Songbird Species Research Articles

The Temporal organization of learned vocal behavior is predicted by species rather than experience.

Birdsong is hierarchically organized in time, like speech and other communication behaviors. Syllables are produced in sequences to form song motifs and bouts. While syllables are copied from tutors, the factors that determine song temporal organization, including syllable sequencing (syntax), are unknown. Here, we tested the roles of learning and species genetics in song organization. We manipulated juvenile song experience and genetics in three species of estrildid finches (zebra finches: Taeniopygia guttata castanotis; long-tailed finches: Poephila acuticauda; Bengalese finches: Lonchura striata var. domestica). We analyzed the adult songs of male birds that were: 1) tutored by conspecifics; 2) untutored; 3) tutored by heterospecifics; and 4) genetic hybrids. Song macrostructure, syllable sequencing, and syllable timing were quantified and compared within and across species. Results showed that song organization was consistent within a species and differed across species, regardless of experience. Temporal features did not differ between tutored and untutored birds of the same species. The songs of birds tutored by other species were composed of heterospecific syllables produced in sequences typical of conspecific song. The songs of genetic hybrids showed the organization of both parental species, despite the fact that only males sing. Results indicate that song organization is predicted by species rather than experience.Significance statement Like speech, birdsong is a complex and learned behavior that is hierarchically organized in time. Previous work suggests that species identity influences song temporal organization. We tested the roles of genetics and learning in song organization in three songbird species and genetic hybrids. Birds were either tutored, untutored, or tutored by another species. Results showed that song organization was consistent within a species and differed across species, regardless of experience. Our findings suggest that the organization of behavioral sequences is shaped by both genes and experience, with the influence of experience acting at the level of units in a sequence and the influence of species genetics acting at the level of sequence organization.

Meaning and Mechanisms of Birdsong: Inspiration for Pneumology

In contrast to humans, the location where sound is produced in birds is not the larynx, but rather the so-called "vocal box" (scientific term "Syrinx"). In some species the syrinx is located at the bifurcation point of the trachea into the two main bronchi (tracheal vocal head), while in some in the main bronchi (bronchial vocal head). During inspiration, part of the air flows into the lungs, and the part needed for singing flows into the air sacs adjacent to the lungs. During expiration, air leaves the air sacs and flows through the syrinx, where the song is created. When birds sing in two voices at the same time, individual sequences are formed simultaneously in the right and left parts of the syrinx.The song analysis is based on spectrograms (so-called sonagrams), which graphically represent the frequency spectrum of bird song.The song consists of one or more verses, which in turn consist of the variable or constant sequence of motives or syllables. Some songbirds have an enormous repertoire of syllables and verses (max. up to 7000 verses per day). In addition to singing, most bird species also have much simpler begging, contact, threatening, flight, alarm and copulation calls.Male birds sing primarily for two reasons: 1. They use song to woo a potential partner. This song provides the females with important information about the applicant's performance and health. 2. Singing serves to defend the territory.In around 40 % of songbird species, females also sing. Pairs of some species sing in perfect synchronization.A number of songbirds imitate both the voices of other songbirds and ambient noises, and many songbirds have regional dialects.Song development depends on genetics and other factors such as the environment, metabolism and hormonal influences. It proceeds step by step and initially includes relatively primitive sequences (so-called "subsongs"), then leads through more complex intermediate forms ("plastic songs") and finally to the completed singing pattern ("full songs").Young birds learn the song of their species at a time when they are not yet singing themselves, often as nestlings aged 10 to 50 days from older members of the species, usually from their fathers.The song of young birds develops, based on the template of adult song, in a network of sensory-motor neurons in the forebrain.Songbirds, especially the zebra finch, currently offer the best model for the neural basis of human language learning. In birds, the so-called "High Vocal Center" orchestrates all brain regions relevant to songs, with the neural control of song being sensitive to sex hormones.

Conspicuous Animals Remain Alert When Under Cover but Do Not Differ in the Temporal Course of Vigilance from Less Conspicuous Species.

