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The pectoralis major is the muscle required for migratory flight in songbirds, and has been believed to be exclusively composed of fast oxidative glycolytic (FOG) fibers in most small songbirds (< 20 g). Here, we investigated the effect of season (migratory versus non-migratory) and migratory distance (within North America versus to South America) on muscle fiber type in three songbird families: vireos (Vireonidae), warblers (Parulidae), and thrushes (Turdidae). FOG and fast glycolytic (FG) fibers were identified using myosin-ATPase staining. Short-distance migrants within the vireo and warbler families altered their pectoralis muscle to contain FG fibers during non-migratory conditions, while long-distance migrants maintained exclusively FOG fibers, regardless of season. Thrushes, a family of larger songbirds, exhibited mixed fibers regardless of season or migratory distance. This study is one of the first to identify FG fibers in small North American songbirds and highlights the potential role of migratory distance and season on muscle phenotype. [ABSTRACT FROM AUTHOR]

Every year, several hundred million birds cross the Mediterranean on their migration from Eurasia to their wintering quarters in Africa. As many migrants travel at night or at high altitudes, direct observations of bird migration are difficult and thus our information about migrating species, numbers and timing is incomplete. An indirect way to assess autumn migration is the analysis of prey remains of Eleonora's Falcons (Falco eleonorae). These falcons breed in large colonies on islands in the Mediterranean and on the Canary Islands. Many migrants have to pass these islands on their flight to their African wintering quarters. Eleonora's Falcons appear to be adapted to the autumn bird migration and raise their young between August and October, when migrating birds are abundant. When nestlings have to be fed, falcons exclusively hunt small birds of 10 to 150 g body mass, whereas they prey mostly on aerial invertebrates (Coleoptera, Hymenoptera, Diptera, Orthoptera, Hemiptera, Odonata, Lepidoptera) from November to July. We studied Eleonora's Falcons from 1965 to 2001 on a rocky islet, north of Crete, which harboured a colony of about 200 breeding pairs. In 1969, 1971, 1977, and 1988 we systematically monitored and collected the pluckings and cached food items in 22 to 36 nest sites each year. Pluckings were systematically analysed later in Germany using a reference collection of bird feathers for identification. In total, we determined more than 111 prey species (mostly Passerines) comprising more than 13,450 individuals. The top 12 prey species were: Willow Warbler (27.8% of all prey items), Red-backed Shrike (10.7%), Spotted Flycatcher (9.9%), Whinchat (8.8%), Common Whitethroat (5.1%), Wood Warbler (3.8), Tree Pipit (2.9%), Icterine Warbler (2.5%), Greater Short-toed Lark (2.5%), Northern Wheatear (1.8%), Common Nightingale (1.6%), and European Pied Flycatcher (1.5%). Eleonora's Falcons are selective hunters to some degree; thus, the phenology and abundance data derived from the plucking analyses are biased towards slow-flying species or smaller birds (only up to a body mass of 150 g). When the young falcons develop and grow, food demand increases concomitantly. Comparing the total weight of prey over time indicates a correlation with food demand and in consequence with the number of prey items brought to the nest sites by the falcons. [ABSTRACT FROM AUTHOR]

Secondary cavity-nesting species must find natural cavities or artificial nest boxes to reproduce. Cavities are often limited, which results in intense interference competition among species that rely on them. Nest site shortages may exclude subordinate individuals from cavities and force them to adopt alternative reproductive tactics such as laying eggs in the nests of conspecifics or in the nests of other species. The Prothonotary Warbler (Protonotaria citrea) is a secondary cavity-nesting bird that opportunistically parasitizes conspecifics that has never been recorded parasitizing heterospecifics. Here, we report brood parasitism of a House Wren (Troglodytes aedon) nest by a Prothonotary Warbler and the subsequent fledging of a warbler from this nest. This is the first observation of interspecific brood parasitism for the Prothonotary Warbler and the first instance of interspecific brood parasitism by any New World warbler species. [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]

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]

Evolutionary radiations provide important insights into species diversification, which is especially true of adaptive radiations. New World wood warblers (Parulidae) are a family of small, insectivorous, forest-dwelling passerine birds, often considered an exemplar of adaptive radiation due to their rapid diversification followed by a slowdown. However, they deviate from the expectations of an adaptive radiation scenario due to the lack of conspicuous morphological and ecological differentiation. We fitted several macroevolutionary models to trait data in 105 species of wood warblers. We tested whether morphological traits underwent an early burst of evolution (suggesting adaptation to new ecological niches in adaptive radiations) and whether song and colour underwent a diversity-dependent acceleration of trait evolutionary rate (consistent with reproductive interference driving signal evolution). Morphology and song evolved gradually under stabilizing selection, suggesting niche conservatism, with morphology possibly acting as a constraint on song evolution. In contrast, many feather colour traits underwent a diversity-dependent burst of evolution occurring late in the clade's history. We suggest that a two-step process has led to the remarkable diversification of wood warblers. First, their early diversification probably proceeded by allopatric speciation. Second, feather colour divergence likely occurred during secondary contact after range expansion. This diversification of signalling traits might have facilitated species coexistence, in combination with behavioural niche partitioning. Wood warblers seem to present characteristics of both adaptive and non-adaptive radiations. [ABSTRACT FROM AUTHOR]

A study published in the Bulletin of the Ecological Society of America examines the relationship between the frequency of massive tree seed production (known as masting) in European deciduous forests and the population dynamics of wood warblers. The study finds that wood warblers reproduce less successfully in years following masts due to increased predator abundance, leading to lower population growth rates in regions with high mast frequency. The increasing frequency of mast years and average seed production, which are related to global warming, may also impact other species in resource-pulse driven ecosystems. The authors call for further demographic investigations of species affected by masting. [Extracted from the article]

