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Hybridization and resulting introgression can play both a destructive and a creative role in the evolution of diversity. Thus, characterizing when and where introgression is most likely to occur can help us understand the causes of diversification dynamics. Here, we examine the prevalence of and variation in introgression using phylogenomic data from a large (1300+ species), geographically widespread avian group, the suboscine birds. We first examine patterns of gene tree discordance across the geographic distribution of the entire clade. We then evaluate the signal of introgression in a subset of 206 species triads using Patterson's D-statistic and test for associations between introgression signal and evolutionary, geographic, and environmental variables. We find that gene tree discordance varies across lineages and geographic regions. The signal of introgression is highest in cases where species occur in close geographic proximity and in regions with more dynamic climates since the Pleistocene. Our results highlight the potential of phylogenomic datasets for examining broad patterns of hybridization and suggest that the degree of introgression between diverging lineages might be predictable based on the setting in which they occur.

Social selection, via intra- and intersexual competition for sexual (e.g. mates) and/or nonsexual (e.g. territories) resources, is thought to drive the evolution of ornaments in both sexes. However, the relative importance of intra- and intersexual competition in promoting the evolution of female and male ornamentation and, hence, sexual dichromatism remains poorly understood. We addressed this issue in antbirds (Thamnophilidae), a radiation of sexually dichromatic passerines wherein eumelanic plumage patches have evolved multiple times in both sexes. In antbirds, the degree of sexual dichromatism differs between closely related species primarily due to eumelanic dark patches in either sex. If eumelanic patches evolved by social selection, individuals of species bearing more conspicuous eumelanic patches should display stronger territorial responses regardless of their sex. Using playback experiments, we simulated three conspecific territorial intrusion types – a social pair, a female and a male – and measured responses by social pairs of two sister species pairs exhibiting greater interspecific differences in female coloration and one sister species pair exhibiting greater interspecific differences in male coloration. We found that females of species bearing more conspicuous eumelanic patches responded more strongly than females of species bearing less conspicuous eumelanic patches, but only towards simulated female and/or male intruders. However, males responded similarly to all intrusions regardless of interspecific coloration differences. Our results suggest that eumelanic patches in antbirds may function as ornaments and that greater female ornamentation may function in intra- and intersexual contexts and reflect stronger social competition in ornamented females for territories and, possibly, mates. In contrast, in species pairs with greater interspecific differences in male ornamentation, territorial competition may occur predominantly among males and female mate choice may drive the evolution of male ornamentation. Our study highlights that social selection pressures acting on both sexes may drive the evolution of contrasting sexual dichromatism patterns.

Noise pollution is an unprecedented evolutionary pressure on wild animals that can lead to alteration of stress hormone levels and changes in foraging behavior. Both corticosterone and feeding behavior can have direct effects on gut bacteria, as well as indirect effects through changes in gut physiology. Therefore, we hypothesized that exposure to noise will alter gut microbial communities via indirect effects on glucocorticoids and foraging behaviors. We exposed captive white-crowned sparrows to city-like noise and measured each individuals' corticosterone level, food intake, and gut microbial diversity at the end of four treatments (acclimation, noise, recovery, and control) using a balanced repeated measures design. We found evidence that noise acts to increase corticosterone and decrease food intake, adding to a growing body of research indicating noise exposure affects stress hormone levels and foraging behaviors. We also found evidence to support our prediction for a causal, positive relationship between noise exposure and gut microbial diversity, such that birds had higher measures of alpha diversity during noise exposure. These results help to explain previous findings that urban, free-living white-crowned sparrows have higher bacterial richness than rural sparrows. However, noise appeared to act directly on the gut microbiome or, more likely, through an unmeasured variable, rather than through indirect effects via corticosterone and food intake. Altogether, our study indicates that noise affects plasma corticosterone, feeding behavior, and the gut microbiome in a songbird and raises new questions as to the mechanism linking noise exposure to gut microbial diversity.

Global climate change is causing heatwaves to increase in number, length and intensity. These extreme temperatures can reduce fitness when mating behaviours are affected. An important mating behaviour for many organisms is sexual signalling. For example, songbirds, such as the zebra finch, Taeniopyggia guttata, use song to attract mates. Here, we test how an acute period of extreme heat affects song production in male zebra finches. We then ask whether female zebra finches discriminate between songs produced at different temperatures. We find that males significantly reduce song output at temperatures that induce heat dissipation behaviours. We also find that males produce song bouts with shorter syllables when thermally challenged. Furthermore, the relative acoustic and structural consistency of songs changes with temperature. Finally, we find that female zebra finches discriminate between songs produced at different temperatures, and the strength of discrimination is associated with changes in syllable duration. Altogether, we demonstrate that heatwave-like conditions can impact communication via alterations in signaller behaviour and the signal itself. We also discuss the potential compounding effects of reduced song production and other physiological declines on fitness in free-living zebra finches, which increasingly experience these high temperatures.

Selection on signals that mediate social competition varies with resource availability. Climate regulates resource availability, which may affect the strength of competition and selection on signals. Traditionally, this meant that more seasonal, colder, or dryer-overall harsher-environments should favor the elaboration of male signals under stronger male-male competition, increasing sexual dimorphism. However, females also use signals to compete; thus, harsher environments could strengthen competition and favor elaboration of signals in both sexes, decreasing sexual dimorphism. Alternatively, harsher environments could decrease sexual dimorphism due to scarcer resources to invest in signal elaboration in both sexes. We evaluated these contrasting hypotheses in antbirds, a family of Neotropical passerines that varies in female and male signals and occurs across diverse climatic regimes. We tested the association of sexual dimorphism of plumage coloration and songs with temperature, precipitation, and their seasonality. We found that greater seasonality is associated with lower sexual dimorphism in plumage coloration and greater elaboration of visual signals in both sexes, but not acoustic signals. Our results suggest that greater seasonality may be associated with convergent elaboration of female and male visual signals, highlighting the role of signals of both sexes in the evolution of sexual dimorphism.