Conspicuousness increases the risk of predation. One strategy to reduce this risk is to increase vigilance. We investigated the frequency of head movements as a measure of vigilance at waterholes in two related songbird species that differed in their conspicuousness: the Gouldian finch and the long-tailed finch. While both species showed a high frequency of head movements (high vigilance) when sitting in an open tree, the more colourful Gouldian finch remained more vigilant than the less conspicuous long-tailed finch when sitting under cover. Moreover, juvenile Gouldian finches had similar vigilance levels than adults; whereas, juveniles of the long-tailed finch were less vigilant, possibly because of staying in the family group. Furthermore, both species showed a similar temporal course of vigilance with a fast decrease in vigilance after landing in the tree, which was affected by group size. Single individuals had much higher vigilance than groups of birds. Finally, vigilance was higher at small waterholes. The results show that conspicuousness, uncertainty when arriving at waterholes, and higher perceived risk at small waterholes increased vigilance.

Uncovering Breeding Habitat Use of an Uncommon Songbird in Pennsylvania Using Large Scale Acoustic Data

ABSTRACTThe Canada Warbler (Cardellina canadensis) population has declined by over 60% across its range since 1966. Knowledge of breeding habitat use is crucial to the conservation of songbird species but is missing for significant portions of the breeding range of the Canada Warbler's genetically distinct eastern population. We used a large‐scale deployment of autonomous recording units (ARUs) to record Canada Warbler song across north‐central and southwestern Pennsylvania. We deployed ARUs at 664 locations in forested ecosystems, setting them to record for 2 h each morning from mid‐May to mid‐June. We used classifier‐assisted listening to detect Canada Warbler song and generate detection histories. Our occupancy models revealed six significant habitat associations. We highlight forest conditions that can be targeted for the conservation of steeply declining eastern Canada Warbler populations. Our study is an example of the gains in statistical power allowed by ARUs and machine learning methods.

Growing up with chronic traffic noise exposure leads to transient but not long-term noise tolerance in a songbird.

Noise pollution is on the rise worldwide. An unresolved issue regarding the mitigation of noise pollution is whether and at which timescales animals may adapt to noise pollution. Here, we tested whether continuous highway noise exposure perinatally and during juvenile development increased noise tolerance in a songbird, the zebra finch (Taeniopygia castanotis). Breeding pairs were exposed to highway noise recordings from pre-egg-laying until their offspring reached subadulthood. Subsequently, offspring were tested for noise tolerance both as subadults and adults in a spatial preference test, where birds could choose to enter aviaries with different levels of highway noise. Unlike control birds that preferentially chose the quiet aviaries, noise-reared birds exhibited no spatial preferences for quiet in the first test. However, when the experimental birds were retested after two months without noise exposure, they now avoided the previously tolerated noise levels and preferred the quieter aviary. The increased noise tolerance observed directly after the release from the noise treatment was thus only transient. Growing up with chronic highway noise exposure did thus not increase subjects' noise tolerance, meaning that at least in this songbird species, adaptation to noise pollution is unlikely to arise on a developmental time scale.

A complex acoustical environment during development enhances auditory perception and coding efficiency in the zebra finch.

Sensory experience during development has lasting effects on perception and neural processing. Exposing juvenile animals to artificial stimuli influences the tuning and functional organization of the auditory cortex, but less is known about how the rich acoustical environments experienced by vocal communicators affect the processing of complex vocalizations. Here, we show that in zebra finches (Taeniopygia guttata), a colonial-breeding songbird species, exposure to a naturalistic social-acoustical environment during development has a profound impact on auditory perceptual behavior and on cortical-level auditory responses to conspecific song. Compared to birds raised by pairs in acoustic isolation, male and female birds raised in a breeding colony were better in an operant discrimination task at recognizing conspecific songs with and without masking colony noise. Neurons in colony-reared birds had higher average firing rates, selectivity, and discriminability, especially in the narrow-spiking, putatively inhibitory neurons of a higher-order auditory area, the caudomedial nidopallium (NCM). Neurons in colony-reared birds were also less correlated in their tuning and more efficient at encoding the spectrotemporal structure of conspecific song, and better at filtering out masking noise. These results suggest that the auditory cortex adapts to noisy, complex acoustical environments by strengthening inhibitory circuitry, functionally decoupling excitatory neurons while maintaining overall excitatory-inhibitory balance.Significance Statement The statistics of the sensory inputs animals experience during postnatal development shape cortical circuits and their functional properties, but most studies examining experience-dependent plasticity in the auditory system has employed artificial stimuli with limited relevance to acoustic communication. Here, we examined how the natural social-acoustical environment experienced by zebra finches, a social songbird that breeds in large colonies, influences the development of auditory perception and the underlying auditory cortical circuits. Compared to birds raised in a more impoverished environment, colony-reared birds were better at recognizing songs of other zebra finches and had higher firing rates in the avian homolog to auditory cortex, along with changes to functional connectivity that resulted in more efficient and robust coding of conspecific song.

