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BACKGROUND: Rapid morphological change is emerging as a consequence of climate change in many systems. It is intuitive to hypothesize that temporal morphological trends are driven by the same selective pressures that have established well-known ecogeographic patterns over spatial environmental gradients (e.g., Bergmans and Allens rules). However, mechanistic understanding of contemporary morphological shifts is lacking. RESULTS: We combine morphological data and whole genome sequencing from a four-decade dataset in the migratory bird hermit thrush (Catharus guttatus) to test whether morphological shifts over time are accompanied by genetic change. Using genome-wide association, we identify alleles associated with body size, bill length, and wing length. Shifts in morphology and concordant shifts in morphology-associated alleles over time would support a genetic basis for the observed changes in morphology over recent decades, potentially an adaptive response to climate change. In our data, bill size decreases were paralleled by genetic shifts in bill size-associated alleles. On the other hand, alleles associated with body size showed no shift in frequency over time. CONCLUSIONS: Together, our results show mixed support for evolutionary explanations of morphological response to climate change. Temporal shifts in alleles associated with bill size support the hypothesis that selection is driving temporal morphological trends. The lack of evidence for genetic shifts in body size alleles could be explained by a large role of plasticity or technical limitations associated with the likely polygenic architecture of body size, or both. Disentangling the mechanisms responsible for observed morphological response to changing environments will be vital for predicting future organismal and population responses to climate change.

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

How do chemically defended animals resist their own toxins? This intriguing question on the concept of autotoxicity is at the heart of how species interactions evolve. In this issue of Molecular Ecology (Molecular Ecology, 2024, 33), Bodawatta and colleagues report on how Papua New Guinean birds coopted deadly neurotoxins to create lethal mantles that protect against predators and parasites. Combining chemical screening of the plumage of a diverse collection of passerine birds with genome sequencing, the researchers unlocked a deeper understanding of how some birds sequester deadly batrachotoxin (BTX) from their food without poisoning themselves. They identified that birds impervious to BTX bear amino acid substitutions in the toxin-binding site of the voltage-gated sodium channel Nav1.4, whose function is essential for proper contraction and relaxation of vertebrate muscles. Comparative genetic and molecular docking analyses show that several of the substitutions associated with insensitivity to BTX may have become prevalent among toxic birds through positive selection. Intriguingly, poison dart frogs that also co-opted BTX in their lethal mantles were found to harbour similar toxin insensitivity substitutions in their Nav1.4 channels. Taken together, this sets up a powerful model system for studying the mechanisms behind convergent molecular evolution and how it may drive biological diversity.

The process of decision making is a complex procedure influenced by both external and internal conditions. Songbirds provide an excellent model to investigate the neural mechanisms of decision making, because females rely on acoustic signals called songs as important stimuli in directing their mate choice. Previous experiments by our group and others have implicated secondary auditory brain sites in female evaluation of song quality, including the caudal portions of the nidopallium (NC) and mesopallium (CM). Recent pathway tracing experiments reveal a convergence of those sites onto a third region, the ventral portion of the intermediate arcopallium (AIV), suggesting that AIV may also play an important role in song evaluation and mate choice. Here we combined behavioral testing with lesion inactivation to investigate the role of AIV in song preference of female Bengalese finches (Lonchura striata domestica). Inactivation of AIV was associated with destabilization of rank ordering of song preferences. These data suggest a model in which the convergence of auditory activity in AIV plays an important role in female perception of song quality and production of courtship behaviors. Together with previous results that also demonstrate a role for the auditory areas that converge onto AIV, these findings extend the experimental tractability of this emerging animal model of sensory perception and decision making. [ABSTRACT FROM AUTHOR]