Songbirds reclaim favored frequencies When severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic lockdowns were instituted across entire countries, human activities ceased in an unprecedented way. Derryberry et al. found that the reduction in traffic sound in the San Francisco Bay Area of California to levels not seen for half a century led to a shift in song frequency in white-crowned sparrows (see the Perspective by Halfwerk). This shift was especially notable because the frequency of human-produced traffic noise occurs within a range that interferes with the highest performance and most effective song. Thus, our “quiet” allowed the birds to quickly fill the most effective song space. Science , this issue p. 575 ; see also p. 523

Correlative evidence suggests that high problem‐solving and foraging abilities in a mate are associated with direct fitness advantages, so it would benefit females to prefer problem‐solving males. Recent work has also shown that females of several bird species who directly observe males prefer those that can solve a novel foraging task over those that cannot. In addition to or instead of direct observation of cognitive skills, many species utilize assessment signals when choosing a mate. Here, we test whether females can select a problem‐solving male over a non‐solving male when presented only with a signal known to be used in mate assessment: song. Using an operant conditioning assay, we compared female zebra finch (Taeniopygia guttata) preference for the songs of males that could quickly solve a novel foraging task to the songs of males that could not solve the task. Females were never housed with the test subject males whose song they heard, and the only information provided about the males was their song. We found that females elicited more songs of problem‐solving males than of non‐solvers, indicating that song may contain information about a male’s ability to solve a novel foraging task and that naïve females prefer the songs of problem‐solving males., Birdsong is known to be an indicator of overall brain function and developmental conditions, but it is unknown whether song can reflect cognitive or personality traits that specifically affect foraging tasks. Here, we tested female preference for song from males who could quickly solve or could not solve an artificial novel foraging task. Although females had no prior knowledge of males, they solicited more song from males who could quickly solve the novel foraging task.

Habitats are changing rapidly around the globe and urbanization is one of the primary drivers. Urbanization changes food availability, environmental stressors, and the prevalence of disease for many species. These changes can lead to divergence in phenotypic traits, including behavioral, physiological, and morphological features between urban and rural populations. Recent research highlights that urbanization is also changing the gut microbial communities found in a diverse group of host species. These changes have not been uniform, leaving uncertainty as to how urban habitats are shaping gut microbial communities. To better understand these effects, we investigated the gut bacterial communities of White-Crowned Sparrow (Zonotrichia leucophrys) populations along an urbanization gradient in the San Francisco Bay area. We examined how gut bacterial communities vary with the local environment and host morphological characteristics. We found direct effects of environmental factors, including urban noise levels and territory land cover, as well as indirect effects through body size and condition, on alpha and beta diversity of gut microbial communities. We also found that urban and rural birds’ microbiomes differed in which variables predicted their diversity, with urban communities driven by host morphology, and rural communities driven by environmental factors. Elucidating these effects provides a better understanding of how urbanization affects wild avian physiology.

As urbanization expands globally, the communication systems of an increasing number of species are affected. Because bird song is a long-distance signal used to attract mates and defend territories, the evolution of bird song is often shaped by habitat structure and background noise. These potential drivers of song evolution are more often studied in natural areas than in urbanized areas, leaving open the question of how anthropogenic changes to the landscape are affecting the evolution of bird song. One songbird that persists in both urbanized and rural areas in North America is the White-crowned Sparrow (Zonotrichia leucophrys). Our previous work demonstrates that increased background noise in cities and in natural habitats affects acoustic adaptation in this species. However, we lack information about how sound transmits in urban and rural habitats. Because cities tend to have different physical properties than rural areas, it is pertinent to understand the influence of urban habitat structure on song evolutionary processes. Here, we test the acoustic adaptation theory and hypothesize that differences in the sound transmission properties of urban and rural habitats affect song divergence between urban and rural populations. We conducted sound transmission trials of tones from 1 to 8 kHz on 59 White-crowned Sparrow territories in three urban and three rural locations around San Francisco and Point Reyes, California, at varying heights and rates of note production. We also recorded and analyzed songs of males from each location to see if differences in signal–noise ratio, attenuation, reverberation, and distortion predicted song divergence. We found that urban locations have higher attenuation and reverberation than rural locations and urban songs tend to have short whistles, faster trills, and narrower bandwidth. These findings partially support acoustic adaptation theory, though faster trills in the city may instead be driven by cultural drift or sexual selection. Overall, our results add to a rapidly growing area of research and allow us to better understand the complexity of influences on song divergence.

In a rapidly warming world, exposure to high temperatures may impact fitness, but the gene regulatory mechanisms that link sublethal heat to sexually selected traits are not well understood, particularly in endothermic animals. Our experiment used zebra finches (Taeniopygia guttata), songbirds that experience extreme temperature fluctuations in their native Australia. We exposed captive males to an acute thermal challenge (43°C) compared with thermoneutral (35°C) and lower (27°C) temperatures. We found significantly more heat dissipation behaviours at 43°C, a temperature previously shown to reduce song production and fertility, and more heat retention behaviours at 27°C. Next, we characterized transcriptomic responses in tissues important for mating effort-the posterior telencephalon, for its role in song production, and the testis, for its role in fertility and hormone production. Differential expression of hundreds of genes in the testes, but few in the brain, suggests the brain is less responsive to extreme temperatures. Nevertheless, gene network analyses revealed that expression related to dopaminergic signalling in the brain covaried with heat dissipation behaviours, providing a mechanism by which temporary thermal challenges may alter motivational circuits for song production. In both brain and testis, we observed correlations between thermally sensitive gene networks and individual differences in thermoregulatory behaviour. Although we cannot directly relate these gene regulatory changes to mating success, our results suggest that individual variation in response to thermal challenges could impact sexually selected traits in a warming world.