Species abundance patterns are influenced by a myriad of factors, including habitat availability and ecological niche characteristics. However, the evidence concerning the specific impact factors such as niche position and niche breadth on mean and maximum abundances in vertebrates at a broad geographical scale remains inconclusive. In this study, we investigated the influence of niche position and breadth on the abundance of 47 species of birds belonging to the Parulidae family, commonly known as New World Warblers. We obtained data on abundance and presence records spanning the reproductive distribution of these species and employed the outlying mean index analysis to calculate niche position and niche breadth. We assessed the relationship between abundance metrics and niche descriptors using phylogenetic regressions to account for the non‐independence resulting from phylogenetic ancestry. Initially, we developed individual models for each predictor and subsequently formulated a multi‐predictor model encompassing niche position, niche breadth, and their interaction. Our findings revealed a negative relationship between niche position and both mean and maximum abundance, while niche breadth exhibited a positive relationship with these niche characteristics. Notably, the results of the multi‐predictor models indicated that niche position exerted the most substantial influence on both mean and maximum abundance. Additionally, the interaction between niche position and niche breadth had the most positive and significant contribution to mean population abundance. This study underscores the need for future research in other vertebrates to delve into the mechanisms underlying these patterns. Such endeavors will not only enhance our understanding of ecological dynamics but also equip us with predictive capabilities to anticipate population responses to environmental changes effectively. [ABSTRACT FROM AUTHOR]

This article explores the complexities and conflicting terminologies surrounding the study of avian moult. It discusses two main nomenclatures, the 'life-cycle' system and the Humphrey-Parkes or 'H-P' system, and argues for a standardized and globally applicable terminology based on scientific evidence. The text also delves into the different patterns of molting in bird species, such as preformative molt and simultaneous molt, and discusses the evolution of molting patterns in different bird groups. It concludes that molting patterns have evolved multiple times within the passerine group, with the simultaneous alternate molt being more common in migratory and resident species in harsh habitats. [Extracted from the article]

Migratory species inhabit many communities along their migratory routes. Across taxa, these species repeatedly move into and out of communities, interacting with each other and locally breeding species and competing for resources and niche space. However, their influence is rarely considered in analyses of ecological processes within the communities they temporarily occupy. Here, we explore the impact of migratory species on a breeding community using the framework of acoustic signal space, a limited resource in which sounds of species within communities co‐exist. Migrating New World warblers (Parulidae, hereafter referred to as migrant species) often sing during refueling stops in areas and at times during which locally breeding warbler species (hereafter breeding species) are singing to establish territories and attract mates. We used eBird data to determine the co‐occurrence of 19 migrant and 11 breeding warbler species across spring migration in SW Michigan, generated a signal space from song recordings of these species, and examined patterns of signaling overlap experienced by breeding species as migrants moved through the community. Migrant species were present for two‐thirds of the breeding season of local species, including periods when breeding species established territories and attracted mates. Signaling niche overlap experienced by individual breeding species was idiosyncratic and varied over time, yet niche overlap between migrant and breeding species occurred more commonly than between breeding species or between migrant species. Nevertheless, the proportion of niche overlap between migrant and breeding warblers was similar to overlap among breeding species. Our findings showed that singing by migrant species overlapped the signals of many breeding species, suggesting that migrants could have unexplored impacts on communication in breeding species, potentially affecting song detection and song evolution. Our study contributes to a growing body of research documenting the impacts of migratory species on communities and ecosystems. [ABSTRACT FROM AUTHOR]

Extra-pair paternity is widespread in passerine birds. The number of extra-pair young (EPY) varies among different species and populations of the same species. We tested if it is a case for a small passerine bird with poly-territorial behaviour, the Wood Warbler (Phylloscopus sibilatrix). The results are based on the microsatellite analysis of seven loci and revealed a high level of EPY in Central Russia population of Wood Warbler (EPY in 41% of all nests, 16 of 39 nests; 25% of all young were EPY, 52 of 212 young). We did not find relationship between relatedness among mates in the pair and the presence of EPY. There was no difference in heterozygosity and body mass between EPY and within pair young (WPY). Possible causes of extra-pair paternity are discussed. [ABSTRACT FROM AUTHOR]

The Pine Warbler (Setophaga pinus) inhabits eastern North America, where it breeds in the northern USA and Canada, and winters in southeastern USA. In Mexico, the species is considered an irregular winter migrant in the states of Nuevo Leon and Tamaulipas. We report the first record of the Pine Warbler for the state of Durango, in the protected area of the Cañon de Fernandez State Park, municipality of Lerdo. On 8 January 2023 at 11:42 h, a Pine Warbler was observed perched on a cypress tree (Taxodium huegelii), located on the banks of the Nazas River. The bird was on a branch approximately two meters above the ground. This record expands the species' winter distribution in Mexico. Observations like this are essential for confirming movements of species in time and space during migration, and for documenting changes in the distribution of migratory species. [ABSTRACT FROM AUTHOR]

Effective solutions to conserve biodiversity require accurate community‐ and species‐level information at relevant, actionable scales and across entire species' distributions. However, data and methodological constraints have limited our ability to provide such information in robust ways. Herein we employ a Deep‐Reasoning Network implementation of the Deep Multivariate Probit Model (DMVP‐DRNets), an end‐to‐end deep neural network framework, to exploit large observational and environmental data sets together and estimate landscape‐scale species diversity and composition at continental extents. We present results from a novel year‐round analysis of North American avifauna using data from over nine million eBird checklists and 72 environmental covariates. We highlight the utility of our information by identifying critical areas of high species diversity for a single group of conservation concern, the North American wood warblers, while capturing spatiotemporal variation in species' environmental associations and interspecific interactions. In so doing, we demonstrate the type of accurate, high‐resolution information on biodiversity that deep learning approaches such as DMVP‐DRNets can provide and that is needed to inform ecological research and conservation decision‐making at multiple scales. [ABSTRACT FROM AUTHOR]

The article discusses the use of the adjective "common" in bird species names. It explains that before standardized names, bird species had various regional or dialect names. In the 19th century, ornithologists and authors began using more appropriate non-scientific names, with "common" becoming a popular label. The article also mentions the adoption of new policies for bird names by national bird organizations, such as the British Ornithologists' Union. It concludes by providing examples of bird species with "common" in their names and discussing the appropriateness of the term in certain cases. [Extracted from the article]

