptochrome 4 protein of fish would be able to carry out the necessary electron transfer activation to create a radical pair to be used for magnetic sensing. Marine fish migrate long distances up to hundreds or even thousands of kilometers for various reasons that include seasonal dependencies, feeding, or reproduction. The ability to perceive the geomagnetic field, called magnetoreception, is one of the many mechanisms allowing some fish to navigate reliably in the aquatic realm. While it is believed that the photoreceptor protein cryptochrome 4 (Cry4) is the key component for the radical pair-based magnetoreception mechanism in night migratory songbirds, the Cry4 mechanism in fish is still largely unexplored. The present study aims to investigate properties of the fish Cry4 protein in order to understand the potential involvement in a radical pair-based magnetoreception. Specifically, a computationally reconstructed atomistic model of Cry4 from the Atlantic herring (Clupea harengus) was studied employing classical molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) methods to investigate internal electron transfers and the radical pair formation. The QM/MM simulations reveal that electron transfers occur similarly to those found experimentally and computationally in Cry4 from European robin (Erithacus rubecula). It is therefore plausible that the investigated Atlantic herring Cry4 has the physical and chemical properties to form radical pairs that in turn could provide fish with a radical pair-based magnetic field compass sensor. [ABSTRACT FROM AUTHOR]

Modification of ecosystems as a consequence of urbanisation alters natural habitat structures and soundscapes, creating constraints for vocal communication in animals. Birds are able to adjust their vocalisation to the prevailing acoustic features of their habitat. As such, their sounds have been shown to reflect the level of anthropogenic disturbances across landscapes. While the effect of a single anthropogenic disturbance like ambient noise on birds' vocal communication is widely investigated, the combined effects of various disturbances remain less explored. We tested single and combined effects of anthropogenic noise and urban physical structures on the vocalisations of two African passerines, the Common Bulbul Pycnonotus barbatus and Northern Grey-headed Sparrow Passer griseus. We predicted that (i) both species would increase the minimum frequency of their vocalisation to avoid masking by ambient noise, (ii) both species would decrease their maximum frequency to evade distortion by physical structures, (iii) the two urban components would have a significant combined effect on the vocalisations, and (iv) the change in minimum or maximum frequency will lead to a corresponding change in the vocalisation bandwidth. For the Common Bulbul, the minimum frequency increased significantly as the ambient noise level increased, but the maximum frequency did not change in response to urban physical structures. For the Northern Grey-headed Sparrow, the minimum frequency did not show a response to ambient noise, but the maximum frequency decreased significantly as physical structures and ambient noise increased. We did not find any evidence for a combined effect of urban physical structures and ambient noise on the vocal adjustment of either species. A change in either the minimum or maximum frequency resulted in a corresponding change in the vocalisation bandwidth of each species. Our findings highlight how the same vocalisation traits of different songbird species can be affected differently by novel selective pressures in acoustic communication that arise in urban environments. [ABSTRACT FROM AUTHOR]

Migratory divides, hybrid zones between populations that use different seasonal migration routes, are hypothesised to contribute to speciation. Specifically, relative to parental species, hybrids at divides are predicted to exhibit (1) intermediate migratory behaviour and (2) reduced fitness as a result. We provide the first direct test of the second prediction here with one of the largest existing avian tracking datasets, leveraging a divide between Swainson's thrushes where the first prediction is supported. Using detection rates as a proxy for survival, our results supported the migratory divide hypothesis with lower survival rates for hybrids than parental forms. This finding was juvenile‐specific (vs. adults), suggesting selection against hybrids is stronger earlier in life. Reduced hybrid survival was not explained by selection against intermediate phenotypes or negative interactions among phenotypes. Additional work connecting specific features of migration is needed, but these patterns provide strong support for migration as an ecological driver of speciation. [ABSTRACT FROM AUTHOR]

Anthropogenic noise is one of the fastest growing, globally widespread pollutants, affecting countless species worldwide. Despite accumulating evidence of the negative impacts of wind turbines on wildlife, little is known about how the noise they generate affects ecological systems. Songbirds may be susceptible to noise pollution due to their reliance on vocal communication and thus, in this field study, we examined how songbirds are affected by wind turbine noise. We broadcasted noise produced by one wind turbine in a migratory stopover site during the nonbreeding season. Throughout the study, we repeatedly monitored the acoustic environment and songbird community before, during, and after the noise treatments with passive acoustic monitoring and mist netting. We employed generalized linear mixed effects models to assess the impact of experimental noise treatment on birds behavior and likelihood ratio tests to compare models with variables of interest with null models. The daily number of birds in the presence of wind turbine noise decreased by approximately 30% compared with the before and after phases. This reduction had a significant spatial pattern; the largest decrease was closer to the speaker and on its downwind side, fitting measured sound propagation. Although we found no impact on species diversity, two out of three most common species showed clear avoidance behavior: 45% and 36% decrease in abundance for the lesser whitethroat (Sylvia curruca) and Sardinian warbler (Sylvia melanocephala momus), respectively. In the after phase, there were lingering effects on the lesser whitethroat. The age structure of the lesser whitethroat population was affected because only juvenile birds showed avoidance behavior. No difference in avoidance extent was found between migratory and nonmigratory species, but the impacts of displacement on migrants during stopover are especially troubling from a conservation perspective. Our results stress the need to address the impacts of noise pollution on wildlife when planning noise‐generating infrastructures, such as wind turbines, to allow for sustainable development without threatening already declining songbird populations. [ABSTRACT FROM AUTHOR]