Distribution of Bird Communities and Habitat Corridor Composition Shaped by Environmental Factors in Urbanized Landscapes: A Case Study in Beijing, China

Urban biodiversity is crucial for ecological security, balance, and important for fostering awareness on human-nature interconnectedness among the public. The diversity of birds, as an urban ecosystem indicator, reflects ecosystem services and is impacted by urban development. To explore the impacts of urbanization on bird diversity, stratified to songbirds, terrestrial birds, climbers, swimming birds, wading birds, and raptors, we specifically investigated the existing and potential distributions of selected bird species, analyzed different contributions of environmental factors, and compared these with urban biodiversity conservation policies. We used bird records from the China Birdwatching Record Center (over 1400 species of birds for querying) and remotely-sensed landcover data, based on the MaxEnt model, to analyze bird spatial distribution characteristics and potential habitat corridors throughout Beijing. The results showed that: (1) Songbirds and terrestrial birds were predominantly concentrated in water areas in urban areas. Wading birds, climbers, swimming birds, and raptors were gathered in forest-covered areas, near wetlands and farmland in suburban areas. Projections indicated that the raptor species Common Kestrel (Falco tinnunculus) showed a notable shift toward urban cores. (2) Among climbers, Gray-headed Pygmy Woodpecker (Dendrocopos canicapillus) occupied the highest proportion of high-quality habitats (10.34%), contrasting with the representative songbird species Blackbird (Turdus merula) at 1.38%, which demonstrated adaptability to urban environments. Critical habitats were concentrated in shrub forests, supporting habitat connectivity. Proximity to water bodies was critical for raptors, wading, swimming, and climbers, whereas terrestrial birds and songbirds were more affected by artificial lighting. (3) The “urban and suburban park rings” policy has effectively enhanced habitat quality and connectivity, promoting urban biodiversity resilience. This study improves our understanding of how different bird communities adapt to urbanization in terms of habitats and movement corridors, and provides useful information for formulating urban bird biodiversity conservation strategies.

Using age‐ratios to investigate the status of two Siberian Phylloscopus species in Europe

Distinguishing between vagrancy and regular migration has proved to be challenging as vagrants may, in theory, act as pioneers in the establishment of new migration routes. Because migratory songbirds tend to follow the same orientation and migration route throughout their lives, age assessment can help to distinguish individuals which have already used a route (i.e. adults) from those using it for the first time (i.e. juveniles). The presence of a significant proportion of adult individuals would suggest the presence of regular migrants in a vagrancy context. To decipher the status of two species of Siberian warblers in Europe, the Yellow‐browed Warbler Phylloscopus inornatus and the Siberian Chiffchaff P. tristis, we assessed the age‐ratios of (respectively) 324 and 117 individuals captured at different sites during the last decade. We compared whether the estimated age‐ratios differed from those estimated in Common Chiffchaff P. collybita, a common and widespread breeding and migrating species in Europe, used here as a control species. With 1.8% of birds being adult (one confirmed, five probable), the vast majority of Yellow‐browed Warblers occurring in Europe each autumn appear to be mostly, if not only, vagrants, implying that the species does not migrate regularly in Europe. These results are consistent with the very few spring records but still invite further research to unravel this remarkable phenomenon of large‐scale vagrancy. Conversely, we estimated that 9.4% and 29.7% of Siberian Chiffchaffs captured, respectively, during migration in Sweden and on regular wintering sites in southern France are adult birds, suggesting that the species could migrate towards southern Europe to winter, using a migration route in a markedly different direction from those known previously. These results urge more research to explore the origin, selection and causes of orientation variability in songbird species at the start of their first migration.