Tobias, Joseph A., Sheard, Catherine, Pigot, Alex L., Devenish, Adam J. M., Yang, Jingyi, Sayol, Ferran, Neate‐Clegg, Montague H. C., Alioravainen, Nico, Weeks, Thomas L., Barber, Robert A., Walkden, Patrick A., MacGregor, Hannah E. A., Jones, Samuel E. I., Vincent, Claire, Phillips, Anna G., Marples, Nicola M., Montaño‐Centellas, Flavia A., Leandro‐Silva, Victor, Claramunt, Santiago, Darski, Bianca, Freeman, Benjamin G., Bregman, Tom P., Cooney, Christopher R., Hughes, Emma C., Capp, Elliot J. R., Varley, Zoë K., Friedman, Nicholas R., Korntheuer, Heiko, Corrales‐Vargas, Andrea, Trisos, Christopher H., Weeks, Brian C., Hanz, Dagmar M., Töpfer, Till, Bravo, Gustavo A., Remeš, Vladimír, Nowak, Larissa, Carneiro, Lincoln S., Moncada R., Amilkar J., Matysioková, Beata, Baldassarre, Daniel T., Martínez‐Salinas, Alejandra, Wolfe, Jared D., Chapman, Philip M., Daly, Benjamin G., Sorensen, Marjorie C., Neu, Alexander, Ford, Michael A., Mayhew, Rebekah J., Fabio Silveira, Luis, Kelly, David J., Annorbah, Nathaniel N. D., Pollock, Henry S., Grabowska‐Zhang, Ada M., McEntee, Jay P., Carlos T. Gonzalez, Juan, Meneses, Camila G., Muñoz, Marcia C., Powell, Luke L., Jamie, Gabriel A., Matthews, Thomas J., Johnson, Oscar, Brito, Guilherme R. R., Zyskowski, Kristof, Crates, Ross, Harvey, Michael G., Jurado Zevallos, Maura, Hosner, Peter A., Bradfer‐Lawrence, Tom, Maley, James M., Stiles, F. Gary, Lima, Hevana S., Provost, Kaiya L., Chibesa, Moses, Mashao, Mmatjie, Howard, Jeffrey T., Mlamba, Edson, Chua, Marcus A. H., Li, Bicheng, Gómez, M. Isabel, García, Natalia C., Päckert, Martin, Fuchs, Jérôme, Ali, Jarome R., Derryberry, Elizabeth P., Carlson, Monica L., Urriza, Rolly C., Brzeski, Kristin E., Prawiradilaga, Dewi M., Rayner, Matt J., Miller, Eliot T., Bowie, Rauri C. K., Lafontaine, René‐Marie, Scofield, R. Paul, Lou, Yingqiang, Somarathna, Lankani, Lepage, Denis, Illif, Marshall, Neuschulz, Eike Lena, Templin, Mathias, Dehling, D. Matthias, Cooper, Jacob C., Pauwels, Olivier S. G., Analuddin, Kangkuso, Fjeldså, Jon, Seddon, Nathalie, Sweet, Paul R., DeClerck, Fabrice A. J., Naka, Luciano N., Brawn, Jeffrey D., Aleixo, Alexandre, Böhning‐Gaese, Katrin, Rahbek, Carsten, Fritz, Susanne A., Thomas, Gavin H., Schleuning, Matthias (2022): AVONET: morphological, ecological and geographical data for all birds. Ecology Letters 25 (3): 581-597, DOI: 10.1111/ele.13898, URL: http://dx.doi.org/10.1111/ele.13898

Gut microbial communities play critical roles in the biological functions of their host, such as mediating nutrient absorption, digesting food components the host cannot, and offering protection against enteric pathogens. Extensive research on gut microbial communities has been conducted on mammals, including humans and rodents, but much less work has been done in birds. Furthermore, much of the research on host–microbe interactions make use of faecal samples and rectal/cloacal swabs as a proxy for intestinal samples, which can be difficult to obtain directly. However, little is known about the overlap between the microbial communities of the gut, faeces and swabs, which limits interpretability of results based on faecal samples and swabs. To address this gap in knowledge, we compared the microbiome from five sample types – proventriculus, small intestine, large intestine, cloacal swabs and faeces – across individual Zebra Finches Taeniopygia guttata housed in constant conditions with a standardized diet. We compared diversity and community composition through 16S rRNA gene sequencing. Our results show that microbial communities from both cloacal swabs and faeces were distinct from proventriculus and small intestinal samples, but generally indistinguishable from large intestinal samples, indicating that these non‐lethal samples may be useful proxies for large intestinal bacterial communities. Gaining insight into non‐invasive sampling techniques for passerines has implications for studies of gut microbial diversity and abundance in wild bird populations. Furthermore, reliable non‐lethal sampling is necessary for experiments where repeated sampling is required.

Learned traits, such as foraging strategies and communication signals, can change over time via cultural evolution. Using historical recordings, we investigate the cultural evolution of birdsong over nearly a 50-year period. Specifically, we examine the parts of white-crowned sparrow (Zonotrichia leucophrys nuttalli) songs used for mate attraction and territorial defense. We compared historical (early 1970s) recordings with contemporary (mid-2010s) recordings from populations within and near San Francisco, CA and assessed the vocal performance of these songs. Because birds exposed to anthropogenic noise tend to sing at higher minimum frequencies with narrower frequency bandwidths, potentially reducing one measure of song performance, we hypothesized that other song features, such as syllable complexity, might be exaggerated, as an alternative means to display performance capabilities. We found that vocal performance increased between historical and contemporary songs, with a larger effect size for urban songs, and that syllable complexity, measured as the number of frequency modulations per syllable, was historically low for urban males but increased significantly in urban songs. We interpret these results as evidence for males increasing song complexity and trilled performance over time in urban habitats, despite performance constraints from urban noise, and suggest a new line of inquiry into how environments alter vocal performance over time.