Many animals exhibit contrast between their dorsal coloration and their ventral coloration. If selection acts differently on dorsal versus ventral coloration, ancestral covariance between these traits should break down, eventually leading to independent modules of trait evolution. Here, we compare the evolution of feather color across body regions for a clade of Australasian songbirds (Meliphagoidea). We find evidence for three modules of covarying color regions. Among these modules, ventral feathers evolve with high lability, evolving at three times the rate of dorsal plumage and 20 times the rate of flight feathers. While both dorsal plumage and ventral plumage are darker in areas with more precipitation and vegetation, we find that dorsal plumage is twice as similar to colors in satellite photos of background substrates. Overall, differential selection on ventral and dorsal colors likely maintains these as distinct modules over evolutionary timescales—a novel explanation for dorsoventral contrast in pigmentation. [ABSTRACT FROM AUTHOR]

Individual variation in the timing of activities is increasingly being reported for a wide variety of species, often measured as the timing of activity onset in the morning. However, so far, the adaptive significance of consistent variation in temporal phenotypes (i.e. the chronotype) remains largely elusive. Potentially, differences in timing of activities may arise as a result of competition among individuals for resources. Less aggressive individuals may try to avoid competition by becoming active earlier during the day when other individuals are still inactive, leading to a positive correlation between chronotype and aggressive personality type (i.e. a behavioural syndrome). To investigate this, we assessed the chronotype of female great tits, Parus major , by measuring emergence time from the nestbox in the morning and experimentally tested their levels of same-sex aggression through simulated territorial intrusion tests. Contradicting our initial hypothesis, consistently more aggressive females became active earlier during the day compared to less aggressive females, which could be caused by shared underlying mechanisms, like pleiotropic effects of sex hormones or gene pleiotropy, which potentially impose constraints on the independent evolution of both traits. Surprisingly, on the within-individual level we found an opposing correlation between emergence time and aggression. Our findings highlight the need for further investigations into the interplay between chronotype and aggression that take the underlying mechanisms into account in order to understand the adaptive significance of this trait association. • We explored the relationship between chronotype and aggression in female great tits. • Females starting activity earlier in the morning had a more aggressive personality. • This observation suggested the presence of a behavioural syndrome. • Intriguingly, we found an opposite correlation within individuals. • These findings may have implications for the evolutionary potential of both traits. [ABSTRACT FROM AUTHOR]

Motivation to seek social interactions is inherent to all social species. For instance, even with risk of disease transmission in a recent pandemic, humans sought out frequent in-person social interactions. In other social animals, socialization can be prioritized even over water or food consumption. Zebra finches, Taeniopygia guttata , are highly gregarious songbirds widely used in behavioural and physiological research. Songbirds, like humans, are vocal learners during development, which rely on intense auditory learning. Aside from supporting song learning, auditory learning further supports individual identification, mate choice and outcome associations in songbirds. To study auditory learning in a laboratory setting, studies often employ operant paradigms with food restriction and reinforcement and require complete social isolation, which can result in stress and other unintended physiological consequences for social species. Thus, in this work, we designed an operant behavioural method leveraging the sociality of zebra finches for goal-directed behaviours. Our approach relies on visual social reinforcement, without depriving the animals of food or social contact. Using this task, we found that visual social reinforcement was a strong motivational drive for operant behaviour. Motivation was sensitive to familiarity towards the stimulus animal and higher when engaging with a familiar versus a novel individual. We further show that this tool can be used to assess auditory discrimination learning using either songs or synthetic pure tones as stimuli. As birds gained experience in the task, they developed a strategy to maximize reward acquisition in spite of receiving more punishment, i.e. liberal response bias. Our operant paradigm provides an alternative to tasks using food reinforcement and could be applied to a variety of highly social species, such as rodents and nonhuman primates. • We used a novel social reward-based operant task for zebra finches. • Birds were more motivated to obtain access to familiar over novel conspecifics. • Social motivation reinforced auditory discrimination learning in a Go/No-go task. • Birds with more experience in the Go/No-go task developed liberal response bias. [ABSTRACT FROM AUTHOR]

Dialects have been described as geographical variations of vocal signals in several taxa such as humans, cetaceans, bats and birds. Many playback studies have focused on dialect perception by territorial birds, mainly reporting a stronger aggressiveness towards local dialects in comparison to foreign ones. However, exploration of the influence of several methodological factors is lacking, and very few studies have focused on species displaying microdialects (covering distances under 2 km). We investigated these issues in a migratory population of a territorial songbird, the black redstart, Phoenicurus ochruros. In this species only males sing to defend their territories, and their distribution leads to several small groups of neighbours with a relatively high level of song sharing within each group. Using a playback experiment, we tested whether males were able to discriminate between the local and a foreign microdialect, while testing for the effects of their age class, the initial distance to the speaker, the relative acoustic similarity between the playback songs and songs of the tested birds and the order of the stimuli. We broadcast two acoustic stimuli (foreign and local microdialect) from unfamiliar individuals to 26 territorial males, during two breeding seasons. In line with our predictions, males showed a stronger response towards the local microdialect, spending more time in proximity to the speaker, in agreement with the escalation chain of aggression. Our results conformed to the previously reported trend in wide-spanning dialect species. We also showed that both the vocal response and the approach behaviours were influenced by the distance of tested males from the speaker at the beginning of the experiment. Males that were further from the sound source tended to sing rather than approach. More studies are needed to get a better understanding of discrimination abilities and their functions in microdialect species. • Males were more aggressive towards the local microdialect than the foreign one. • Similarity between the stimuli and the focal males' song predicts aggression level. • Vocal response was influenced by the males' initial distance from the speaker. • Approach response was influenced by the males' initial distance from the speaker. [ABSTRACT FROM AUTHOR]