Domed nests do not offer additional environmental protection in some songbirds

Abstract Nest architecture in birds is highly variable ranging from simple scrapes through to elaborate woven constructions. In species that nest in open situations the nest can have a cup open to the elements or the nest has a dome positioned over the cup. The functional properties of domed nests have yet to be explored and this study compared the thermal insulation and rainproofing properties of nests built by four species of European songbird, two of which build domed nests whereas the others build open cup nests. Insulatory values were recorded using temperature loggers. Nests were exposed to a simulated rain event and the amount of water absorbed and the minutes for the nest to dry were determined. The nests were then deconstructed into their component parts. Materials used to build the nests differed among the species. Differences in thermal insulation were associated with the species and the size of the nest. The amount of water absorbed by a nest during a simulated rainfall event was negatively associated with the size of the nest. Feathers and moss had significant positive effects on thermal insulation and rainproofing, respectively. There was no significant difference between domed and open nests in terms of thermal insulation or rainproofing, except for the time taken for a nest to dry, which showed a significant interaction between nest mass and type of nest. Insulatory values and degree of rainproofing were like data from previous reports for songbird nests of comparable size. That no differences observed between domed and open cup nests in the species studied may reflect similarity among species, although it may be due to a paucity of data from a wider range of species building domed nests.

Ticks without borders: microbiome of immature neotropical tick species parasitizing migratory songbirds along northern Gulf of Mexico.

The long-distance, seasonal migrations of birds make them an effective ecological bridge for the movement of ticks. The introduction of exotic tick species to new geographical regions can cause the emergence of novel tick-borne pathogens. This study examined the prevalence of exotic tick species parasitizing migratory songbirds at stopover sites along the northern Gulf of Mexico using the mitochondrial 12S rRNA gene. Overall, 421 individual ticks in the genera Amblyomma, Haemaphysalis, and Ixodes were recorded from 28 songbird species, of which Amblyomma and Amblyomma longirostre were the most abundant tick genera and species, respectively. A high throughput 16S ribosomal RNA sequencing approach characterized the microbial communities and identified pathogenic microbes in all tick samples. Microbial profiles showed that Proteobacteria was the most abundant phylum. The most abundant pathogens were Rickettsia and endosymbiont Francisella, Candidatus Midichloria, and Spiroplasma. Permutation multivariate analysis of variance revealed that the relative abundance of Francisella and Rickettsia drives microbial patterns across the tick genera. We also noted a higher percentage of positive correlations in microbe-microbe interactions among members of the microbial communities. Network analysis suggested a negative correlation between a) Francisella and Rickettsia and, b) Francisella and Cutibacterium. Lastly, mapping the distributions of bird species parasitized during spring migrations highlighted geographic hotspots where migratory songbirds could disperse ticks and their pathogens at stopover sites or upon arrival to their breeding grounds, the latter showing mean dispersal distances from 421-5003 kilometers. These findings spotlight the potential role of migratory birds in the epidemiology of tick-borne pathogens.

Sperm Cryopreservation in Canaries to Protect Endangered Songbird Species: Comparison of Different Cryoprotectants.

Sperm cryopreservation is a rather complex process that needs to be adapted to wild and domestic bird species to ensure adequate efficiency. This study aimed to determine the usability of different cryoprotectants in the cryopreservation of Gloster canary sperm. For this purpose, sperm samples were collected from 12 2-year-old male Gloster canaries three times a week using cloacal massage for 4 weeks. After individual evaluation, sperm samples from the canaries were combined. Mixed sperm were divided into two groups in the study. Overall, 8% dimethyl sulfoxide (DMSO) and ethylene glycol (EG) were used as cryoprotectants. Sperm samples were drawn into straws after adding Dulbecco's Modified Eagle Medium (DMEM) extender with high glucose ratio and two different cryoprotectants in a 1:1 ratio and frozen to -80°C with liquid nitrogen vapour and then stored in liquid nitrogen at -196°C. Frozen-thawed semen samples were evaluated regarding motility, vitality, plasma membrane integrity (hypoosmotic swelling test [HOST]), density and abnormal spermatozoa rate. The highest motility value after freezing and thawing was determined in the EG group with 31.667%±4.773%. In addition, vitality, plasma membrane integrity and normal sperm morphology were statistically significantly higher in the EG-frozen group, whereas head and tail abnormality was low (p<0.05). This study determined that a DMEM extender containing 8% EG was more advantageous than a DMEM containing DMSO regarding spermatological parameters and could be used for long-term storage of canary sperm.

Pathogen priming alters host transmission potential and predictors of transmissibility in a wild songbird species.