The accurate and reliable performance of learned vocalizations (e.g., speech and birdsong) modulates the efficacy of communication in humans and songbirds. Consequently, it is critical to understand the factors that regulate the performance of learned vocalizations. Across taxa, neural circuits underlying motor learning and control are replete with perineuronal nets (PNNs), and we analyzed how PNNs in vocal motor circuitry regulate the performance of learned song in zebra finches. We report that developmental increases in PNN expression in vocal circuitry are associated with developmental increases in song stereotypy. We also document that enzymatically degrading PNNs in the motor nucleus HVC acutely altered song structure (changes in syllable sequencing and production). Collectively, our data reveal a causal contribution of PNNs to the performance of learned behaviors and, given the parallels in the regulation of birdsong and speech, suggest that PNNs in motor circuitry could modulate speech performance. Manipulating perineuronal nets (PNNs) in the motor nucleus HVC of zebra finches alters the structure of vocalizations acquired during development, highlighting a causal contribution of PNNs in motor circuitry to the performance of learned behaviors. [ABSTRACT FROM AUTHOR]

Simple Summary: Colourful animals are often more conspicuous than dull animals, which increases their exposure to predators. One way to reduce predation risk could be to be more vigilant. We investigated this in two related songbird species, the colourful Gouldian finch and the less colourful long-tailed finch, at waterholes by measuring the frequency of head movements as a measure of vigilance. Both species showed a high frequency of head movements (high vigilance) when sitting in an open tree where they could be easily spotted. However, the more conspicuous Gouldian finch remained more vigilant when sitting under cover than the long-tailed finch. Moreover, juveniles and adults of the Gouldian finch had similar vigilance levels; whereas, juvenile long-tailed finches were less vigilant than their adult counterparts, possibly because of the juveniles often being in family groups. Both species showed a similar reduction in vigilance shortly after landing in the tree. The reduction in vigilance was affected by group size. This indicates initial uncertainty about the threat they might face, more so when alone. Finally, vigilance was higher at small waterholes, reflecting a higher perceived risk, as compared to larger waterholes. 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. [ABSTRACT FROM AUTHOR]

Despite the wide use of zebra finches as an animal model to study vocal learning and production, little is known about impacts on their welfare caused by routine experimental manipulations such as changing their social context. Here we conduct a post-hoc analysis of singing rate, an indicator of positive welfare, to gain insights into stress caused by social isolation, a common experimental manipulation. We find that isolation in an unfamiliar environment reduces singing rate for several days, indicating the presence of an acute stressor. However, we find no such decrease when social isolation is caused by either removal of a social companion or by transfer to a familiar environment. Furthermore, during repeated brief periods of isolation, singing rate remains high when isolation is induced by removal of social companions, but it fails to recover from a suppressed state when isolation is induced by recurrent transfer to an unknown environment. These findings suggest that stress from social isolation is negligible compared to stress caused by environmental changes and that frequent short visits of an unfamiliar environment are detrimental rather than beneficial. Together, these insights can serve to refine experimental studies and design paradigms maximizing the birds' wellbeing and vocal output. [ABSTRACT FROM AUTHOR]

The arid belt of Central Asia constitutes a barrier for small landbirds during autumn migration. Some species that migrate from Siberia to Africa circumvent this barrier by taking a detour around the northern coast of the Caspian Sea. It becomes increasingly clear that at least some songbirds that migrate between eastern Europe and southern Asia also perform a detour along the northern edge of the desert. Trapping data from the northern fringe of the barrier collected in this study (Orenburg Region of Russia, 51° 22′ N, 61° 23′ E; September 2023) and from earlier studies performed west and east of our study site show that some songbirds that migrate from European breeding grounds towards south and south-eastern Asian wintering quarters make a direct crossing, whereas others make a detour and circumvent Central Asian deserts. Ecological differences between the species of migrants cannot explain the observed pattern. Those species that make a detour are the ones that are considered to have colonized Europe from their ancestral breeding areas east of the Ural Mountains most lastly. [ABSTRACT FROM AUTHOR]