Song in oscine birds is learned across generations, and aspects of the song-learning process parallel genetic transmission: variation can be introduced into both cultural and genetic traits via copy error, and both types of traits are subject to drift and selective pressure. Similarly to allele frequencies in population genetics, observing frequencies of birdsong features can improve our understanding of cultural transmission and evolution. Uniquely, community science databases of birdsong provide rich spatiotemporal data with untapped potential to evaluate cultural evolution in songbirds. Here we use both community science and field study recordings of chipping sparrows, Spizella passerina , to examine trends across nearly seven decades of song. We found that some syllable types tended to persist in the population for much longer than others. Persistent songs tended to contain more syllables of shorter duration than songs that were observed across fewer years. To draw inferences about the effects of learning biases on chipping sparrow syllables, we constructed a spatially explicit agent-based model of song learning. By comparing our empirical analysis to simulated song distributions using three different song-learning strategies (neutral transmission, conformity bias and directional selection), we suggest that chipping sparrows are unlikely to select tutors neutrally or with a conformity bias and that they learn their songs with a remarkably low copy error rate. • Computational models can complement data from community science. • We model chipping sparrow song learning and compare results to historical recordings. • Chipping sparrows likely select which song they learn and sing as adults. • Their choice of which song they learn may depend on a quality of that song. • Short- and long-lived songs (recorded in 1 vs ≥50 years) have different properties. [ABSTRACT FROM AUTHOR]

Night-migrating songbirds utilize the Earth's magnetic field to help navigate to and from their breeding sites each year. A region of the avian forebrain called Cluster N has been shown to be activated during night migratory behavior and it has been implicated in processing geomagnetic information. Previous studies with night-migratory European songbirds have shown that neuronal activity at Cluster N is higher at night than during the day. Comparable work in North American migrants has only been performed in one species of swallows, so extension of examination for Cluster N in other migratory birds is needed. In addition, it is unclear if Cluster N activation is lateralized and the full extent of its boundaries in the forebrain have yet to be described. We used sensory-driven gene expression based on ZENK and the Swainson's thrush, a night-migratory North American songbird, to fill these knowledge gaps. We found elevated levels of gene expression in night- vs. day-active thrushes and no evidence for lateralization in this region. We further examined the anatomical extent of neural activation in the forebrain using 3D reconstruction topology. Our findings demonstrate that Swainson's thrushes possess an extensive bilateral night-activated Cluster N region in the forebrain similar to other European avian species, suggesting that Cluster N is highly conserved in nocturnal migrants. [ABSTRACT FROM AUTHOR]

Simple Summary: Saltator similis is a species of songbird that is a victim of illegal trafficking, native to Brazilian forests, and kept in captivity. Nine fecal samples were collected from free-living birds, and nine birds in captivity were sampled. Total bacterial DNA was obtained from the feces and sequenced. The most predominant phyla were analyzed and compared. The bacterial genera "Candidatus Arthromitus", Acinetobacter, Kocuria, and Paracoccus were identified exclusively in animals living in captivity, which may be potential biomarkers associated with birds in captive environments and under a restricted diet and stressful lifestyle. This study presents the first description of the fecal bacterial community composition of S. similis living in two different lifestyles. Finally, our results suggest that the lifestyle of S. similis birds significantly impacts the composition of their fecal microbiota. The results can bring about new discussions about the management and health of captive birds. The microbiota's alteration is an adaptive mechanism observed in wild animals facing high selection pressure, especially in captive environments. The objective of this study is to compare and predict the potential impact of habitat on the fecal bacterial community of Saltator similis, a songbird species that is a victim of illegal trafficking, living in two distinct habitats: wild and captivity. Nine wild and nine captive S. similis were sampled, and total bacterial DNA was obtained from the feces. Each DNA sample was employed to the amplification of the V4 region of the 16S rDNA following high-throughput sequencing. The most predominant phyla in all songbirds, irrespective of habitat, were Firmicutes, Bacteroidota, Proteobacteria, and Actinobacteriota. Interestingly, a microbiota profile (phylogenetic and abundance relationship) related to habitat was identified. The genera "Candidatus Arthromitus", Acinetobacter, Kocuria, and Paracoccus were exclusively identified in animals living in captivity, which can be a potential biomarker associated with birds in captive environments. This study presents the first description of the fecal bacterial community composition of S. similis living two different lifestyles. Finally, our results suggest that the lifestyle of S. similis birds significantly impacts the composition of the fecal microbiota. The animals living in captivity showed dysbiosis in the microbiota, with some bacteria genera being indicated as biological markers of environmental behavior. Thus, the present research provides a new concept of life quality measure for songbirds. [ABSTRACT FROM AUTHOR]