Researchers often examine symbiont host specificity as a species‐level pattern, but it can also be key to understanding processes occurring at the population level, which are not as well understood. The specialist–generalist variation hypothesis (SGVH) attempts to explain how host specificity influences population‐level processes, stating that single‐host symbionts (specialists) exhibit stronger population genetic structure than multi‐host symbionts (generalists) because of fewer opportunities for dispersal and more restricted gene flow between populations. However, this hypothesis has not been tested in systems with highly mobile hosts, in which population connectivity may vary temporally and spatially. To address this gap, we tested the SGVH on proctophyllodid feather mites found on migratory warblers (family Parulidae) with contrasting host specificities, Amerodectes protonotaria (a host specialist of Protonotaria citrea) and A. ischyros (a host generalist of 17 parulid species). We used a pooled‐sequencing approach and a novel workflow to analyse genetic variants obtained from whole genome data. Both mite species exhibited fairly weak population structure overall, and contrary to predictions of the SGVH, the generalist was more strongly structured than the specialist. These results may suggest that specialists disperse more freely among conspecifics, whereas generalists sort according to geography. Furthermore, our results may reflect an unexpected period for mite transmission – during the nonbreeding season of migratory hosts – as mite population structure more closely reflects the distributions of hosts during the nonbreeding season. Our findings alter our current understanding of feather mite biology and highlight the potential for studies to explore factors driving symbiont diversification at multiple evolutionary scales. [ABSTRACT FROM AUTHOR]

On 29 October 2022, a first-year male Common Yellowthroat was found at Diga della Pèpa, Magadino (canton of Ticino). The bird was observed regularly until 13 December 2022, the date of its last observation in the area. This is the first record of this species in Switzerland, as well as the first Parulidae and only the second record of a North American songbird in Switzerland after a Song Sparrow Melospiza melodia was found in Turtmann-Unterems (canton of Valais) on 1 May 2010. This is a notable observation, since most North American passerines in Europe are recorded along the coast and on islands of the Atlantic and the North Sea. Of the 46 accepted records of Common Yellowthroats in Europe, this is the first in the inland of the continent. [ABSTRACT FROM AUTHOR]

Due to specific microclimatic conditions and accumulation of organic matter, bird nests are microhabitats that are often inhabited by various invertebrates, including mites (Acari). We tested whether nests of the ground-nesting passerine Phylloscopus sibilatrix (Bechstein) (Passeriformes: Phylloscopidae) [wood warbler] were associated with an increased local diversity of ptyctimous mites (Acari: Oribatida) on the forest floor in the Białowieża National Park, East Poland. In 2019–2020, we analysed 150 warbler nests shortly after they had been vacated by the birds, and additionally we sampled mites in leaf litter at 1 and 6 m distances from 21 of the collected nests. We found on average more mite species in nests sampled in 2020 than in nests sampled in 2019. Although the species composition largely overlapped between bird nests and the litter, bird nests contained a greater average number of mite species than litter samples, including species found only – Microtritia minima (Berlese) and Phthiracarus crenophilus Willmann – or mostly – Euphthiracarus cribrarius (Berlese) and Phthiracarus globosus (C.L. Koch) – in bird nests. The results suggest that the presence of bird nests may increase the local diversity of the invertebrate species assemblage. [ABSTRACT FROM AUTHOR]

This document is a report from the Inland Flyway Review - Spring 2023, which provides information on bird banding stations in the inland region of North America. The report includes data from 14 stations in Illinois, Ohio, Wisconsin, Michigan, Missouri, and Alabama. Most stations were able to operate normally after the Covid scenario, although some had health issues or low numbers. The report includes information on the number of birds banded, species captured, and highlights from each station. [Extracted from the article]

This article, published in the Florida Field Naturalist, explores the arthropods found on birds in Vaca Key, Monroe County, Florida. The author collected and identified different mites, such as Falculifer isodontus on Mourning Doves, Amerodectes hribari and Analges species on a Common Yellowthroat, Proctophyllodes breviquadratus and Ptilonyssus sairae on an Ovenbird, Analges allourus on a Common Myna, and Proctophyllodes hylocichlae on a thrush. The article provides valuable information about the arthropod fauna associated with these bird species in the area. It also mentions the discovery of an unidentified scatopsid, a type of black scavenger fly, on the plumage of a Common Yellowthroat. The presence of ectosymbiotic organisms on birds, including parasites and phoretic organisms, is still not well understood. The article acknowledges the contributions of various experts in identifying the organisms found and includes a list of references for further reading. [Extracted from the article]

A fundamental aspect of symbiotic relationships is host specificity, ranging from extreme specialists associated with only a single host species to generalists associated with many different species. Although symbionts with limited dispersal capabilities are expected to be host specialists, some are able to associate with multiple hosts. Understanding the micro- and macro-evolutionary causes of variations in host specificity is often hindered by sampling biases and the limited power of traditional evolutionary markers. Here, we studied feather mites to address the barriers associated with estimates of host specificity for dispersal-limited symbionts. We sampled feather mites (Proctophyllodidae) from a nearly comprehensive set of North American breeding warblers (Parulidae) to study mite phylogenetic relationships and host–symbiont codiversification. We used pooled-sequencing (Pool-Seq) and short-read Illumina technology to interpret results derived from a traditional barcoding gene (cytochrome c oxidase subunit 1) versus 11 protein-coding mitochondrial genes using concatenated and multispecies coalescent approaches. Despite the statistically significant congruence between mite and host phylogenies, mite–host specificity varies widely, and host switching is common regardless of the genetic marker resolution (i.e. barcode vs. multilocus). However, the multilocus approach was more effective than the single barcode in detecting the presence of a heterogeneous Pool-Seq sample. These results suggest that presumed symbiont dispersal capabilities are not always strong indicators of host specificity or of historical host–symbiont coevolutionary events. A comprehensive sampling at fine phylogenetic scales may help to better elucidate the microevolutionary filters that impact macroevolutionary processes regulating symbioses, particularly for dispersal-limited symbionts. [Codiversification; cophylogenetics; feather mites; host switching; pooled sequencing; species delineation; symbiosis, warblers.] [ABSTRACT FROM AUTHOR]