Song divergence driven by social learning has been proposed to be a key factor driving allopatric speciation in oscine birds. Songbirds often respond more to songs deriving from their local population, suggesting the potential for acoustic divergence across populations to shape both intra- and intersexual interactions. However, many of these studies were conducted on species with simple songs and, as a result, we know comparatively little about the emergence of population differences and song discrimination in species with complex songs. We addressed this question in the pied flycatcher (Ficedula hypoleuca) by calculating the dissimilarity of songs from 2 foreign populations as well as from our study site to the local centroid. We then conducted a paired-design playback experiment where both local and foreign songs were played simultaneously. We found that pied flycatcher males showed significantly stronger responses to those songs that sounded more similar to the local population. This suggests that despite the high complexity of the pied flycatcher song, individuals are still able to discriminate across populations. Our results support the hypothesis that learned song divergence can act as a mechanism for assortative mating and allopatric speciation. [ABSTRACT FROM AUTHOR]

Aim: The 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. Location: Amazon and Atlantic forests of South America. Taxon: Ceratopipra rubrocapilla (Pipridae, Passeriformes). Methods: We 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. Results: We 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 Conclusions: The 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. [ABSTRACT FROM AUTHOR]

Beak morphology in birds is often linked to diet. In this study, we aimed to analyse whether diet or other drivers, such as allometry or species relatedness, explain the morphological beak variation of Neotropical passerines and whether there are specific predictors for beak shape variation for the two passerine suborders, Oscines and Suboscines. We analysed beak measurements (length, width, and depth) as response variables and body size, diet, and phylogenetic distance as predictor variables. After controlling for allometry which had major impact on beack shape, beak length and depth exhibited significant differences across diet categories and between suborders. Compared with Oscines, the beak shape of Suboscines is more influenced by species relatedness, probably owing to niche conservatism. Our findings suggest an adaptive convergence between the two passerine suborders in the Neotropics, driven mainly by allometric constraints rather than by the trophic niche. [ABSTRACT FROM AUTHOR]

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The article discusses the use and definitions of the terms "arena," "lek," and "court" in describing avian courtship sites. It argues that "arena" is inaccurate and inappropriate, while "lek" is the more appropriate term. The author reviews historical and contemporary literature to clarify the distinctions between these terms and emphasizes the importance of using accurate terminology in ornithology. The article provides definitions for "lek," "dispersed lek," "lekking," and "court," aiming to eliminate confusion and promote clarity in describing avian courtship behavior. [Extracted from the article]

Vegetation structural complexity surrounding nests can either provide concealment for intruders and mates or make it more difficult for hosts to recognize parasitic eggs. We investigated whether shading and vegetation aggregation increase extrapair paternity (the presence of broods with half‐siblings) and intraspecific brood parasitism (IBP, the occurrence of broods with unrelated offspring) in socially monogamous Blue‐black Grassquits Volatinia jacarina. We found that habitat shadowing was associated with increased occurrence of IBP, but found no association between the degree of shade and the presence of extrapair offspring. Our findings support the idea that habitat limits cryptic reproductive behaviours and that female grassquits may benefit from habitat shadows to parasitize conspecific nests. [ABSTRACT FROM AUTHOR]

Vocalizations are one of the key premating reproductive barriers that could affect species formation. In song-learning birds, vocal traits are sometimes overlooked in species delimitation, as compared to morphological or plumage-based differences. In this study, we assessed geographic variation in songs of eight pairs of oscines on two scales: (1) comparing primary songs of species/subspecies pairs whose breeding grounds are eastern and western counterparts of each other in the continental North America, and (2) for each counterpart, identifying and comparing possible variation among their populations. We found that there were strong differences in the songs between eastern and western taxa, though the magnitude of that difference was not correlated to a mitochondrial DNA-based estimates of divergence. Additionally, we found that within-taxa geographic variation was not common in our focal taxa, beyond a single species (Townsend's warbler, Setophaga townsendi). The result of this study provides a standardized, quantitative comparison of eastern and western songbirds, and serves as the foundation to explore the possible effectiveness of vocalizations as a reproductive barrier at this geographic scale. [ABSTRACT FROM AUTHOR]