Juvenile male zebra finches (Taeniopygia guttata) must be exposed to an adult tutor during a sensitive period to develop normal adult song. The pre-motor nucleus HVC (acronym used as a proper name), plays a critical role in song learning and production (cf. Broca's area in humans). In the human brain, left-side hemispheric dominance in some language regions is positively correlated with proficiency in linguistic skills. However, it is unclear whether this pattern depends upon language learning, develops with normal maturation of the brain, or is the result of pre-existing functional asymmetries. In juvenile zebra finches, even though both left and right HVC contribute to song production, baseline molecular activity in HVC is left-dominant. To test if HVC exhibits hemispheric dominance prior to song learning, we raised juvenile males in isolation from adult song and measured neuronal activity in the left and right HVC upon first exposure to an auditory stimulus. Activity in the HVC was measured using the immediate early gene (IEG) zenk (acronym for zif-268, egr-1, NGFI-a, and krox-24) as a marker for neuronal activity. We found that neuronal activity in the HVC of juvenile male zebra finches is not lateralized when raised in the absence of adult song, while normally-reared juvenile birds are left-dominant. These findings show that there is no pre-existing asymmetry in the HVC prior to song exposure, suggesting that lateralization of the song system depends on learning through early exposure to adult song and subsequent song-imitation practice. [ABSTRACT FROM AUTHOR]

From endangered Hawaiian songbirds to dolphins deafened by Navy sonar to a neglected horse named Justice, nonhuman animals increasingly appear as plaintiffs in lawsuits alleging their subjection to extinction, abuse, and other injustices. These cases are far more than mere novelties or publicity stunts; they raise important jurisprudential questions about what it means to be a plaintiff seeking relief. As we learn more about the richness and diversity of nonhuman life, our legal system will have to rethink its exclusions to meet the demands of interspecies justice. Drawing on a diverse body of philosophical, jurisprudential, and scientific scholarship, this Article is the first to offer a comprehensive theory of plaintiffhood and apply it to nonhuman animals. It defends the plaintiffhood of animals by articulating the conceptual foundations of the figure of the plaintiff as an entity who complains about injustice, mourns death, and laments the mistreatment of herself and others. Developments in the study of animal behavior and cognitive ethology have demonstrated these features in animals—including inequity aversion in monkeys, grief in elephants, and resistance to exploitation amongst many other species. As sentient and plaintive beings, animals are conceptually situated to serve as plaintiffs. In addition to describing the conceptual contours of plaintiffhood, this Article identifies plaintiffhood’s jurisprudential requirements and then analyzes whether animals can meet these expectations. Plaintiffs must be legal persons, possess legal rights, have legal capacity (or a representative to defend their interests), and have standing to pursue their claims. Through an engagement with legal theory and case law, this Article argues that animals are legal persons with legal rights that representatives can enforce in cases where animals have suffered the kinds of injuries that confer standing. As such, it concludes that animals are entitled to be plaintiffs in lawsuits. To deny them the ability to enforce their rights in court is unjustly anthropocentric. [ABSTRACT FROM AUTHOR]

In temperate regions, the annual pattern of spring onset can be envisioned as a 'green wave' of emerging vegetation that moves across continents from low to high latitudes, signifying increasing food availability for consumers.Many herbivorous migrants 'surf' such resource waves, timing their movements to exploit peak vegetation resources in early spring. Although less well studied at the individual level, secondary consumers such as insectivorous songbirds can track vegetation phenology during migration as well.We hypothesized that four species of ground‐foraging songbirds in eastern North America—two warblers and two thrushes—time their spring migrations to coincide with later phases of vegetation phenology, corresponding to increased arthropod prey, and predicted they would match their migration rate to the green wave but trail behind it rather than surfing its leading edge.We further hypothesized that the rate at which spring onset progresses across the continent influences bird migration rates, such that individuals adjust migration timing within North America to phenological conditions they experience en route.To test our hypotheses, we used a continent‐wide automated radio telemetry network to track individual songbirds on spring migration between the U.S. Gulf Coast region and northern locations closer to their breeding grounds.We measured vegetation phenology using two metrics of spring onset, the spring index first leaf date and the normalized difference vegetation index (NDVI), then calculated the rate and timing of spring onset relative to bird detections.All individuals arrived in the southeastern United States well after local spring onset. Counter to our expectations, we found that songbirds exhibited a 'catching up' pattern: Individuals migrated faster than the green wave of spring onset, effectively closing in on the start of spring as they approached breeding areas.While surfing of resource waves is a well‐documented migration strategy for herbivorous waterfowl and ungulates, individual songbirds in our study migrated faster than the green wave and increasingly caught up to its leading edge en route.Consequently, songbirds experience a range of vegetation phenophases while migrating through North America, suggesting flexibility in their capacity to exploit variable resources in spring. [ABSTRACT FROM AUTHOR]