Animals that migrate in mixed-species groups may communicate with both conspecific and heterospecific individuals, providing a low-cost mechanism for navigation whenever individuals share similar migratory routes or destinations. Many migratory birds produce calls while flying, but the function of these calls, and the forces contributing to their evolution, are poorly known. We studied flight calls in mixed-species groups of wood warblers (Parulidae), a biodiverse group of migratory songbirds. We used a spatial approach to examine whether acoustic similarity of flight calls varies with group composition, recording flight calls of mixed-species flocks with a wireless microphone array and triangulating the positions of birds in three dimensions. We found that the acoustic similarity of flight calls was correlated with spatial proximity: birds with similar calls fly closer together during migration. We also found relationships between acoustic similarity, flock size and mixed-species flock diversity: birds with similar calls fly in smaller flocks and in flocks with lower species diversity. Our results support the idea that migrating birds use flight calls to maintain contact with acoustically similar individuals in mixed-species flocks, with communication transcending species boundaries. These results suggest that acoustically similar flight calls are used as cues of group assembly for migratory animals. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'. [ABSTRACT FROM AUTHOR]

Male songbirds undergo a suite of physiological changes during spring migration that prepare them to initiate breeding activities upon arrival at nesting sites. These physiological changes could result in the expression of sexual behaviors, such as singing, during the migratory period. Yet, mostly anecdotal observations of singing during stopovers exist in the literature. We explored singing by males of 20 species of New World warblers (Parulidae; hereinafter "warblers") during stopovers on spring migration through southwest Michigan. To explore patterns of stopover singing by males, we used eBird data to determine the migratory timing of each species in our region, superimposed singing observations on these migration schedules, and calculated song rates of migrating birds. We compared song rates of species during stopovers with those from breeding populations and examined whether interspecific variation in song rates depended on the distance to be traveled to the closest potential breeding range. We observed singing by males in 19 of 20 warbler species. Stopover singing differed from breeding season singing, as males sang at lower rates on stopovers than when they were in northern breeding areas. Species breeding farther from our study region showed larger intraspecific differences in song rates between stopover and breeding populations than those breeding in closer proximity. Moreover, interspecific variation in song rate was explained in part by the distance between our stopover area and the closest breeding area. Our results suggest that male warblers commonly sing during stopovers, at least at this latitude, and variation in singing across species could reflect physiological readiness to breed. Understanding the prevalence and rate of singing on spring migration stopovers highlights the behavioral outcomes of physiological changes occurring in male birds. Our study contributes new data on migratory singing to a body of research that has historically focused solely on birdsong within a breeding framework. Las aves canoras machos experimentan a una serie de cambios fisiológicos durante la migración primaveral que los preparan para iniciar actividades de reproducción al llegar a los sitios de reproducción. Estos cambios fisiológicos podrían dar lugar a la expresión de comportamientos sexuales, como el canto, durante el período migratorio. Sin embargo, la mayoría de las observaciones del canto durante las paradas migratorias que existen en la literatura son anecdóticas. Grabamos el canto de machos de 20 especies de reinitas del Nuevo Mundo (Parulidae; en adelante "reinitas") durante paradas en la migración primaveral a través del suroeste de Michigan. Para explorar los patrones de canto de los machos durante las paradas, usamos los datos de eBird para determinar el calendario migratorio de cada especie en nuestra región, superpusimos las observaciones de canto en estos horarios de migración y calculamos las tasas de canto de las reinitas migratorias. Comparamos las tasas de canto de las especies durante las paradas con las de las poblaciones reproductoras y examinamos si la variación interespecífica en las tasas de canto dependía de la distancia recorrida hasta el área potencial de reproducción más cercana. Observamos el canto de los machos en 19/20 especies de reinitas. El canto durante las paradas difería del canto de la temporada de reproducción, ya que los machos cantaban a tasas más bajas en las paradas que cuando estaban en las áreas de reproducción del norte. Las especies que se reproducen más lejos de nuestra región de estudio mostraron mayores diferencias intraespecíficas en las tasas de canto entre las poblaciones de parada y de reproducción que las que se reproducen más cerca. Además, la variación interespecífica en la tasa de canto se explicó en parte por la distancia entre nuestra área de parada y el área de reproducción más cercana. Nuestros resultados sugieren que las reinitas machos cantan comúnmente durante las paradas migratorias, al menos en esta latitud y la variación en el canto entre especies podría reflejar la preparación fisiológica para la reproducción. Comprender la prevalencia y la tasa de canto en las paradas migratorias de primavera destaca los resultados conductuales de los cambios fisiológicos que ocurren en las aves canoras macho. Nuestro estudio aporta nuevos datos sobre el canto migratorio a un cuerpo de investigación que históricamente se ha centrado únicamente en el canto de las aves canoras dentro de un contexto reproductivo. Palabras clave: canto de aves, canto de machos, canto durante la migración, canto durante la temporada no-reproductiva, comportamiento sexual, migración de primavera, sitios de parada migratoria. [ABSTRACT FROM AUTHOR]

Leucocytozoon parasites remain poorly investigated in comparison to other haemosporidians. The host cell inhabited by their blood stages (gametocytes) remains insufficiently known. This study aimed to determine the blood cells inhabited by Leucocytozoon gametocytes in different species of Passeriformes and to test if this feature has a phylogenetic importance. We microscopically analyzed blood films stained with Giemsa from six different bird species and individuals and used PCR-based methods for parasite lineage identification. The DNA sequences obtained were applied for phylogenetic analysis. Leucocytozoon parasite from the song thrush Turdus philomelos (cytochrome b lineage STUR1), the blackbird Turdus merula (undetermined lineage), the garden warbler Sylvia borin (unknown lineage) inhabited erythrocytes, a parasite from the blue tit Cyanistes caeruleus (PARUS4) infects lymphocytes, while in the wood warbler Phylloscopus sibilatrix (WW6) and the common chiffchaff Phylloscopus collybita (AFR205) they were found inhabiting thrombocytes. Parasites infecting thrombocytes were closely related, while the parasites infecting erythrocytes were placed in three different clades, and the one found in lymphocytes was placed in a separate clade. This shows that the determination of host cells inhabited by Leucocytozoon parasites can be phylogenetically important and should be considered in future species descriptions. Noteworthy, phylogenetic analysis might be used for the prediction of which host cells parasite lineages might inhabit. [ABSTRACT FROM AUTHOR]