Many urban areas have elevated soil lead concentrations due to prior large-scale use of lead in products such as paint and automobile gasoline. This presents a potential problem for the growing numbers of wildlife living in urbanized areas as lead exposure is known to affect multiple physiological systems, including the nervous system, in vertebrate species. In humans and laboratory animals, low-level lead exposure is associated with neurological impairment, but less is known about how lead may affect the behavior of urban wildlife. We focused on the Northern Mockingbird Mimus polyglottos, a common, omnivorous North American songbird, to gain insights into how lead may affect the physiology and behavior of urban wildlife. We predicted that birds living in neighborhoods with high soil lead concentrations would (a) exhibit elevated lead concentrations in their blood and feathers, (b) exhibit lower body condition, (c) exhibit less diverse and consistent vocal repertoires, and (d) behave more aggressively during simulated conspecific territorial intrusions compared to birds living in neighborhoods with lower soil lead concentrations. Controlling for other habitat differences, we found that birds from areas of high soil lead had elevated lead concentrations in blood and feathers, but found no differences in body condition or vocal repertoires. However, birds from high lead areas responded more aggressively during simulated intrusions. These findings indicate that sub-lethal lead exposure may be common among wildlife living in urban areas, and that this exposure is associated with increased aggression. Better understanding of the extent of the relationship between lead exposure and aggression and the consequences this could have for survival and reproduction of wild animals are clear priorities for future work in this and other urban ecosystems.

Made available in DSpace on 2022-04-28T19:42:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 The family Thamnophilidae is a species-rich Neotropical radiation of passerine birds. Current classification of its 235 species is mostly based on morphological similarities, but recent studies integrating comprehensive phenotypic and phylogenetic data have redefined taxonomic limits of several taxa. Here, we assess generic relationships of Herpsilochmus, Sakesphorus, Thamnophilus, Biatas, and Dysithamnus using DNA sequences from the mitochondrion, nuclear exons, and ultraconserved elements, with further attention to interspecific relationships within Herpsilochmus. We show that Herpsilochmus and Sakesphorus are not monophyletic. We resolve Herpsilochmus sellowi as a deep-branch sister to the monotypic genus Biatas and Sakesphorus cristatus as sister to a clade comprising Herpsilochmus sensu stricto and Dysithamnus. These results are consistent across loci, obtained via concatenation and coalescent-based analyses, and supported by likelihood-ratio tests of the distribution of our sampled coalescent histories. The phenotypic distinctiveness of both H. sellowi and Biatas argues against merging them into a single genus. Because no generic name is available for H. sellowi, we describe a monotypic genus. The polyphyly of Sakesphorus warrants recognition of the available generic name Sakesphoroides for the distinctive and monotypic S. cristatus. Furthermore, we recover 6 well-supported species groups within Herpsilochmus sensu stricto. Within the context of the family as a whole, the ubiquity of long terminal branches representing monotypic genera points to extinction events among ancestors of these lineages. We suggest that retention of ancestral characters or random genetic drift coupled with extensive extinction could explain the high degree of morphological and ecological similarity across these taxa, but we highlight the potential role of the environment in driving adaptive phenotypic convergence. Finally, our results send a cautionary message against the blind use of phylogenies containing imputed data based on taxonomy due to the increasingly frequent mismatches between traditional taxonomic classification and molecular phylogenies. LAY SUMMARY We conduct phylogenomic analyses to infer generic relationships of Herpsilochmus, Sakesphorus, Thamnophilus, Biatas, and Dysithamnus. Using thousands of ultraconserved elements, exons, and mitochondrial DNA, we consistently show that the genus Herpsilochmus is not monophyletic because H. sellowi is a sister of the monotypic species Biatas nigropectus. Because the phenotypic distinctiveness of H. sellowi and B. nigropectus argues against merging them into a single genus and there is no available generic name for H. sellowi, we describe a monotypic genus for this species. We also found polyphyly of the genus Sakesphorus, warranting recognition of the available generic name Sakesphoroides for Sakesphorus cristatus. Our results provide a robust framework for downstream analyses of biogeographic and phenotypic evolution of Herpsilochmus antwrens and allies. This study adds to the increasing body of literature documenting the mismatch between traditional avian taxonomic classifications based on external morphology and evolutionary histories traced by modern genetic tools. Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology Harvard University Seção de Aves Museu de Zoologia Universidade de São Paulo Museum of Natural Science and Department of Biological Sciences Louisiana State University Departamento de Zoologia Universidade Federal do Paraná Centro Politécnico Programa de Pós-Graduação em Zoologia Departamento de Zoologia Universidade Federal do Paraná Centro Politécnico Departamento de Ciências Biológicas e Ambientais Instituto de Biociências Universidade Estadual Paulista Mater Natura - Instituto de Estudos Ambientais Gund Institute for Environment The University of Vermont Rubenstein School of Environment and Natural Resources The University of Vermont Departamento de Zoologia Universidade Federal de Pernambuco Coordenação de Zoologia Museu Paraense Emílio Goeldi Finnish Museum of Natural History University of Helsinki Department of Ecology and Evolutionary Biology University of Tennessee Departamento de Ciências Biológicas e Ambientais Instituto de Biociências Universidade Estadual Paulista

Noise pollution is an unprecedented evolutionary pressure on wild animals that can lead to alteration of stress hormone levels and changes in foraging behavior. Both corticosterone and feeding behavior can have direct effects on gut bacteria, as well as indirect effects through changes in gut physiology. Therefore, we hypothesized that exposure to noise will alter gut microbial communities via indirect effects on glucocorticoids and foraging behaviors. We exposed captive white-crowned sparrows to city-like noise and measured each individuals' corticosterone level, food intake, and gut microbial diversity at the end of four treatments (acclimation, noise, recovery, and control) using a balanced repeated measures design. We found evidence that noise acts to increase corticosterone and decrease food intake, adding to a growing body of research indicating noise exposure affects stress hormone levels and foraging behaviors. We also found evidence to support our prediction for a causal, positive relationship between noise exposure and gut microbial diversity, such that birds had higher measures of alpha diversity during noise exposure. These results help to explain previous findings that urban, free-living white-crowned sparrows have higher bacterial richness than rural sparrows. However, noise appeared to act directly on the gut microbiome or, more likely, through an unmeasured variable, rather than through indirect effects via corticosterone and food intake. Altogether, our study indicates that noise affects plasma corticosterone, feeding behavior, and the gut microbiome in a songbird and raises new questions as to the mechanism linking noise exposure to gut microbial diversity.