Acoustic signals are of critical importance to songbirds which rely on them for mate attraction and territorial defence. Interference caused by sounds that overlap in frequency and time can disturb or mask signal detection. While species differ in their song spectral properties, duration and composition, the limited acoustic space may lead to evolution of behavioural strategies aimed at minimizing competition. Using playback experiments we tested whether tropical forest songbirds use temporal or spectral avoidance to reduce competition for acoustic space. We focused on two species with different song spectral ranges: green-backed camaroptera, Camaroptera brachyura , with a broad-spectrum song, and scaly-breasted illadopsis, Illadopsis albipectus , which produces a narrow-spectrum song. We found that scaly-breasted illadopsis avoided both temporal and spectral overlap. By contrast, in green-backed camaroptera, there was no difference in the number of songs produced between the periods of silence and noise. However, when we varied the frequency of the noise, green-backed camaroptera increased the song rate during the playbacks of noise with maximal spectral overlap, suggesting increasing signal redundancy. Our results show that competition avoidance strategies may be species specific and could be related to the spectral frequency range of the species. • We presented two tropical songbird species with noise matching their song frequency. • Species with narrow-spectrum songs avoided the noise both temporally and spectrally. • Species with wide-spectrum songs showed no temporal or spectral avoidance. • Species with wide-spectrum songs increased signal redundancy in competing noise. • Competition avoidance strategies in ecologically similar bird species can differ. [ABSTRACT FROM AUTHOR]

Simple Summary: Urban noise imposes significant challenges for the acoustic communication of birds that are able to survive inside cities. Birds sing most intensely during two periods of the day called dawn and dusk choruses, and although various responses to the urbanization of dawn songs have been reported, very little attention was paid to the dusk chorus. Our objective is to evaluate in urban and non-urban populations of the Chiguanco Thrush (Turdus chiguanco), a very common bird in the city of La Paz (Bolivia) if there are differences between the songs of both choruses, and if these variations are altered by urbanization. Our results show that the loudness, frequency range and number of songs per individual are greater in the dawn chorus and that urban individuals must increase the frequency and loudness of their songs in both choruses to cope with urban noise. Urban Chiguanco Thrushes even produce less than half as many songs per individual compared to non-urban individuals, probably due to the high cost of increasing loudness and frequency. If wild birds are forced to modify their songs so much within the city, this should alert us to the possible negative effects of urban noise on human health. Urbanization is one of the more important phenomena affecting biodiversity in the Anthropocene. Some organisms can cope with urban challenges, and changes in birds' acoustic communication have been widely studied. Although changes in the timing of the daily organization of acoustic communication have been previously reported, there is a significant gap regarding possible variations in song structure between dawn and dusk choruses. Considering that urbanization imposes different soundscapes for dawn and dusk choruses, we postulate two hypotheses: (i) there are variations in song parameters between dawn and dusk choruses, and (ii) such parameters within the city will vary in response to urban noise. We studied urban and extra-urban populations of Chiguanco Thrush in La Paz, Bolivia, measuring in dawn and dusk choruses: song length; song sound pressure level; minimum, maximum, range and dominant frequency; and the number of songs per individual. The results support our two hypotheses: there were more songs, and songs were louder and had larger band widths at dawn than at dusk in urban and extra-urban populations. Urban Chiguanco Thrushes sing less, the frequency of the entire song rises, and the amplitude increases as compared with extra-urban Chiguanco Thrushes. Understanding variations between dawn and dusk choruses could allow for a better interpretation of how some bird species cope with urban challenges. [ABSTRACT FROM AUTHOR]

Determining the drivers and mechanisms for first year survival of migratory songbirds has been an understudied area in population dynamics due to the difficulty in tracking juveniles once they have dispersed from the natal site. With the advancement in miniaturization of radio-tags (battery life ~400 days) and the development of the Motus Wildlife Tracking System, we tracked 189 Wood Thrush (Hylocichla mustelina) nestlings through independence and to fall migration departure, and their return the following spring. Natal forest fragment size and landscape forest cover (at different spatial scales) were not strong predictors of fledgling, pre-migration, or apparent annual survival; and onset of fall migration was best predicted by fledge date but not natal fragment size. Survival probability was lowest the first 16 days post-fledging (70%, or 0.86 weekly survival probability), very high for juveniles as they explored the landscape prior to fall migration (89%, or 0.99 weekly survival probability) and low during their first migration and wintering season (26%, or 0.95 weekly survival probability). To our knowledge, this is the first study to directly estimate annual apparent juvenile survival in a migratory songbird using year-round radio-tracking. Our study suggests that small forest fragments are important for the conservation for forest songbirds because they can support high survival of juveniles. [ABSTRACT FROM AUTHOR]

Predator removal comprises one management strategy to increase the reproductive success of a prey species of concern, particularly within human-altered landscapes. The efficacy of such an approach, however, depends partly on the extent to which predation risk is additive or compensatory, which remains unknown for many systems. We experimentally reduced the local abundance of deer mice (Peromyscus maniculatus), a primary nest predator of three sagebrush-obligate songbirds--Brewer's Sparrow (Spizella breweri), Sagebrush Sparrow (Artemisiospiza nevadensis), and Sage Thrasher (Oreoscoptus montanus)--during May to August 2019 in western Wyoming, USA, to assess whether nest predation risk was additive or compensatory, and whether nest predator removal could comprise a potentially effective management tool. Deer mouse removal did not affect the daily nest survival of songbirds between experimental and control plots, despite a reduction of 68%--85% in deer mouse abundance within treatment areas. Therefore, nest predation in this system likely operated in a compensatory way, in which deer mice that escaped removal, new immigrants, or other species of nest predator maintained similar levels of nest predation risk regardless of the prevalence of a primary predator. We caution that predator removal may not be an effective management tool in systems that lack barriers to predator immigration or have several alternative species of predators, even when a single species typically is responsible for the majority of predation events. [ABSTRACT FROM AUTHOR]