Golden-winged Warblers (Vermivora chrysoptera, Parulidae) are declining migrant songbirds that breed in the Great Lakes and Appalachian regions of North America. Within their breeding range, Golden-winged Warblers are found in early successional habitats adjacent to mature hardwood forest, and previous work has found that Golden-winged Warbler habitat preferences are scale-dependent. Golden-winged Warbler Working Group management recommendations were written to apply to large regions of the breeding range, but there may be localized differences in both habitat availability and preferences. Rapid declines at the southernmost extent of their breeding range in Western North Carolina necessitate investigation into landscape characteristics governing distribution in this subregion. Furthermore, with the increase in availability of community science data from platforms such as eBird, it would be valuable to know if community science data produces similar distribution models as systemic sampling data. In this study, we described patterns of Golden-winged Warbler presence in Western North Carolina by examining habitat variables at multiple spatial scales using data from standardized Audubon North Carolina (NC) playback surveys and community science data from eBird. We compared model performance and predictions between Audubon NC and eBird models and found that Golden-winged Warbler presence is associated with sites which, at a local scale (150m), have less mature forest, more young forest, more herb/shrub cover, and more road cover, and at a landscape scale (2500m), have less herb/shrub cover. Golden-winged Warbler presence is also associated with higher elevations and smaller slopes. eBird and Audubon models had similar variable importance values, response curves, and overall performance. Based on variable importance values, elevation, mature forest at the local scale, and road cover at the local scale are the primary variables driving the difference between Golden-winged Warbler breeding sites and random background sites in Western North Carolina. Additionally, our results validate the use of eBird data, since they produce species distribution modeling results that are similar to results obtained from more standardized survey methods. [ABSTRACT FROM AUTHOR]

The wood warbler, Phylloscopus sibilatrix (Aves: Passeriformes), is a well-known model organism for studying bird migration, breeding habitat selection and nest predation. The nest acarofauna of this bird species has not been extensively studied so far. To provide a comprehensive report on mite species inhabiting wood warbler nests and to assess infestation parameters (prevalence, intensity, and abundance) for mite species and orders, we collected 45 nests of this bird species in the Wielkopolska National Park in western Poland. Analyses revealed a huge diversity (198 species) of mites inhabiting wood warbler nests. We found individuals belonging to the Mesostigmata, Trombidiformes and Sarcoptiformes. The Trombidiformes, represented in our study only by the Prostigmata, achieved statistically significantly lower intensity and abundance, compared to representatives of other orders. However, the number of recorded prostigmatid species was high (65). The most common were: Stigmaeus sphagneti (22 nests), Stigmaeus longipilis (16), Eupodes voxencollinus (15), Cunaxa setirostris (14), Stigmaeus pilatus (11), and Linopodes sp. 2 (10). The prevalence of Mesostigmata and Sarcoptiformes was equal, reaching 91.1%. Most of Gamasina (Mesostigmata) species found in this study were more characteristic of the soil environment and forest litter than bird nests, but there was also a typical bird parasite, viz. Ornithonyssus sylviarum. None of the observed species of Uropodina (Mesostigmata) or Oribatida (Sarcoptiformes) was typical for bird nests. Among the Uropodina, the highest parameters of nest infestation were achieved by Oodinychus ovalis, whereas among the Oribatida, they were achieved by Metabelba pulverosa. We discuss the importance of wood warbler nests for mite dispersal, survival and reproduction. [ABSTRACT FROM AUTHOR]

The timing of avian migration has evolved to exploit critical seasonal resources, yet plasticity within phenological responses may allow adjustments to interannual resource phenology. The diversity of migratory species and changes in underlying resources in response to climate change make it challenging to generalize these relationships.We use bird banding records during spring and fall migration from across North America to examine macroscale phenological responses to interannual fluctuations in temperature and long‐term annual trends in phenology.In total, we examine 19 species of North American wood warblers (family Parulidae), summarizing migration timing from 2,826,588 banded birds from 1961 to 2018 across 46 sites during spring and 124 sites during fall.During spring, warmer spring temperatures at banding locations translated to earlier median passage dates for 16 of 19 species, with an average 0.65‐day advancement in median passage for every 1°C increase in temperature, ranging from 0.25 to 1.26 days °C−1. During the fall, relationships were considerably weaker, with only 3 of 19 species showing a relationship with temperature. In those three cases, later departure dates were associated with warmer fall periods. Projecting these trends forward under climate scenarios of temperature change, we forecast continued spring advancements under shared socioeconomic pathways from 2041 to 2060 and 2081 to 2100 and more muted and variable shifts for fall.These results demonstrate the capacity of long‐distance migrants to respond to interannual fluctuations in temperatures, at least during the spring, and showcase the potential of North American bird banding data understanding phenological trends across a wide diversity of avian species. [ABSTRACT FROM AUTHOR]

Estimating fuel load and potential flight ranges of migrant passerines are basic issues in understanding bird migration strategies. Thirteen sub-Saharan and three pre-Saharan migrant passerine species were analysed in this study. The birds were captured at the Tömörd Bird Ringing Station in the western part of the Carpathian Basin. A general linear model with body mass as the dependent variable and fat score, muscle score and wing length as independent variables were used to estimate lean body mass (body mass without fuel deposits) and fuel load. In ten of the species studied, models considering interactions between factors fit the data better than the main-effect models. Body mass was positively correlated with the fat score in all species, with muscle score in ten species and wing length in 14 species. During autumn, fuel load tended to be larger in the sub-Saharan migrants, especially in four species which pass over the Mediterranean Sea, Common Nightingale (Luscinia megarhynchos), Icterine Warbler (Hippolais icterina), Garden Warbler (Sylvia borin) and Barred Warbler (Curruca nisoria). Nine sub-Saharan migrants, Marsh Warbler (Acro- cephalus palustris), Sedge Warbler (A. schoenobaenus), Eurasian Reed Warbler (A. scirpaceus), European Pied Flycatcher (Ficedula hypoleuca), Spotted Flycatcher (Muscicapa striata), Wood Warbler (Phylloscopus sibilatrix), Willow Warbler (Ph. trochilus), Common Whitethroat (C. communis) and Lesser Whitethroat (C. curruca) had estimated flight ranges similar (<1300 km) to two pre-Saharans, European Robin (Erithacus rubecula) and Eurasian Blackap (S. atricapilla). The three short-distance migrants, including the Common Chiffchaff (Ph. col- lybita) with the shortest distance, had sufficient fuel load to reach their southern European wintering sites without needing to refuel at stopover sites. [ABSTRACT FROM AUTHOR]