Species-specific vocalizations can act as a reproductive isolating mechanism between closely related populations. We analyzed vocal differences between 2 hybridizing species of sex-role reversed polyandrous shorebirds, the Northern Jacana (Jacana spinosa) and Wattled Jacana (J. jacana). We found that Northern Jacana calls have higher fundamental frequency and peak frequency than Wattled Jacana calls. We also compared calls between females and males, as both jacana species are sex-role reversed and females compete for male mates. Males produce calls with a higher fundamental and peak frequency and shorter notes than females. These results suggest that vocal differences between Northern and Wattled jacanas have the potential to act as a behavioral mediator of interspecific interactions, and that sex differences in vocalizations may relate to sex-role reversal in territorial defense and mate attraction.

Urbanization is one of the most extreme forms of land transformation and results in changes to ecosystems and species compositions. As a result, there are strong directional selection pressures compared to nearby rural areas. Despite a surge in research on the different selection pressures on acoustic communication in urban and rural areas, there has been comparatively little investigation into traits involved with visual communication. We measured the plumage of museum specimens of white-crowned sparrows (Zonotrichia leucophrys) from urban and adjacent rural habitats in San Francisco, CA, to assess the effects of divergent habitats on plumage. We found significant differences in dorsal plumage, but not crown plumage, between urban and rural populations that have been diverging over the past 100 years. Urban birds have increasingly darker and duller dorsal plumage, whereas rural birds in adjacent areas have plumage with richer hues and more color complexity. Our findings suggest a newly observed adaptation to urban environments by native species and suggest that many traits, in addition to acoustic signals, may be changing in response to urban selection pressures. Additional collections in urban areas are needed to explore likely divergences in plumage coloration between urban and rural environments.

Diversity does not drive speciation The role of the environment in the origin of new species has long been debated. Harvey et al. examined the evolutionary history and species diversity of suboscine birds in the tropics (see the Perspective by Morlon). Contrary to expectations that the tropics have higher rates of speciation, the authors observed that higher and more constant speciation rates occur in harsh environments relative to the tropics. Thus, for this group of birds, diversification in temperate to Arctic regions followed by the movement and retention of species in the tropics results in their higher local levels of species diversity. Science , this issue p. 1343 ; see also p. 1268

Human activity around the globe is a growing source of selection pressure on animal behavior and communication systems. Some animals can modify their vocalizations to avoid masking from anthropogenic noise. However, such modifications can also affect the salience of these vocalizations in functional contexts such as competition and mate choice. Such is the case in the well-studied Nuttall's white-crowned sparrow (Zonotrichia leucophrys nuttalli), which lives year-round in both urban San Francisco and nearby rural Point Reyes. A performance feature of this species' song is salient in territorial defense, such that higher performance songs elicit stronger responses in simulated territorial intrusions; but songs with lower performance values transmit better in anthropogenic noise. A key question then is whether vocal performance signals male quality and ability to obtain high quality territories in urban populations. We predicted white-crowned sparrows with higher vocal performance will be in better condition and will tend to hold territories with lower noise levels and more species-preferred landscape features. Because white-crowned sparrows are adapted to coastal scrub habitats, we expect high quality territories to contain lower and less dense canopies, less drought, more greenness, and more flat open ground for foraging. To test our predictions, we recorded songs and measured vocal performance and body condition (scaled mass index and fat score) for a set of urban and rural birds (N = 93), as well as ambient noise levels on their territories. Remote sensing metrics measured landscape features of territories, such as drought stress (NDWI), greenness (NDVI), mean canopy height, maximum height, leaf area density (understory and canopy), slope, and percent bare ground for a 50 m radius on each male territory. We did not find a correlation between body condition and performance but did find a relationship between noise levels and performance. Further, high performers held territories with lower canopies and less dense vegetation, which are species-preferred landscape features. These findings link together fundamental aspects of sexual selection in that habitat quality and the quality of sexually selected signals appear to be associated: males that have the highest performing songs are defending territories of the highest quality.

Vocal learning has evolved independently in several lineages. This complex cognitive trait is commonly treated as binary: species either possess or lack it. This view has been a useful starting place to examine the origins of vocal learning, but is also incomplete and potentially misleading, as specific components of the vocal learning program - such as the timing, extent and nature of what is learned - vary widely among species. In our review we revive an idea first proposed by Beecher and Brenowitz (2005) by describing six dimensions of vocal learning: (1) which vocalizations are learned, (2) how much is learned, (3) when it is learned, (4) who it is learned from, (5) what is the extent of the internal template, and (6) how is the template integrated with social learning and innovation. We then highlight key examples of functional and mechanistic work on each dimension, largely from avian taxa, and discuss how a multi-dimensional framework can accelerate our understanding of why vocal learning has evolved, and how brains became capable of this important behaviour.

The environment can impose constraints on signal transmission properties such that signals should evolve in predictable directions (Sensory Drive Hypothesis). However, behavioral and ecological factors can limit investment in more than one sensory modality leading to a trade-off in use of different signals (Transfer Hypothesis). In birds, there is mixed evidence for both sensory drive and transfer hypothesis. Few studies have tested sensory drive while also evaluating the transfer hypothesis, limiting understanding of the relative roles of these processes in signal evolution. Here, we assessed both hypotheses using acoustic and visual signals in male and female antwrens (Thamnophilidae), a species-rich group that inhabits diverse environments and exhibits behaviors, such as mixed-species flocking, that could limit investment in different signal modalities. We uncovered significant effects of habitat (sensory drive) and mixed-species flocking behavior on both sensory modalities, and we revealed evolutionary trade-offs between song and plumage complexity, consistent with the transfer hypothesis. We also showed sex- and trait-specific responses in visual signals that suggest both natural and social selection play an important role in the evolution of sexual dimorphism. Altogether, these results support the idea that environmental (sensory drive) and behavioral pressures (social selection) shape signal evolution in antwrens.