Pathogen reinfections occur widely, but the extent to which reinfected hosts contribute to ongoing transmission is often unknown despite its implications for host-pathogen dynamics. House finches (Haemorhous mexicanus) acquire partial protection from initial exposure to the bacterial pathogen Mycoplasma gallisepticum (MG), with hosts readily reinfected with homologous or heterologous strains on short timescales. However, the extent to which reinfected hosts contribute to MG transmission has not been tested. We used three pathogen priming treatments- none, intermediate (repeated low-dose priming), or high (single high-dose priming)-to test how prior pathogen priming alters the likelihood of transmission to a cagemate during index bird reinfection with a homologous or heterologous MG strain. Relative to unprimed control hosts, the highest priming level strongly reduced maximum pathogen loads and transmission success of index birds during reinfections. Reinfections with the heterologous strain, previously shown to be more virulent and transmissible than the homologous strain used, resulted in higher pathogen loads within high-primed index birds, and showed higher overall transmission success regardless of host priming treatment. This suggests that inherent differences in strain transmissibility are maintained in primed hosts, leading to the potential for ongoing transmission during reinfections. Finally, among individuals, transmission was most likely from hosts harboring higher within-host pathogen loads, while associations between disease severity and transmission probability were dependent on a given bird's priming treatment. Overall, our results indicate that reinfections can result in ongoing transmission, particularly where reinfections result from heterologous and highly transmissible strains, with key implications for virulence evolution.

An ecological vulnerability index to assess impacts of offshore wind facilities on migratory songbirds

Abstract As offshore wind (OSW) energy expands globally, migratory songbirds are at risk of mortality from collisions with turbine blades, though the magnitude of this threat and which species are most vulnerable, remains poorly understood. Ecological vulnerability indices are commonly used to assess species' susceptibility to harmful factors, with results used to direct scarce research and monitoring resources to species showing relatively high vulnerability. These indices are based on the traits that elevate a species risk to adverse impacts (sensitivity), the overlap in occurrence between a species and the potentially harmful agent (exposure) and the influence of this exposure on the species' local or global persistence (resilience). We modified ecological vulnerability indices for seabirds to assess vulnerability of migratory songbirds to OSW related mortality. As a pertinent case study, we considered songbirds that fly across the Northwest Atlantic during their autumn migration. We utilized readily available information on each species' migratory behaviour, life history, and conservation status to calculate an index score that could range from 1 (lowest vulnerability) to 125 (highest vulnerability). We found scores of 3 to 55.2 for the 101 songbird species evaluated, with New World warblers (Parulidae) over‐represented among the highest scoring species. We found the scores to be sensitive to uncertainty in index components, highlighting the importance of considering scoring uncertainty when evaluating ecological vulnerability indices. Finally, we found that for seven of the top 10 highest scoring species, modest improvements in population trends had the potential to lower the scores substantially. Synthesis and applications. Our methodology is readily applicable to other regions where offshore wind (OSW) development is planned and songbird migration is common, allowing research and monitoring activities to be targeted to species most likely to be negatively affected by OSW facility encounters.

Phylogeography of the Red‐Headed Manakin Supports the River‐Refuge Hypothesis

ABSTRACTAimThe Amazon rainforest is one of the most biodiverse regions on earth, but our understanding of the processes that have shaped its patterns of diversity remains incomplete. One hypothesis for Amazonian speciation is the river‐refuge hypothesis, which suggests that retraction of forests away from the periphery of Amazonia, where rivers are narrow, facilitated divergence of populations separated by wide rivers. Later re‐expansion of forests would have allowed secondary contact between these populations, and co‐occurring hybrid zones may reveal the location where expanding forests first reconnected. Here, we test whether a widespread Amazonian songbird species shows evidence of population contact zones in the eastern headwaters of the Tapajós river, hypothesised to be an area of secondary contact under the river‐refuge hypothesis.LocationAmazon and Atlantic forests of South America.TaxonCeratopipra rubrocapilla (Pipridae, Passeriformes).MethodsWe sampled 147 C. rubrocapilla (Red‐headed Manakin) across its vast range, with 70 samples sequenced using reduced‐representation genomic sequencing and 139 sequenced at the mitochondrial gene cytochrome b. We use population genetic and phylogenetic analyses to investigate patterns of gene flow and population structure across the range, with a particular focus on samples from the headwaters of the Tapajós River to evaluate the potential role of the river‐refuge hypothesis.ResultsWe observe shallow population structure and evidence for widespread gene flow across the range of C. rubrocapilla. Patterns in the Tapajós headwaters match predictions of the river‐refuge hypothesis, with eastern headwater samples most similar to samples farther west on the opposite bank of the Tapajós River.Main ConclusionsThe close co‐occurrence between population contact zones within C. rubrocapilla and other previously studied hybrid zones reinforces the hypothesis that the eastern Tapajós headwaters is where rainforest populations reconnected in the past, following predictions of the river‐refuge hypothesis of Amazonian speciation.