Background: Understanding the neural basis of behavior requires insight into how different brain systems coordinate with each other. Existing connectomes for various species have highlighted brain systems essential to various aspects of behavior, yet their application to complex learned behaviors remains limited. Research on vocal learning in songbirds has extensively focused on the vocal control network, though recent work implicates a variety of circuits in contributing to important aspects of vocal behavior. Thus, a more comprehensive understanding of brain-wide connectivity is essential to further assess the totality of circuitry underlying this complex learned behavior. Results: We present the Oscine Structural Connectome for Investigating NEural NETwork ORGanization (OSCINE-NET.ORG), the first interactive mesoscale connectome for any vocal learner. This comprehensive digital map includes all known connectivity data, covering major brain superstructures and functional networks. Our analysis reveals that the songbird brain exhibits small-world properties, with highly connected communities functionally designated as motor, visual, associative, vocal, social, and auditory. Moreover, there is a small set of significant connections across these communities, including from social and auditory sub-communities to vocal sub-communities, which highlight ethologically relevant facets of vocal learning and production. Notably, the vocal community contains the majority of the canonical vocal control network, as well as a variety of other nodes that are highly interconnected with it, meriting further evaluation for their inclusion in this network. A subset of nodes forms a "rich broker club," highly connected across the brain and forming a small circuit amongst themselves, indicating they may play a key role in information transfer broadly. Collectively, their bidirectional connectivity with multiple communities indicates they may act as liaisons across multiple functional circuits for a variety of complex behaviors. Conclusions: OSCINE-NET.ORG offers unprecedented access to detailed songbird connectivity data, promoting insight into the neural circuits underlying complex behaviors. This data emphasizes the importance of brain-wide integration in vocal learning, facilitating a potential reevaluation of the canonical vocal control network. Furthermore, we computationally identify a small, previously unidentified circuit—one which may play an impactful role in brain-wide coordination of multiple complex behaviors. [ABSTRACT FROM AUTHOR]

Zebra finches undergo a gradual refinement of their vocalizations, transitioning from variable juvenile songs to the stereotyped song of adulthood. To investigate the neural mechanisms underlying song crystallization—a critical phase in this developmental process—we performed intracellular recordings in HVC (a premotor nucleus essential for song learning and production) of juvenile birds. We then compared these recordings to previously published electrophysiological data from adult birds. We found that HVC projection neurons in juvenile zebra finches during the song crystallization phase exhibited more variable spiking patterns compared to the precise bursting observed in adult HVC projection neurons. Additionally, subthreshold membrane potential fluctuations in juvenile neurons exhibited longer durations and larger amplitude excitatory postsynaptic potentials. These distinct temporal dynamics in HVC during song crystallization likely play a crucial role in the fine-tuning processes that shape the precise timing and structure of the mature zebra finch song. [ABSTRACT FROM AUTHOR]

Singing is known to play significant roles in songbird communication. For a long time, singing was believed to be a male attribute, whereas rare episodes of female singing were seen as deviations. However, there has been more and more research on female vocals in recent times, suggesting this in no way to be a rare event. In this study, we investigated the vocalization of the black-hooded oriole (Oriolus xanthornus) in Nam Cat Tien National Park, southern Vietnam. We identified two singing variants significantly differing in both maximum frequency and frequency range, these parameters being higher in variant 2. Variant 1 appeared to be more often, being performed in various situations: spontaneous singing, territorial interactions, and duets. Variant 2 occurred only in duets or in territorial interactions where the bird focal pair also performed in duets. No syntax variation was found between the different singing variants. In addition, no variation was revealed in the syntax of variant 1 in the different situations (spontaneous singing and duets). In one observation, we reliably discovered that the male used variant 1, while the female used variant 2. Variant 1 is likely usually to be used by males, while variant 2 is typically used by females. We also identified two types of calls for this species. [ABSTRACT FROM AUTHOR]