Recent studies using molecular phylogenetics have provided new insight into the composition of and relationships among species in the avian tribe Xolmiini. Key findings include the paraphyly of Xolmis, including the exclusion of X. dominicanus from the Xolmiini, and the apparent paraphyly of Muscisaxicola. We provide a revised classification of the Xolmiini, including a new genus for Muscisaxicola fluviatilis, based on the recent phylogenetic results.

In Focus: Seress, G, Sandor, K, Evans, KL, Liker, A. (2020) Food availability limits avian reproduction in the city: An experimental study on great tits Parus major . Journal of Animal Ecology. 89. Animals in urban areas face a multitude of stressors, but how each stressor impacts survival and fitness can be difficult to disentangle. We need experimental manipulations of suspected stressors to examine causal relationships with traits of free-living urban and rural animals. In this issue, Seress and colleagues take on an intensive experimental approach to test whether one potential stressor-limited natural food sources in cities-can explain reduced avian reproductive success in urban areas. They employ a full factorial design, including both food supplemented and control broods in both urban and forest great tit Parus major populations. The findings are clear. Reduced food availability is the key factor limiting urban offspring growth and survival, at least in this well-studied species. Indeed, the extra insects fed to urban chicks greatly reduced the significant differences in survival rates and body sizes between urban and forest broods. The findings are also sobering. Urban insect populations would need to more than double to erase differences in reproductive success between urban and rural bird populations, an unlikely outcome with the ever-increasing urbanization of habitats.

Habitats are changing rapidly around the globe and urbanization is one of the primary drivers. Urbanization changes food availability, environmental stressors, and the prevalence of disease for many species. These changes can lead to divergence in phenotypic traits, including behavioral, physiological, and morphological features between urban and rural populations. Recent research highlights that urbanization is also changing the gut microbial communities found in a diverse group of host species. These changes have not been uniform, leaving uncertainty as to how urban habitats are shaping gut microbial communities. To better understand these effects, we investigated the gut bacterial communities of White-Crowned Sparrow (Zonotrichia leucophrys) populations along an urbanization gradient in the San Francisco Bay area. We examined how gut bacterial communities vary with the local environment and host morphological characteristics. We found direct effects of environmental factors, including urban noise levels and territory land cover, as well as indirect effects through body size and condition, on alpha and beta diversity of gut microbial communities. We also found that urban and rural birds' microbiomes differed in which variables predicted their diversity, with urban communities driven by host morphology, and rural communities driven by environmental factors. Elucidating these effects provides a better understanding of how urbanization affects wild avian physiology.

Heat waves are rapidly increasing in frequency and length around the globe. These periods of elevated temperatures are inducing extreme thermal stress in many organisms. One dramatic result of heat waves is mass mortality events, notably in birds. Although much attention is given to lethal events, little is known about how more common sublethal temperatures affect behaviour, especially in endotherms. For example, male song sparrows, Melospiza melodia atlantica, sing at lower rates at higher temperatures. We hypothesized that simulated heat waves may also reduce the ability of females to discriminate between sexual signals. We tested this hypothesis by quantifying whether female zebra finches, Taeniopygia guttata, responded more to conspecific song or heterospecific song while at their typical housing temperature compared to temperatures above their upper critical temperature. We collected data on how often the birds selected conspecific over heterospecific songs and how much effort the birds invested in sampling those songs using a matched-pairs design. During housing temperature trials, females preferred conspecific song compared to heterospecific song. In contrast, females no longer showed a preference for conspecific song at temperatures above their upper critical limit, although the birds invested similar effort in sampling songs in both treatments. Our findings provide the first experimental evidence that high temperatures affect female preference for a mating signal in an endotherm. Our results highlight the need for future work to investigate this overlooked effect of climate change on endotherms. Because thermoregulatory processes are phylogenetically conserved, our results generate useful predictions for future studies of heat wave effects on mating behaviours in endotherms.

We studied the phylogeny, biogeography, and diversification of suboscine passerines in the genus Scytalopus (Rhinocryptidae), a widespread, species-rich, and taxonomically challenging group of Neotropical birds. We analyzed nuclear (exons, regions flanking ultraconserved elements) and mitochondrial (ND2) DNA sequence data for a taxonomically and geographically comprehensive sample of specimens collected from Costa Rica to Patagonia and Brazil. We found that Scytalopus is a monophyletic group sister to Eugralla and consists of 3 main clades roughly distributed in (1) the Southern Andes, (2) eastern Brazil, and (3) the Tropical Andes and Central America. The clades from the Southern Andes and eastern Brazil are sister to each other. Despite their confusing uniformity in plumage coloration, body shape, and overall appearance, rates of species accumulation through time in Scytalopus since the origin of the clade in the Late Miocene are unusually high compared with those of other birds, suggesting rapid non-adaptive diversification in the group. We attribute this to their limited dispersal abilities making them speciation-prone and their occurrence in a complex landscape with numerous barriers promoting allopatric differentiation. Divergence times among species and downturns in species accumulation rates in recent times suggest that most speciation events in Scytalopus predate climatic oscillations of the Pleistocene. Our analyses identified various cases of strong genetic structure within species and lack of monophyly of taxa, flagging populations which likely merit additional study to clarify their taxonomic status. In particular, detailed analyses of species limits are due in S. parvirostris, S. latrans, S. speluncae, the S. atratus complex, and the Southern Andes clade.

Premise of research. The evolution of lineages on continental edaphic islands has been an important determinant of diversification. To understand the complexities of continental edaphic diversifica...