The fecundity costs of building domed nests in birds.

Animal nests provide a beneficial environment for offspring development and as such, contribute to fitness. Gathering and transporting materials to construct nests is energetically costly, but the life history trade-offs associated with the types of nests built are largely unknown. Who contributes to building the nest could also mediate these trade-offs, as building a nest as a couple is expected to be less costly per individual than building alone. Using a comparative analysis of 227 songbird species globally, we found a fecundity cost associated with the type of nest a species builds. Species that build domed nests produce fewer broods per year than species building cups or platforms. Dome nesting species also have larger clutch sizes than open nesting species, but only when the nest is built by a couple and not when females build nests alone. This suggests that building domed nests represents a trade-off with investment in young, especially when females are solely responsible for nest building. More broadly, our results could explain macroevolutionary patterns, such as the recent finding that females, building on their own, more often build open cups rather than domed nests.

Vocal functional flexibility in a nonprimate vocal learning species

Abstract Can nonhuman animals use the same acoustic signal to transmit different illocutions on different occasions? This communicative capacity is known as vocal functional flexibility and occurs, for example, in speech, when a sentence serves different illocutionary forces or functions on different occasions based on changes to visual and intonational cues. Although common in human speech, there is a lack of clear evidence for this ability in other species. Here, we examined a likely candidate, the Brown-headed Cowbird (Molothrus ater), which is a vocal-learning songbird species that develops a repertoire of structurally distinct song types. Most of this species’ songs are directed towards conspecific males and females less than a meter away, making it unusually easy to determine the apparent target of songs, unlike the broadcast songs done by most songbirds. Songs directed to other males have clear aggressive/threatening intent, while those to females involve courtship/sexual intent. Extensive prior work shows that male cowbirds perform the visual display that accompanies singing differently in these two social settings and also modulate the intonation of song types differently. Because of these display and tonal modulations, constancy of song type usage across male- vs female-directed singing would provide evidence of vocal functional flexibility. Herein, we examined 4,828 songs in three captive flocks containing twenty-four males and thirty females during the breeding season. Males did not use their song types randomly and had strongly favored songs and less commonly used ones. Importantly, favored song types and less commonly used ones were the same whether directing courtship song to a female, aggressive song to another male or singing nonsocially with no receiver nearby. Results were consistent within and across the three flocks, providing strong evidence of vocal functional flexibility. These findings indicate that some species may evolve the ability to modulate and exaggerate visual display components and prosody more than vocal presentation per se because a learned phonological system in this and possibly other species is constrained by its vital role as an indicator trait.

Quantifying species biases among multidata sources on illegal wildlife trade and its implications for conservation.

Unsustainable wildlife consumption and illegal wildlife trade (IWT) threaten biodiversity worldwide. Although publicly accessible data sets are increasingly used to generate insights into IWT, little is known about their potential bias. We compared three typical and temporally corresponding data sets (4204 court verdicts, 926 seizure news reports, and 219 bird market surveys) on traded birds native to China and evaluated their possible species biases. Specifically, we evaluated bias and completeness of sampling for species richness, phylogeny, conservation status, spatial distribution, and life-history characteristics among the three data sets when determining patterns of illegal trade. Court verdicts contained the largest species richness. In bird market surveys and seizure news reports, phylogenetic clustering was greater than that in court verdicts, where songbird species (i.e., Passeriformes) were detected in higher proportions in market surveys. The seizure news data set contained the highest proportion of species of high conservation priority but the lowest species coverage. Across the country, all data sets consistently reported relatively high species richness in south and southwest regions, but markets revealed a northern geographic bias. The species composition in court verdicts and markets also exhibited distinct geographical patterns. There was significant ecological trait bias when we modeled whether a bird species is traded in the market. Our regression model suggested that species with small body masses, large geographical ranges, and a preference for anthropogenic habitats and those that are not nationally protected were more likely to be traded illegally. The species biases we found emphasize the need to know the constraints of each data set so that they can optimally inform strategies to combat IWT.