Conspecific attraction during habitat selection is common among animals, but the ultimate (i.e. fitness‐related) reasons for this behaviour often remain enigmatic.We aimed to evaluate the following three hypotheses for conspecific attraction during the breeding season in male Wood Warblers (Phylloscopus sibilatrix): the habitat detection hypothesis, the habitat choice copying hypothesis and the female preference hypothesis. These hypotheses make different predictions with respect to the relative importance of social and nonsocial information during habitat assessment, and whether benefits accrue as a consequence of aggregation.We tested the above hypotheses using a combination of a 2‐year playback experiment, spatial statistics and mate choice models.The habitat detection hypothesis was the most likely explanation for conspecific attraction and aggregation in male Wood Warblers, based on the following results: (1) males were attracted to conspecific song playbacks, but fine‐scale habitat heterogeneity was the better predictor of spatial patterns in the density of settling males; (2) male pairing success did not increase, but instead slightly decreased, as connectivity with other males (i.e. the number and proximity of neighbouring males) increased.Our study highlights how consideration of the process by which animals detect and assess habitat, together with the potential fitness consequences of resulting aggregations, are important for understanding conspecific attraction and spatially clustered distributions. [ABSTRACT FROM AUTHOR]

Copyright of Zeledonia is the property of Asociacion Ornitologica de Costa Rica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Anthropogenic climate change will dramatically alter species distributions. The rate and magnitude of range shifts, however, will differ among taxa, resulting in altered patterns of co-occurrence and interspecific interactions. We examined potential climate-mediated breeding range shifts among North American wood-warblers (Parulidae), a speciose avian family likely to be especially impacted by such changes due to high levels of interspecific competition and hybridization. We used publicly available species distribution model (SDM) range outputs to compare current ranges and patterns of sympatry among warbler species to future ranges and sympatry under 1.5°C, 2.0°C, and 3.0°C of average global warming. Range overlap among species and number of sympatric species are expected to decrease significantly in future warming scenarios, and unequal range shifts will alter the composition of warbler communities. On average, climate change will result in net decreases in the local species diversity; each warbler species is predicted to gain sympatry with approximately 1 new species and lose sympatry with approximately 2 species. Climate-mediated changes are predicted to differ among warblers in different regions of North America, with greatest impacts on eastern and boreal forest species. Our findings suggest that climate change will alter the diversity of wood-warbler communities during this century. Targeted monitoring of these changing interspecific relationships, especially for antagonistic interactions or hybridization between newly sympatric species, will be crucial for prioritizing particular species and regions in future conservation or management efforts. [ABSTRACT FROM AUTHOR]

Birds are among nature's most social animals. They are renowned for their group migrations, their cooperative foraging, their communal roosting, their synchronous breeding aggregations, their precise parent–offspring interactions, their coordinated group defenses and their intricate territorial and courtship rituals. In these and other contexts, and indeed in most moments of their lives, birds' capacities to navigate complex social demands and relationships can tip the balance between health or sickness, between reproductive success or failure, between life or death. It is thus no surprise that birds have evolved sophisticated systems for mediating social interactions. Foremost among these are communication signals, most evident in birds as songs, calls, color patterns and postural displays. These and other communication signals can transmit information about a signalers' status, motivations and possible future actions, for sensory and cognitive processing by signal receivers. In general, signals provide benefits for both signal senders and receivers. Consider the bright spring plumage of a male wood warbler who has established a breeding territory. The male's plumage pattern benefits him by signaling his 'ownership' of his territory, which can help him attract potential mates and preempt conflict with potential rivals. His plumage pattern also benefits his intended audiences: it informs females about the signaler's potential as a mate, and it informs other males about the degree of threat they might face were they to attempt a territory take-over. Communication signals are, in essence, a glue that maintains the cohesion of bird societies, and a currency that mediates sophisticated relationships within. Jeff Podos and Mike Webster introduce the structure, ecology and evolution of bird acoustic signals. [ABSTRACT FROM AUTHOR]

We used whole-genome resequencing to estimate genetic distinctiveness in the Black-throated Green Warbler (Setophaga virens)--including S. v. waynei--a putative subspecies that occupies a narrow disjunct breeding range along the Atlantic Coastal Plain. Despite detecting low-global differentiation (FST = 0.027) across the entire species, the principal components analysis of genome-wide differences shows the main axis of variation separates S. v. waynei from all other S. v. virens samples. We also estimated a low-migration rate for S. v. waynei, but found them to be most similar to another disjunct population from the Piedmont of North Carolina, and detected evidence of a historical north-to-south geographic dispersal among the entire species. New World wood warblers (family: Parulidae) can exhibit strong phenotypic differences among species, particularly, in song and plumage; however, within-species variation in these warblers--often designated as subspecies--is much more subtle. The existence of several isolated Black-throated Green Warbler populations across its eastern North American breeding range offers an excellent opportunity to further understand the origin, maintenance, and conservation status of subspecific populations. Our results, combined with previously documented ecological and morphological distinctiveness, support that S. v. waynei be considered a distinct and recognized subspecies worthy of targeted conservation efforts. [ABSTRACT FROM AUTHOR]

During migration, birds must stopover at refueling sites to replenish energy stores, with the rate of refueling linked to stopover length, migration speed, and the timing of critical life stages, such as breeding. Under optimal migration theory, birds are expected to maximize fuel intake and minimize stopover length (the time minimization hypothesis). Within a multi-species framework, we demonstrate that time minimization behavior is context-dependent, as refueling rate, stopover length, and departure decisions vary between seasons, among species with different ecological traits (e.g., diet and migration distance), and in response to density-dependent factors and prevailing environmental conditions. Using long-term banding data (10 years) from southwestern British Columbia, Canada, we investigated the ecological processes shaping stopover dynamics among 5 warbler (Parulidae) and 5 sparrow species (Passerellidae). Specifically, we assessed variation in fuel deposition rates (FDRs) as well as the associations between mass gain, stopover length, and departure probability. FDR was greater in insectivorous warblers during spring migration and in species migrating long distances. FDR responded positively to temperature and habitat productivity, but negatively to precipitation events, particularly for insectivorous, long-distance migrants during spring migration. Similarly, density-dependent refueling rate was only observed in insectivores and long-distance migrants during spring migration, where higher densities of foliage-gleaning insectivores were associated with a lower FDR. Stopover duration was more closely associated with body condition upon arrival and subsequent mass gain than direct environmental effects, especially during northward spring migration, providing support for time minimization and a mass threshold influencing departure decisions. These results highlight that refueling rates and stopover quality vary among species depending on their life-history strategies, with particular implications for long-distance, migratory insectivores, which may be most susceptible to climate shifts. [ABSTRACT FROM AUTHOR]