A brief historical review is presented of the development of approaches to the study of the territorial space of songbirds (Oscines), using both older and current research methods. The study of bird territoriality has continued for more than a century, but there are still not only little-known aspects that remain in this direction, but also no consensus on terminology and methods. The description of the territorial space plays leading roles in such works. In turn, the classic objects of such research are songbirds demonstrating their territories by singing and defending them from invasion by other individuals. There have been many definitions proposed for the term "territory," which reflect different concepts of territoriality. The most common definition of a territory thereby is a defended (conceptually) and demonstrated (operationally) space. As a rule, this space is a certain area, a projection of the real territory to the surface on the ground. In recent decades, however, publications have appeared on the topic of exploring territories as three-dimensional (3D) structures. The most effective method of field registration of territories remains the territory mapping method based on visual observations of tagged individuals, which has also been adapted for 3D-territories. Alternative approaches to the registration of territories, including radio telemetry, have significant limitations. In terms of quantitative data-processing methods, there has been a shift over the past decades from an analysis of territories as polygons to their analysis as kernel isopleths. This approach allows for not only the territory contours to be understood, but also the frequency of the use of different points within its limits to be assessed. A significant achievement in recent years is the adaptation of the kernel methods to three-dimensional structures. It can be said that there is a need to study the territoriality of birds in the 3D-environment. Such research seems very promising because it can provide fundamentally new information on topics such as habitat selection and space use, the formation of the spatial and ethological structure of settlements, the separation of territories under high population densities and limited resources, and both intra- and interspecific competition. [ABSTRACT FROM AUTHOR]

ABSTRACT Our understanding of elaborate signaling behaviors, such as bird song, has been hindered by historical biases towards male animals. Bird song has been shown to serve important functions like defending territories or attracting mates in both males and females, and singing in both sexes is likely the ancestral trait for songbirds. Female song is strongly associated with year‐round territory defense, especially in the tropics. However, more studies of both male and female songs are needed to better understand the selection pressures acting on this elaborate signal trait. The common ancestor of the New World orioles (Icterus) was likely a nonmigratory tropical species, with both males and females singing and defending year‐round territories. The Puerto Rican Oriole (Icterus portoricensis) has these natural history characteristics, but little is known about how each sex uses song in this understudied Caribbean endemic. We found that while male and female songs were significantly different acoustically, they were indistinguishable in the field, and showed no sex‐specific pattern in syllable usage. Males sang at higher rates than females during the dawn chorus, but females sang frequently during the day. Song is likely evolving as a unified trait in this species, reflecting the characteristics of the common ancestor, but may serve different functions for each sex. In the future, playback studies and rate observations throughout the full day and throughout the year will provide additional insight into how males and females of this tropical songbird may be using their songs. [ABSTRACT FROM AUTHOR]

Animal populations can exhibit dramatic variation in individual fitness, and microbiota are emerging as a potentially understudied factor influencing host health. Bacterial diversity and community structure of the gut microbiome are associated with many aspects of fitness in animals, but relatively little is known about the generality of these relationships in wild populations and non‐mammalian taxa. We studied the northern cardinal Cardinalis cardinalis, a member of a taxon that is ecologically important but underrepresented in microbiome research: songbirds. To test for relationships between the microbiota and host fitness, we sampled the cloacal microbiomes of wild cardinals and measured body condition index, assessed coloration of sexual ornaments (beak and plumage), and collected blood to estimate the glucocorticoid response to stress. Both alpha and beta bacterial diversity were related to individual variation in body condition and several sexual ornaments, but not glucocorticoid concentrations. Our results from a free‐living songbird population add to a growing body of research linking avian host fitness to internal bacterial community characteristics. This study sets the stage for manipulative experiments to determine how challenges to fitness and microbiomes may upset these relationships. [ABSTRACT FROM AUTHOR]