Motor performance is monitored continuously by specialized brain circuits and used adaptively to modify behavior on a moment-to-moment basis and over longer time periods. During vocal behaviors, such as singing in songbirds, internal evaluation of motor performance relies on sensory input from the auditory and vocal-respiratory systems. Sensory input from the auditory system to the motor system, often referred to as auditory feedback, has been well studied in singing zebra finches (Taeniopygia guttata), but little is known about how and where nonauditory sensory feedback is evaluated. Here we show that brief perturbations in air sac pressure cause short-latency neural responses in the higher-order song control nucleus HVC (used as proper name), an area necessary for song learning and song production. Air sacs were briefly pressurized through a cannula in anesthetized or sedated adult male zebra finches, and neural responses were recorded in both nucleus parambigualis (PAm), a brainstem inspiratory center, and HVC, a cortical premotor nucleus. These findings show that song control nuclei in the avian song system are sensitive to perturbations directly targeted to vocal-respiratory, or viscerosensory, afferents and support a role for multimodal sensory feedback integration in modifying and controlling vocal control circuits. [ABSTRACT FROM AUTHOR]

Numerous factors influence the timing of spring migration in birds, yet the relative importance of intrinsic and extrinsic variables on migration initiation remains unclear. To test for interactions among weather, migration distance, parasitism, and physiology in determining spring departure date, we used the Dark‐eyed Junco (Junco hyemalis) as a model migratory species known to harbor diverse and common haemosporidian parasites. Prior to spring migration departure from their wintering grounds in Indiana, USA, we quantified the intrinsic variables of fat, body condition (i.e., mass ~ tarsus residuals), physiological stress (i.e., ratio of heterophils to lymphocytes), cellular immunity (i.e., leukocyte composition and total count), migration distance (i.e., distance to the breeding grounds) using stable isotopes of hydrogen from feathers, and haemosporidian parasite intensity. We then attached nanotags to determine the timing of spring migration departure date using the Motus Wildlife Tracking System. We used additive Cox proportional hazard mixed models to test how risk of spring migratory departure was predicted by the combined intrinsic measures, along with meteorological predictors on the evening of departure (i.e., average wind speed and direction, relative humidity, and temperature). Model comparisons found that the best predictor of spring departure date was average nightly wind direction and a principal component combining relative humidity and temperature. Juncos were more likely to depart for spring migration on nights with largely southwestern winds and on warmer and drier evenings (relative to cooler and more humid evenings). Our results indicate that weather conditions at take‐off are more critical to departure decisions than the measured physiological and parasitism variables. [ABSTRACT FROM AUTHOR]

Social wasps (Family: Vespidae) are opportunistic and generalist feeders, which can occasionally feed on live vertebrates. The German yellowjacket (Vespula germanica) is native to Eurasia and Northern Africa, and has invaded many countries around the world, producing several environmental, economic and social impacts. Here we report the first video‐recorded evidence that this wasp species preys on chicks. Over six breeding seasons, we studied the parental care behaviour of the Chilean Elaenia (Elaenia chilensis), a long‐distance migratory bird that breeds in the Andean‐Patagonian Forest. We filmed 59 nests when chicks were 2–3 and 10–11 days old, and recorded in a nest containing two 10‐day‐old nestlings the predation of one of them by German yellowjackets. The other chick was found alive on the ground, indicating that it escaped from the wasps. Parents did not defend offspring against wasp attacks. The rarity of this observation may suggest either that this insect is not yet a significant nest predator or that it is difficult to obtain a record of predation by wasps, because birds may remove dead nestlings from the nests (i.e. nest sanitation). Although Chilean Elaenia is not threatened, 41% of bird species in the Andean‐Patagonian Forest are endemic, and this new nest predator may potentially become a threat to the conservation of any of those species, which deserves further research. Hence, to evaluate the German yellowjacket impact on bird populations, it is imperative to conduct videotaped nest monitoring in order to remove the masking effect of nest sanitation on predator identity, which will allow to determine how much this wasp contributes to nest failure in the invaded zone of the Neotropical region. [ABSTRACT FROM AUTHOR]

Traffic noise is a pervasive pollutant that affects wildlife at individual and group levels through mechanisms such as disrupting communication, affecting antipredator strategy, and/or changing how they use space within a habitat. Urbanization is expanding rapidly—few places remain untouched by anthropogenic noise disturbance—so understanding the implications of noise on wildlife behavior is paramount to conservation efforts. We asked whether traffic noise could change space use and social network metrics in flocks of captive birds. Specifically, we quantified the effects of playbacks of traffic noise on individual sociality (weighted degree, number of social partners weighted by the frequency of interactions with those social partners) and flock clustering (global clustering coefficient, connectivity of neighbors). In this study, we recorded social interactions and space use of flocks of captive zebra finches (Taeniopygia guttata) before, during, and after an experimental traffic noise introduction in two treatments: high- and lower-amplitude noise. Our results demonstrated that individual sociality and flock clustering increased in response to the noise introduction in both high-amplitude and low-amplitude treatments. Additionally, birds in the high-amplitude treatment spent more time in the room with active playback during noise playback whereas birds in the lower-amplitude treatment decreased time spent in the room closest to the high-amplitude treatment. Increased social behavior in response to traffic noise could influence disease transmission, social learning, and mating dynamics. We suggest future studies explore the mechanisms driving increased social behavior in traffic noise, such as perceived predation risk, vigilance, and cross-sensory interference. [ABSTRACT FROM AUTHOR]