Feather carotenoids of the American Redstart (Setophaga ruticilla) across age and sex classes and the reliability of standard color metrics to capture pigment variation

Plumage ornaments act as important sexual signals, though the extent to which these ornaments act as honest signals—and the physiological mechanisms that maintain honesty—remain poorly understood. We studied the pigmentary basis of tail color in the American Redstart (Setophaga ruticilla), a species of songbird with sexual dichromatism and delayed plumage maturation; younger males resemble females, only replacing their yellow feathers for bright orange ones after the first breeding season. The yellow rectrices of females and young males and the orange feathers of older males largely contain the same pigments, but in vastly different proportions. Whereas the feathers of females and young males contain primarily lutein, 3′-dehydro-lutein and canary-xanthophylls, those of older males contain primarily 4-keto-carotenoids. The presence of lutein and the predominance of α-doradexanthin as 4-keto-carotenoid, a pigment with a shortened chain of conjugated double bonds compared to keto-carotenoids commonly found in red feathers, in the feathers of older males contribute to their uncommon orange hue. Since the orange coloration of the tail in the American redstart results from the combination of yellow, orange, and red pigments, this is a system where slight adjustments in the types of carotenoids deposited could significantly alter hue. Factors either work against achieving the most oxidized state in this species or the hue is maintained through stabilizing selection for a favored color. The color metrics of Carotenoid Chroma, Visible Hue, λR50 and tetrahedral θ best captured differences in pigment concentration and make-up, and are recommended in future spectrophotometric studies of carotenoid-based traits.

Pronounced early differentiation underlies zebra finch gonadal germ cell development

The diversity of germ cell developmental strategies has been well documented across many vertebrate clades. However, much of our understanding of avian primordial germ cell (PGC) specification and differentiation has derived from only one species, the chicken (Gallus gallus). Of the three major classes of birds, chickens belong to Galloanserae, representing less than 4% of species, while nearly 95% of extant bird species belong to Neoaves. This represents a significant gap in our knowledge of germ cell development across avian species, hampering efforts to adapt genome editing and reproductive technologies developed in chicken to other birds. We therefore applied single-cell RNA sequencing to investigate inter-species differences in germ cell development between chicken and zebra finch (Taeniopygia castanotis), a Neoaves songbird species and a common model of vocal learning. Analysis of early embryonic male and female gonads revealed the presence of two distinct early germ cell types in zebra finch and only one in chicken. Both germ cell types expressed zebra finch Germline Restricted Chromosome (GRC) genes, present only in songbirds among birds. One of the zebra finch germ cell types expressed the canonical PGC markers, as did chicken, but with expression differences in several signaling pathways and biological processes. The second zebra finch germ cell cluster was marked by proliferation and fate determination markers, indicating beginning of differentiation. Notably, these two zebra finch germ cell populations were present in both male and female zebra finch gonads as early as HH25. Using additional chicken developmental stages, similar germ cell heterogeneity was identified in the more developed gonads of females, but not males. Overall, our study demonstrates a substantial heterochrony in zebra finch germ cell development compared to chicken, indicating a richer diversity of avian germ cell developmental strategies than previously known.

Potential drivers of differences in breeding phenology as a component of life history strategies among coexisting species

Abstract Breeding phenology can have strong demographic consequences. Yet, the reasons why coexisting animal species differ in breeding phenology have received little attention. We tested selection pressures that underlie life history variation, such as age‐specific mortality, diet, and body size to explain breeding phenology of 16 coexisting songbird species in arid shrubland in South Africa. The average start and end dates for the earliest and latest species differed by 1.5 months, with a gradient among remaining species. Nest predation risk generally increased through the season, although species differed in seasonal patterns. Species with lower annual adult mortality, greater seasonal increases in nest predation, and greater nest predation rates had earlier start and stop dates, thereby reducing demographic risks. Species with higher adult mortality had larger brood sizes that require more food and they bred later when food was more abundant. Evolved timing of breeding thereby reflected risk management and food availability related to longevity and brood size. These factors may place unrecognized constraints on within‐species responses to climate change. Given the importance of phenology for fitness, phenology should be integrated as a core life history trait in future theory, and evolutionary constraints need to be considered in responses to climate change. Read the free Plain Language Summary for this article on the Journal blog.