Nest predation is the primary cause of nest failure in most ground‐nesting bird species. Investigations of relationships between nest predation rate and habitat usually pool different predator species. However, such relationships likely depend on the specific predator involved, partly because habitat requirements vary among predator species. Pooling may therefore impair our ability to identify conservation‐relevant relationships between nest predation rate and habitat. We investigated predator‐specific nest predation rates in the forest‐dependent, ground‐nesting wood warbler Phylloscopus sibilatrix in relation to forest area and forest edge complexity at two spatial scales and to the composition of the adjacent habitat matrix. We used camera traps at 559 nests to identify nest predators in five study regions across Europe. When analyzing predation data pooled across predator species, nest predation rate was positively related to forest area at the local scale (1000 m around nest), and higher where proportion of grassland in the adjacent habitat matrix was high but arable land low. Analyses by each predator species revealed variable relationships between nest predation rates and habitat. At the local scale, nest predation by most predators was higher where forest area was large. At the landscape scale (10,000 m around nest), nest predation by buzzards Buteo buteo was high where forest area was small. Predation by pine martens Martes martes was high where edge complexity at the landscape scale was high. Predation by badgers Meles meles was high where the matrix had much grassland but little arable land. Our results suggest that relationships between nest predation rates and habitat can depend on the predator species involved and may differ from analyses disregarding predator identity. Predator‐specific nest predation rates, and their relationships to habitat at different spatial scales, should be considered when assessing the impact of habitat change on avian nesting success. [ABSTRACT FROM AUTHOR]

Differences in population trends across a species' breeding range are ultimately linked to variation in demographic rates. In small songbirds, demographic rates related to fecundity typically have strong effects on population trends. Populations of a forest songbird, the wood warbler Phylloscopus sibilatrix, have been declining in many but not all regions of the European breeding range. We investigated if clutch size, hatching rate, nest survival and number of fledglings vary across Europe, and if nest survival is related to differences in the regionally dominant nest predator class (birds versus mammals). From 2009 to 2020, we monitored 1896 nests and used cameras at a subsample of 645 nests in six study regions: the United Kingdom (mid‐Wales, Dartmoor, the New Forest), Germany (Hessen), Switzerland (Jura mountains) and Poland (Białowieża National Park). Number of fledglings was lowest in the New Forest (1.43 ± CI 0.23), intermediate in Jura (2.41 ± 0.31) and Białowieża (2.26 ± 0.24) and highest in mid‐Wales (3.02 ± 0.48) and Dartmoor (2.92 ± 0.32). The reason for low reproductive success in the New Forest, Jura and Białowieża was low nest survival, and large clutch sizes in Białowieża did not compensate for high nest losses. High reproductive success in mid‐Wales and Dartmoor was due to high nest survival and large clutch sizes. Overall predation rates were similar everywhere despite variation between the regions in the dominant nest predator class. Unsuccessful nests in mid‐Wales were mainly predated by birds; in Dartmoor, the New Forest, Hessen and Jura similarly by birds and mammals; and in Białowieża exclusively by mammals. Regional reproductive success does not match the population trends recently reported for the wood warbler in the six study regions (i.e. high reproduction ≠ positive trend). Annual survival may be a decisive factor, but it is difficult to quantify for a nomadic species such as the wood warbler that rarely returns to the same breeding locations. [ABSTRACT FROM AUTHOR]

Animal communication, including the transmission of risk-related information, has long been recognized as occurring in a network, rather than being limited to signaller–receiver dyadic interactions. However, it is rare for studies on communication to explicitly incorporate a network approach and for network studies to focus on communication interactions and information transmission in nongrouping species. Consequently, the properties of communication networks and the extent to which risk-related information can spread through populations of territorial animals remain largely unexplored. Here, I examined the structure and spatial extent of eavesdropping networks by studying alarm calls in wood warblers, Phylloscopus sibilatrix, small, territorial songbirds inhabiting temperate European forests. Using a playback experiment, I first established the active space of wood warblers' alarm signals, that is, how the strength of antipredator responses to conspecific alarm calls varies as a function of distance between signallers and receivers. Next, I combined social network analysis and fine-scale, long-term data on wood warblers' territory distribution to delineate spatially explicit alarm call eavesdropping networks and to explore the potential for risk-related information transmission at the population level. Response strength of wood warblers to conspecific calls decreased with increasing distance to callers, suggesting distance-dependent eavesdropping. However, each year the majority of individuals occupied territories within the active space of alarm signals of multiple neighbours and could reach information from even more of them via indirect links. Moreover, the patterns of connections between individuals were generally similar across years, suggesting that basic network properties remain stable over time. This study shows that during the spring breeding season, individual birds are interlinked with conspecifics across territory borders into population-wide information webs, in which risk-related information can readily spread across large spatial scales. In turn, this highlights the social environment as an important dimension of individuals' niches even in otherwise territorial animals. • I examined the structure and extent of eavesdropping networks in wood warblers. • Eavesdropping on conspecific alarm calls was distance dependent. • Birds held territories within the active space of alarm signals of many neighbours. • Basic properties of alarm call eavesdropping networks remained stable over time. • Territorial birds during the breeding season form population-wide information webs. [ABSTRACT FROM AUTHOR]