It is generally assumed that larger juveniles are more physiologically mature, hence their overall condition and subsequent performance are higher.Some taxa face extreme workload transitions during development (e.g. nest departure in birds), which may select for non‐linear growth profiles that decouple relationships between body size and physiological state, making the links between metrics of development (e.g. body mass) and juvenile performance uncertain.We manipulated perceived mass in European starlings approaching fledging using 4.0 g weighted backpacks, measuring subsequent growth trajectories (mass, wing length) and physiological state (aerobic capacity, energy state, oxidative status) to test whether body size and physiology are coupled during a non‐linear developmental phase (pre‐fledging mass recession). Nanotag radio transmitters were then used to track post‐fledging performance (activity, activity‐slope, dispersal).Weighted nestlings had greater pre‐fledging mass recession and marginally reduced wing growth when compared to controls. Consequently, weighted birds had lower body mass at fledging, while also displaying markers of oxidative stress (increased reactive oxygen metabolites), yet aerobic capacity and energy state were equal between treatment groups.Previously weighted birds showed no correlation between fledgling state (body size, physiology) and subsequent performance. However, control fledglings that had decreased mass recession and greater wing growth prior to fledging dispersed earlier, while longer wings at fledging were associated with more rapid increases in post‐fledging activity (activity‐slope). In addition, control fledglings with lower haemoglobin also dispersed earlier, while increased reactive oxygen metabolites were associated with decreased activity levels. Body mass and energy state were unrelated to any metric of post‐fledging performance.Our data suggest mass‐independent development of some physiological traits in species with non‐linear growth profiles, potentially with a context‐dependent oxidative cost, and that physiology may predict some measures of post‐fledging performance not captured by body size. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Despite avid interest in life history trade-offs and the costs of reproduction, evidence that increased parental allocation reduces subsequent breeding productivity is mixed. This uncertainty may be attributable to environmental heterogeneity in space and time, necessitating experiments across a range of ecological contexts. Over three breeding seasons, we cross-fostered clutches between nests to manipulate incubation duration in a wild population of Carolina wrens, a species in which only females incubate, to test for a cost of incubation on current and future reproduction. Prolonged incubation affected maternal productivity in a manner dependent on the current environment and initial investment in eggs, suggesting that incubation is optimized according to other components of reproduction and individual quality. Effects of incubation duration on foster nestling condition varied between years, being costly in one, beneficial in another, and neutral in the third. The proportion of young fledged, females' probability of breeding again within seasons, and subsequent clutch sizes all declined with increasing incubation effort—effects that became more pronounced as seasons progressed. Therefore, costs of incubation were almost entirely dependent on maternal quality and environmental variation, illustrating the importance of conducting experiments across a range of environmental settings for understanding the costs of reproduction and evolution of life histories. [ABSTRACT FROM AUTHOR]

Male Japanese bush warblers (Cettia diphone) produce not only typical songs but also long, conspicuous vocalizations (continuous songs) during the breeding season. In my preliminary observations, male warblers produced continuous songs in response to both the appearance of a predator and the calls of conspecific females. Although predator‐elicited vocalizations by males have been studied in some species, there are no known cases in which an acoustically identical vocalization is also triggered in response to conspecific females. Here, I examined whether these continuous songs triggered in response to predators and females were acoustically similar. In field experiments, I presented dummies of a Eurasian sparrowhawk and a female warbler before (April) and after (June) female arrival at the breeding ground. Before female arrival, 11.1% of males responded with continuous songs to each of the hawk and female presentations; after female arrival, the respective values were 27.6% and 48.3%. Thus, more males responded to the model presentations with continuous songs after female arrival. There was no difference in the acoustic characteristics of the continuous songs between the two models. The males approached the female model more intensively than the hawk model. These findings do not support the hypothesis that the song functions as an alarm or predator deterrent. The function of these continuous songs remains unclear, but this study is the first to show an example where males produce the same vocalization in response to both predators and conspecific females. The continuous song contains a trill‐like structure, which can be considered a performance‐related song trait. Therefore, the continuous song may possibly be an honest signal of male quality for females. Further studies are required to understand the function of this novel vocalization, particularly the effects of female breeding stage on male singing activity and the female response to the songs. [ABSTRACT FROM AUTHOR]

Here we investigate possible carryover effects of experimentally increased incubation temperatures for postnatal growth, metabolism, and parental care within and among 6 north temperate and one tropical songbird species. Increased temperatures during embryonic development consistently caused higher postnatal resting metabolism compared to control nests, among but not within the 7 species studied. The effects of the experiment on growth were species specific and depended on the morphometric considered. Size before the fledge date was positively correlated with feeding rate, and metabolism was lower in larger broods. Our experiment did not elicit changes in parental food delivery rates or brooding effort during the postnatal stage, and higher brooding effort was associated with nestlings of smaller mass and faster metabolism independently from treatment. Consequently, parental care seemed unlikely to be the cause of the differences in growth rates between treatments. Instead, physiological mechanisms triggered by our heating treatment appear to be responsible for the observed variation in growth. These intrinsic changes unmatched by adjustments in parental effort may contribute to longer-term consequences for individual quality and survival that deserve further attention. [ABSTRACT FROM AUTHOR]