Arctic‐breeding birds exhibit around‐the‐clock activity, and these activity cycles are postulated to maximize reproductive success during the short breeding season characteristic of high‐latitude regions. Two closely related species of arctic‐breeding songbirds, Lapland longspurs (Calcarius lapponicus; ground‐nesting) and snow buntings (Plectrophenax nivalis; cavity‐nesting) exhibit extended activity cycles throughout the polar day (71° N) except for 4–5 h of daily quiescence. Ground‐nesting Lapland longspurs experience higher levels of nest predation than cavity‐nesting snow buntings, and this difference is reflected in elevated nest vigilance in male longspurs compared with snow buntings. In this study, we examined the effect of melatonin supplementation upon male parental care, corresponding measures of nestling growth, and ability to reduce activity (and increase sleep). A pharmacological dose of melatonin in captive snow buntings dampened the amplitude of activity rhythms over the polar day with no detectable phase‐shifting compared with control‐implanted birds. Melatonin treatment reduced nest visits and overall time spent on the nest by male snow buntings compared with controls. There was no significant increase in time spent by female snow buntings on the nest to compensate for this, and there was no significant effect on offspring growth rates. There were no effects of melatonin supplementation on longspur adults or offspring, suggesting behavioral insensitivity to exogenous melatonin treatment. These differences in sensitivity underscore the importance of nest defense in ground‐nesting longspurs compared with cavity‐nesting snow buntings, which participate minimally in nest defense. Research Highlights: Melatonin supplementation altered male parental care in a cavity‐nesting arctic‐breeding bird, the snow bunting (Plectrophenax nivalis).Melatonin supplementation dampened activity rhythms.Lapland longspurs (Calcarius lapponicus), a ground‐nesting congener, were unaffected by melatonin treatment. [ABSTRACT FROM AUTHOR]

Seasonal changes in sleep/wake cycles and behaviors related to reproduction often co‐occur with seasonal fluctuations in sex hormones. Experimental studies have established that fluctuations in circulating testosterone mediate circadian rhythms. However, most studies are performed under constant lighting conditions and fail to investigate the effects of testosterone on the phenotypic output of circadian rhythms, that is, chronotype (daily activity patterns under light:dark cycles). Here, we experimentally elevated testosterone with implants during short nonbreeding daylengths in male house sparrows (Passer domesticus) to test if observed seasonal changes in chronotype are directly in response to photoperiod or to testosterone. We fitted individuals with accelerometers to track activity across treatment periods. Birds experienced three treatments periods: short day photoperiods before manipulation (SD), followed by testosterone implants while still on short days (SD + T). Implants were then removed. After a decrease in cloacal protuberance size, an indicator of low testosterone levels, birds were then photostimulated on long days (LD). Blood samples were collected at night, when testosterone peaks, to compare testosterone levels to daily onset/offset activity for experimental periods. Our results indicate that experimentally elevated testosterone under short nonbreeding photoperiods significantly advanced daily onset of activity and total daily activity relative to daylength. This suggests that testosterone, independent of photoperiod, is responsible for seasonal shifts in chronotypes and daily activity rhythms. These findings suggest that sex steroid hormone actions regulate timing of daily behaviors, likely coordinating expression of reproductive behaviors to appropriate times of the day. Summary: Experimentally elevated testosterone advanced onset of daily activity and increased total activity during the photophase during short days.Photostimulation delayed daily onset activity and reduced total activity during the photo‐phase. [ABSTRACT FROM AUTHOR]

Animal vocalisations are widely used to signal strength or motivation of a caller in competitive interactions, such as in territorial defence. Substantial understanding of signalling functions in territorial conflicts is based on singing by male songbirds. Yet, in many species, both pair members call during territorial conflicts, as well as in predator‐induced situations, leading to complex signalling interactions in which calls overlap or alternate. This raises the question as to whether or not variation in how individuals in pairs time their calls is perceived as meaningful by receivers. Here, we tested with playback experiments whether Eurasian magpies (Pica pica), a species producing alarm calls (so‐called chatter calls) in territorial defence, respond stronger to simulated pair‐intruders who overlap their calls with each other than to those who alternate them. Magpies emitted a significantly longer first chatter calls in response to playback with overlapping calls but chattered significantly sooner and approached the loudspeakers significantly more closely in response to playbacks of alternating (and therefore longer) call sequences. These findings exemplify that the timing of calls by pair members matters, but in more complex ways than we predicted. The overlapping playback appeared to trigger a longer yet later initial chatter response and a weaker approach response, suggesting that the different ways in which magpies respond reflect different levels of arousal or defence strategies. The results may also reflect uncertainty by receivers due to a potential mismatch between signalled and perceived information: While overlapping calls may signal high arousal by both callers, a longer alternating sequence could be perceived as a more aroused longer signal. These findings expand on classical experiments on call function, suggesting that pairs can vary the message by coordinating their alarm calls in different ways, similar to how duetting pairs time their song contributions in advertisement signalling. [ABSTRACT FROM AUTHOR]