Sexual signals that are physically limited can be reliable indicators of quality or motivation in male–male competition. One such example of a motor constraint in birds is the production of repeated notes, which are limited in the frequency bandwidth and trill rate at which notes can be produced, such that it is difficult to produce wide-bandwidth notes at fast rates. How well birds maximize frequency bandwidth and trill rate is one measure of vocal performance, commonly referred to as ‘vocal deviation’. In theory, fast songs with narrow bandwidths and slow songs with wide bandwidths should have similar values of vocal deviation. In many species, males respond to variation in vocal deviation, supporting the notion that it is a sexually selected signal. However, most studies test only one of these components, either trill rate or bandwidth, rather than both individually, when testing receiver response to vocal deviation. Therefore, a question remains as to whether songs with equivalent values of vocal deviation (e.g. fast songs with narrow bandwidths and slow songs with wide bandwidths) elicit similar levels of response from receivers. We tested whether receivers respond specifically to the trade-off between trill rate and bandwidth (i.e. vocal deviation) or only to variation in one of the component parts. Using territorial playback experiments with wild male white-crowned sparrows, Zonotrichia leucophrys, we found that males approached high-performance songs (fast trill, wide bandwidth) more closely than they did lower-performance songs (fast trill, narrow bandwidth; slow trill, wide bandwidth) and they did so regardless of whether performance varied because of differences in trill rate or bandwidth. Furthermore, we found that males gave similar responses to songs of similar vocal deviation. Our results empirically support the hypothesis that receivers respond specifically to the physical limitation on the production of repeated notes.

Vocal communication in songbirds is important for aggressive signaling, such that an honest signal allows receivers to assess a competitor's qualities. One aspect of song that conspecifics may assess is vocal performance. An example of vocal performance is how well an individual performs the trade-off between trill rate and bandwidth in production of repeated notes. This type of vocal performance (vocal deviation) is thought to be an honest signal because a male's ability to maximize both bandwidth and trill rate is limited by motor constraints on sound modification. Further, how well a male can repeat this trade-off may provide receivers with information about the signaler, and a male's own level of vocal performance can affect the strength of response to high-performance songs. We tested whether males assess each other based on vocal performance in an important model species, the White-crowned Sparrow (Zonotrichia leucophrys). We show that male White-crowned Sparrows respond more strongly to hi...

Species-specific vocalizations can act as a reproductive isolating mechanism between closely related populations. We analyzed vocal divergence between two hybridizing species of sex-role reversed polyandrous shorebirds, the Northern Jacana (Jacana spinosa) and Wattled Jacana (Jacana jacana). We found that J. spinosa calls have higher peak frequency and fundamental frequency than J. jacana calls. We also compared calls between males and females, as both jacana species are sex-role reversed and females compete for male mates. Males produce calls with a higher peak frequency, exhibit shorter note lengths and emit a greater number of notes within a calling bout than females, which could relate to mate attraction. These results suggest that vocal divergence could act as a behavioral barrier to limit hybridization between the species and vocalizations may function differently between male and female jacanas.

We studied the phylogeny, biogeography and diversification of suboscine birds in the genusScytalopus(Rhinocryptidae), a widespread, speciose, and taxonomically challenging group of Neotropical birds. We analyzed nuclear (exons, regions flanking ultraconserved elements) and mitochondrial (ND2) DNA sequence data for a taxonomically and geographically comprehensive sample of specimens collected from Costa Rica to Patagonia and eastern Brazil. We found thatScytalopusis a monophyletic group sister toEugralla, and consists of three main clades roughly distributed in (1) the Southern Andes, (2) eastern Brazil, and (3) the Tropical Andes and Central America. The clades from the Southern Andes and Eastern Brazil are sister to each other. Despite their confusing overall uniformity in plumage coloration, body shape and overall appearance, rates of species accumulation through time inScytalopussince the origin of the clade in the Late Miocene are unusually high compared to those of other birds, suggesting rapid non-adaptive diversification in the group which we attribute to their limited dispersal abilities making them speciation-prone and their occurrence in a complex landscape with numerous barriers promoting allopatric differentiation. Divergence times among species and downturns in species accumulation rates in recent times suggest that most speciation events inScytalopuspredate climatic oscillations of the Pleistocene. Our analyses identified various cases of strong genetic structure within species and lack of monophyly of taxa, flagging populations which likely merit additional study to establish their taxonomic status. In particular, detailed analyses of species limits are due inS. parvirostris, S. latrans, S. speluncae, theS. atratuscomplex, and the Southern Andes clade.

In Focus: Da Silva, A., & Kempenaers, B. (2017). Singing from North to South: Latitudinal variation in timing of dawn singing under natural and artificial light conditions. Journal of Animal Ecology, 86, 1286–1297. doi: 10.1111/1365-2656.12739 Satellite images of the world at night show bright dots connected by glowing lines crisscrossing the globe. As these connect-the-dots become brighter and expand into more and more remote regions, much of the flora and fauna of the world are experiencing evolutionarily unprecedented levels of light at night. Light cues are essential to most physiological and behavioural processes, and so the need to measure the effects of light pollution on these processes is critical. In this issue, Da Silva and Kempenaers take on this task using an important reproductive behaviour in songbirds—dawn song. The geographic, temporal and taxonomic breadth of sampling in this study allows for a close examination of a potentially complex interaction between light pollution and natural variation in the behaviour of dawn singing across latitude, season and species. Their extensive dataset highlights complexity in how songbirds respond to light pollution. Although light pollution has a strong effect on the timing of dawn song, not all songbirds respond the same way to light pollution, and the effects of light pollution vary with changes in natural light levels. Early dawn singers show more flexibility in the timing of dawn song across the season and across latitudes than late dawn singers, and also appear less affected by light pollution at high latitudes than are late dawn singers. These findings suggest that not all songbirds are responding to artificial continuous daylight as they do to natural continuous daylight, highlighting the general need to measure the fitness effects of light pollution.