Instances of parallel phenotypic evolution offer great opportunities to understand the evolutionary processes underlying phenotypic changes. However, confirming parallel phenotypic evolution and studying its causes requires a robust phylogenetic framework. One such example is the "black-and-white wagtails," a group of 5 species in the songbird genus Motacilla : 1 species, Motacilla alba , shows wide intra-specific plumage variation, while the 4r others form 2 pairs of very similar-looking species (M. aguimp  +  M. samveasnae and M. grandis  +  M. maderaspatensis , respectively). However, the 2 species in each of these pairs were not recovered as sisters in previous phylogenetic inferences. Their relationships varied depending on the markers used, suggesting that gene tree heterogeneity might have hampered accurate phylogenetic inference. Here, we use whole genome resequencing data to explore the phylogenetic relationships within this group, with a special emphasis on characterizing the extent of gene tree heterogeneity and its underlying causes. We first used multispecies coalescent methods to generate a "complete evidence" phylogenetic hypothesis based on genome-wide variants, while accounting for incomplete lineage sorting (ILS) and introgression. We then investigated the variation in phylogenetic signal across the genome to quantify the extent of discordance across genomic regions and test its underlying causes. We found that wagtail genomes are mosaics of regions supporting variable genealogies, because of ILS and inter-specific introgression. The most common topology across the genome, supporting M. alba and M. aguimp as sister species, appears to be influenced by ancient introgression. Additionally, we inferred another ancient introgression event, between M. alba and M. grandis. By combining results from multiple analyses, we propose a phylogenetic network for the black-and-white wagtails that confirms that similar phenotypes evolved in non-sister lineages, supporting parallel plumage evolution. Furthermore, the inferred reticulations do not connect species with similar plumage coloration, suggesting that introgression does not underlie parallel plumage evolution in this group. Our results demonstrate the importance of investing genome-wide patterns of gene tree heterogeneity to help understand the mechanisms underlying phenotypic evolution. [Gene tree heterogeneity; incomplete lineage sorting; introgression; parallel evolution; phylogenomics; plumage evolution; wagtails.] [ABSTRACT FROM AUTHOR]

Dispersal events offer a unique window into macroevolutionary processes, especially with respect to the effects of competition on diversification. Empirical studies testing alternative predictions of competitive effects are often limited in either geographic or phylogenetic scale. Here, we tested some of these hypotheses by comparing an assemblage of 16 oscine passerine clades, representing independent dispersal events into the Western Hemisphere, to their sister clades in the Eastern Hemisphere. We also compared the diversity of this assemblage of clades to an older, incumbent passerine clade in the Western Hemisphere, the suboscines. Specifically, we tested for ecological opportunity and incumbency-mediated constraints by analysis of clade-specific morphological disparities and rates of evolution relative to dispersal history. While there was no consistent outcome of oscine dispersal and macroevolution in the Western Hemisphere relative to their Eastern Hemisphere sister groups, most clades supported a role for ecological opportunity or incumbency effects, and such effects were better explained by differences in species accumulation than by differences in rates of trait evolution or colonization timing. This general pattern was not evident when comparing the entire oscine assemblage of the Western Hemisphere to the incumbent suboscine radiation; oscines and suboscines occupy comparable regions of functional trait diversity and, despite higher rates of trait evolution in oscines, these observations were consistent with simulated null expectations. This result suggests that oscine and suboscine assemblages may have evolved in relative isolation for a significant fraction of their history. [ABSTRACT FROM AUTHOR]

Combating the current biodiversity crisis requires the accurate documentation of population responses to human‐induced ecological change. However, our ability to pinpoint population responses to human activities is often limited to the analysis of populations studied well after the fact. Museum collections preserve a record of population responses to anthropogenic change that can provide critical baseline data on patterns of genetic diversity, connectivity, and population structure prior to the onset of human perturbation. Here, we leverage a spatially replicated time series of specimens to document population genomic responses to the destruction of nearly 90% of coastal habitats occupied by the Savannah sparrow (Passerculus sandwichensis) in California. We sequenced 219 sparrows collected from 1889 to 2017 across the state of California using an exome capture approach. Spatial–temporal analyses of genetic diversity found that the amount of habitat lost was not predictive of genetic diversity loss. Sparrow populations from southern California historically exhibited lower levels of genetic diversity and experienced the most significant temporal declines in genetic diversity. Despite experiencing the greatest levels of habitat loss, we found that genetic diversity in the San Francisco Bay area remained relatively high. This was potentially related to an observed increase in gene flow into the Bay Area from other populations. While gene flow may have minimized genetic diversity declines, we also found that immigration from inland freshwater‐adapted populations into tidal marsh populations led to the erosion of divergence at loci associated with tidal marsh adaptation. Shifting patterns of gene flow through time in response to habitat loss may thus contribute to negative fitness consequences and outbreeding depression. Together, our results underscore the importance of tracing the genomic trajectories of multiple populations over time to address issues of fundamental conservation concern. [ABSTRACT FROM AUTHOR]