Temperature plays an important role in determining the breeding phenology of birds in temperate climates, with higher spring temperatures associated with earlier breeding. However, the effect of localised territory‐scale temperature variations is poorly understood, with relationships between temperature and breeding phenology mostly studied using coarse‐grained climatic indices. Here, we interpolate spring temperatures recorded at 150‐m2 grid intersections encompassing 417 ha of forest to examine the influence of territory‐scale temperature, and its interaction with mean annual temperature, on territory selection, breeding phenology, clutch size and fledging success for three co‐occurring single‐brooded passerine birds using data from 672 nests over four years. All species exhibited significant trends in reproductive traits associated with territory‐scale temperature. Pied flycatchers Ficedula hypoleuca settled in cooler territories first, where they raised more fledglings. Blue tits Cyanistes caeruleus laid larger clutches in warmer territories in warm years and always laid earlier at warmer territories irrespective of annual temperature variation. Contrastingly, pied flycatcher and wood warbler Phylloscopus sibilatrix breeding phenology was earlier at warmer territories in cool years and cooler territories in warm years, with wood warbler clutch size responding similarly to this interaction. Greater previous breeding experience and higher rates of historical territory occupancy (territory quality) also predicted earlier breeding phenology and higher fledging success for pied flycatchers. We suggest that the migratory pied flycatcher and wood warbler are best synchronised with their prey availability in cooler years at a local population level. However resident blue tits match local phenology across all years, which is potentially advantageous under warmer predicted climate change scenarios. We conclude that temperature at the territory scale can be an important driver of settlement and breeding phenology and influence reproductive traits. [ABSTRACT FROM AUTHOR]

The article provides a detailed account of the breeding biology of the Bornean Stubtail (Urosphena whiteheadi), focusing on its reproductive traits and comparing them with other members of its family. Topics include the bird's breeding strategies and life-history traits, its nesting behavior and incubation period, and the differences observed in comparison to other Cettiidae warblers.

The extent to which interspecific competition structures species interactions and coexistence within communities, and the relevant mechanisms, are still debated. We focus on New World wood warblers (Parulidae), beginning with Robert MacArthur's iconic 1958 paper in which he shows how subtle foraging behaviors, purportedly linked to dietary differences, within spruce trees contribute to the coexistence of 5 spruce-woods warbler species. MacArthur coined the phrase "resource partitioning", and profoundly impacted the field of Ecology for subsequent decades in diverse ways. To understand what MacArthur got right and what he missed, we reviewed both ecological and evolutionary approaches to questions of the origin and coexistence of competing species in the context of diet. We argue that an important, underappreciated, mechanism of competition among coexisting migratory warbler species, particularly in winter, is diffuse exploitation competition, based in part on our own studies of warbler diets in relation to foraging behavior, substrate use, bird morphology, and other traits. Our review and synthesis of interspecific competition and coexistence in warblers have important consequences, including our questioning of the importance and effectiveness of resource partitioning in birds. We also suggest a novel hypothesis for the success of warblers today in the Caribbean and other habitats, beginning with their relatively recent adaptive radiation and the ecological opportunity on Caribbean islands. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Field Ornithology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The city of Caracas has a large number of bird species, however, scientific publications regarding the migratory species that visit it is very poor. The objective of this study consisted of making a compilation of the migratory species reported for the city. For the elaboration of this study, bibliographic sources available in scientific journals, bird guides and the eBird page were consulted. As a result, 51 northern migratory species were identified, two austral migratory, and 12 species with resident and migratory populations. The most diverse family was Parulidae with 17 species, followed by Scolopacidae, with 10 species, and Hirundinidae, with four. All migratory from the north. The species with the highest number of sightings were the parulidae Northern Waterthrush (Parkesia noveboracensis) (n = 91), American Redstart (Setophaga ruticilla) (n = 82) and Yellow Warbler (Setophaga petechia) (n = 42). Among the most important sightings is the Green Heron (Butorides virescens), a rare species, with few observations for the country. Other rare species, with only one or two reports for Caracas, were Louisiana Waterthrush (Parkesia motacilla), Baltimore Oriole (Icterus galbula) and Bobolink (Dolichonyx oryzivora), and species considered probable as Cape May Warbler (Dendroica tigrina), of which there is no record yet. These results show the importance of databases such as eBird and the Citizen Science for the knowledge of the world's avifauna. [ABSTRACT FROM AUTHOR]

Although both interspecific competition and coexistence mechanisms are central to ecological and evolutionary theory, past empirical studies have generally focused on simple (two‐species) communities over short time periods. Experimental tests of these species interactions are challenging in complex study systems. Moreover, several studies of 'imperfect generalists', consistent with Liem's Paradox, raise questions about the ability of evolved species differences to partition niche space effectively when resources vary considerably across the annual cycle. Here we used a recently developed theoretical framework to combine past research on population‐level processes with observational data on resource use to test for ongoing interspecific competition and understand the nature of resource overlap. We compared species diet overlaps and differences in several distinctive communities centred on a focal species, the American Redstart Setophaga ruticilla replicated both spatially and seasonally, in combination with documentation of population regulation to assess the ability of similar species to partition dietary niche space and limit interspecific competition. Our results document high dietary overlap in most of the communities studied, with only subtle differentiation consistent with known species differences in foraging behaviour and morphology. These findings are largely consistent with species foraging as imperfect generalists. However, in contrast to past studies, the high diet overlaps observed here during times of inferred resource scarcity were driven by low‐value prey taxa (e.g. small ants) and did not involve truly 'private' resources. All of these factors increase the potential negative impacts of interspecific competition, and limit the ability of these birds to avoid competition if food availability deteriorates further than observed in our study, either seasonally or at longer intervals. [ABSTRACT FROM AUTHOR]

The Cerulean Warbler (Setophaga cerulea), a Neotropical migrant passerine, inhabits deciduous forests across the eastern and midwestern United States and Canada. Within this broad geographic distribution, Cerulean Warbler populations select specific tree species for nest placement and are known to use a variety of deciduous tree species depending on the population. In southern Indiana, Cerulean Warblers typically nest in white oak (Quercus alba), but we have documented 19 tree species used, all of which are deciduous species. During 2018 and 2019, we discovered 2 instances of Cerulean Warblers nesting in pine trees (Pinaceae) in southern Indiana. Our observations suggest that Cerulean Warblers may in some instances select atypical nest sites as long as specific microhabitat characteristics are present at the nest location. [ABSTRACT FROM AUTHOR]