Temperate winters can impose severe conditions on songbirds that threaten survival, including shorter days and often lower temperatures and food availability. One well-studied mechanism by which songbirds cope with such conditions is seasonal acclimatization of thermal metabolic traits, with strong evidence for both preparative and responsive changes in thermogenic capacity (i.e. the ability to generate heat) to low winter temperatures. However, a bird's ability to cope with seasonal extremes or unpredictable events is likely dependent on a combination of behavioral and physiological traits that function to maintain allostatic balance. The ability to cope with reduced food availability may be an important component of organismal response to temperate winters in songbirds. Here, we compare responses to experimentally reduced food availability at different times of year in captive red crossbills (Loxia curvirostra) and pine siskins (Spinus pinus)—two species that cope with variable food resources and live in cold places—to investigate seasonal changes in the organismal response to food availability. Further, red crossbills are known to use social information to improve responses to reduced food availability, so we also examine whether the use of social information in this context varies seasonally in this species. We find that pine siskins and red crossbills lose less body mass during time-restricted feedings in late winter compared to summer, and that red crossbills further benefit from social information gathered from observing other food-restricted red crossbills in both seasons. Observed changes in body mass were only partially explained by seasonal differences in food intake. Our results demonstrate seasonal acclimation to food stress and social information use across seasons in a controlled captive environment and highlight the importance of considering diverse physiological systems (e.g. thermogenic, metabolic, digestive, etc.) to understand organismal responses to environmental challenges. [ABSTRACT FROM AUTHOR]

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

Vocal rhythm plays a fundamental role in sexual selection and species recognition in birds, but little is known of its genetic basis due to the confounding effect of vocal learning in model systems. Uncovering its genetic basis could facilitate identifying genes potentially important in speciation. Here we investigate the genomic underpinnings of rhythm in vocal non-learning Pogoniulus tinkerbirds using 135 individual whole genomes distributed across a southern African hybrid zone. We find rhythm speed is associated with two genes that are also known to affect human speech, Neurexin-1 and Coenzyme Q8A. Models leveraging ancestry reveal these candidate loci also impact rhythmic stability, a trait linked with motor performance which is an indicator of quality. Character displacement in rhythmic stability suggests possible reinforcement against hybridization, supported by evidence of asymmetric assortative mating in the species producing faster, more stable rhythms. Because rhythm is omnipresent in animal communication, candidate genes identified here may shape vocal rhythm across birds and other vertebrates.

Recent studies have shown that nocturnal singing in diurnal birds is a common phenomenon, however, the understanding of the mechanisms, functions and consequences of this behaviour has been lacking. We focused on the night singing of two diurnal songbirds–the yellowhammer and the common chaffinch that are widely distributed in Europe. We conducted day and night playback experiments, during which we broadcast songs of an unfamiliar male to the territory holder at two different stages of the breeding season, to examine whether the night singing in species which normally do not sing at night elicits responses from their conspecifics. We hypothesized that if nocturnal singing had no function, birds would ignore the night-time playback and respond only to the daytime intrusion. Otherwise, a response to the night-time playback would suggest that night singing may increase reproductive success but is limited by ecological factors. We found that, in contrast to the diurnal experiment, neither species responded vocally to the nocturnal playback. In yellowhammers, the probability of flights was higher during and after the playback than before it. This pattern was similar both during the day and night and did not differ between the stages of the season. For the common chaffinches, the probability of flight was low at night and constant across treatments, in contrast to the day when we observed more flights during the playback stage than before and after it. The playback of either species' songs at night caused the approach of predators, which was not observed during the day. The observed discrepancy in the probability of flights between the species suggests that nocturnal singing is a functional trait that affects other individuals in a specific context. Nocturnal singing does not seem to be a simple behaviour that extends during the day; it is a complex mechanism potentially dependent on specific conditions related to intraspecific communication, predatory pressure, local female access, or species' evolutionary history. We emphasise that those ecological and evolutionary factors need to be taken into account to understand this phenomenon widely. [ABSTRACT FROM AUTHOR]