The Neotropics show a wealth of distributional patterns shared by many co-distributed species. A distinctive pattern is the so-called “circum-Amazonian distribution,” which is observed in species that do not occur in Amazonia but rather along a belt of forested habitats spanning south and east of Amazonia, the Andean foothills, and often into the Venezuelan Coastal Range and the Tepuis. Although this pattern is widespread across animals and plants, its underlying biogeographic mechanisms remain poorly understood. The Variable Antshrike (Thamnophilus caerulescens) is a sexually dimorphic suboscine passerine that exhibits extreme plumage variation and occurs along the southern portion of the circum-Amazonian belt. We describe broad-scale phylogeographic patterns of T. caerulescens and assess its demographic history using DNA sequences from the mitochondrion and ultraconserved elements (UCEs). We identified three genomic clusters: a) northern Atlantic Forest; b) southeastern Cerrado and central-southern Atlantic Forest, and c) Chaco and Andes. Our results were consistent with Pleistocene divergence followed by gene flow, mainly between the latter two clusters. There were no genetic signatures of rapid population expansions or bottlenecks. The population from the northern Atlantic Forest was the most genetically divergent group within the species. The demographic history of T. caerulescens was probably affected by series of humid and dry periods throughout the Quaternary that generated subtle population expansions and contractions allowing the intermittent connection of habitats along the circum-Amazonian belt. Recognizing the dynamic history of climate-mediated forest expansions, contractions, and connections during the South American Pleistocene is central toward a mechanistic understanding of circum-Amazonian distributions.

Rapid diversification limits our ability to resolve evolutionary relationships and examine diversification history, as in the case of the Neotropical cotingas. Here we present an analysis with complete taxon sampling for the cotinga genera Lipaugus and Tijuca, which include some of the most range-restricted (e.g., T. condita) and also the most widespread and familiar (e.g., L. vociferans) forest birds in the Neotropics. We used two datasets: (1) Sanger sequencing data sampled from eight loci in 34 individuals across all described taxa and (2) sequence capture data linked to 1,079 ultraconserved elements and conserved exons sampled from one or two individuals per species. Phylogenies estimated from the Sanger sequencing data failed to resolve three nodes, but the sequence capture data produced a well-supported tree. Lipaugus and Tijuca formed a single, highly supported clade, but Tijuca species were not sister and were embedded within Lipaugus. A dated phylogeny confirmed Lipaugus and Tijuca diversified rapidly in the Miocene. Our study provides a detailed evolutionary hypothesis for Lipaugus and Tijuca and demonstrates that increasing genomic sampling can prove instrumental in resolving the evolutionary history of recent radiations.

A female’s cognitive ability may influence her mate preferences through various mechanisms. These mechanisms include the direct effect of cognitive ability on the information-processing skills used during mate choice, and the indirect effect of cognitive ability on quality when females mate assortatively. Here, we examined whether the ability to learn a novel foraging task, a cognitive skill which has been associated with reproductive success in other capacities, was correlated with song preferences in female zebra finches (Taeniopygia guttata). Female preferences were measured in an operant testing chamber where hops on a perch triggered song playback. Females were given the choice of (1) conspecific vs. heterospecific song and (2) high-quality male vs. low-quality male conspecific song. We found that female performance on the novel foraging task was positively correlated with preference for conspecific song, but not with preference for high-quality male song. Instead, female mass was positively correlated with preference for high-quality male song, potentially signifying that female mass is a stronger predictor of female quality in assortative mating than female cognitive performance. Female mass and cognitive performance were unrelated. Our results suggest that the particular traits of a female that affect conspecific preference do not necessarily affect preference for high-quality males.

Significance Our understanding of the factors that affected the diversification of passerines, the most diverse and widespread bird order (Passeriformes), is limited. Here, we reconstruct passerine evolutionary history and produce the most comprehensive time-calibrated phylogenetic hypothesis of the group using extensive sampling of the genome, complete sampling of all passerine families, and a number of vetted fossil calibration points. Our phylogenetic results refine our knowledge of passerine diversity and yield divergence dates that are consistent with the fossil record, and our macroevolutionary analyses suggest that singular events in Earth history, such as increases in Cenozoic global temperature or the colonization of new continents, were not the primary forces driving passerine diversification., Avian diversification has been influenced by global climate change, plate tectonic movements, and mass extinction events. However, the impact of these factors on the diversification of the hyperdiverse perching birds (passerines) is unclear because family level relationships are unresolved and the timing of splitting events among lineages is uncertain. We analyzed DNA data from 4,060 nuclear loci and 137 passerine families using concatenation and coalescent approaches to infer a comprehensive phylogenetic hypothesis that clarifies relationships among all passerine families. Then, we calibrated this phylogeny using 13 fossils to examine the effects of different events in Earth history on the timing and rate of passerine diversification. Our analyses reconcile passerine diversification with the fossil and geological records; suggest that passerines originated on the Australian landmass ∼47 Ma; and show that subsequent dispersal and diversification of passerines was affected by a number of climatological and geological events, such as Oligocene glaciation and inundation of the New Zealand landmass. Although passerine diversification rates fluctuated throughout the Cenozoic, we find no link between the rate of passerine diversification and Cenozoic global temperature, and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents. Taken together, these results suggest more complex mechanisms than temperature change or ecological opportunity have controlled macroscale patterns of passerine speciation.

Mating behavior between recently diverged species in secondary contact can impede or promote reproductive isolation. Traditionally, researchers focus on the importance of female mate choice and male-male competition in maintaining or eroding species barriers. Although female-female competition is widespread, little is known about its role in the speciation process. Here, we investigate a case of interspecific female competition and its influence on patterns of phenotypic and genetic introgression between species. We examine a hybrid zone between sex-role reversed, Neotropical shorebird species, the northern jacana (Jacana spinosa) and wattled jacana (J. jacana), in which female-female competition is a major determinant of reproductive success. Previous work found that females of the more aggressive and larger species, J. spinosa, disproportionately mother hybrid offspring, potentially by monopolizing breeding territories in sympatry with J. jacana. We find a cline shift of female body mass relative to the genetic center of the hybrid zone, consistent with asymmetric introgression of this competitive trait. We suggest that divergence in sexual characteristics between sex-role reversed females can influence patterns of gene flow upon secondary contact, similar to males in systems with more typical sex roles.