During courtship, animals perform conspicuous and elaborate signals. In birds, courtship involved often mutual engagement by both partners but most research on courtship behaviours has focused on male signals despite of growing interest for female signals in recent years. Here, we show that female domestic canaries (Serinus canaria) have the ability to modulate their sexual response to male songs. To do so, we exposed females to two types of song (very attractive and moderately attractive songs) during two consecutive reproductive cycles. We measured both visual (copulation solicitation displays, CSD) and vocal signals (copulation solicitation trills, CST; contact calls, CC and simple trills, ST) emitted by the females during song broadcast. We observed that females could modify the characteristics of their signals (duration and the number of elements of CSD, duration, frequency and number of notes of calls) depending on song attractiveness and the number of times they were exposed to a male's song. We also found that some females always emitted more signals than others (i.e. stable inter‐individual differences) regardless of the song attractiveness and across reproductive cycles. Further studies are necessary to check whether female signals constitute sexual ornaments and if they could stimulate male canaries during courtship. [ABSTRACT FROM AUTHOR]

Many building blocks of human language can be found within the vocal communication systems of other species, most notably songbirds. One of the most prominent of these building blocks is syntax. While studies of syntax are abundant, a lack of consensus on the definition of syntax in non‐human animal communication studies has led to much debate. Consistent and deliberate use of terminology is needed to facilitate understanding across disciplines. In addition, new terminology may better describe syntactic structure found in vocal signals that are devoid of semantic associations, such as birdsong. Here, we propose two terms to describe the types of syntax commonly found in birdsong: sequential syntax and dialectical syntax. Sequential syntax can be defined as the rules that govern the patterns of sound without regard to semantic meaning. Dialectic syntax can be defined as sequential syntax that is distinct among different populations or groups with behavioral significance for those groups. Taken together, these two terms can describe the type of syntax seen in ornamental signals, such as birdsong. [ABSTRACT FROM AUTHOR]

For territorial animals, the behavior of conspecific neighbors sets the social context of communication. Despite numerous investigations of vocalizations related to territory defense and mate attraction, the effect of neighbor density on animal vocal behavior has received little attention, particularly in tropical animals and animals where both sexes produce complex acoustic signals. In this study, we used an innovative multispeaker playback experiment to manipulate the apparent density of neighbors in rufous-and-white wrens, Thryophilus rufalbus , living in Costa Rica's tropical dry forest. In this tropical songbird, both males and females defend year-round territories and sing complex, learned songs for territory defense. We recorded the singing behavior of 24 subjects (12 pairs), and then we used an array of 6 loudspeakers to simulate the presence of 6 new territorial neighbors (3 simulated pairs) outside each subject pair's breeding territory. The stimuli persisted for 3 consecutive days, with both male and female songs broadcast at a natural rate from dawn to dusk. We found that the mean male song rate increased by almost 50% in response to the simulated increase in local density. Females showed less frequent song-type switching rates following the simulated increase in local density, although it was a marginal increase. These findings reveal that male and female songbirds' vocal behavior varies with the local density of territorial neighbors. We conclude that birds are sensitive to acoustic signals of conspecific density arising from sounds beyond their territory boundaries, and that they use this public information to guide their vocal behavior. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

Nest construction is a feature of a range of taxa, yet the functional properties of nests are poorly understood. Avian nests offer thermal insulation, structural support and protection from rain, but to date there are few studies that have explored these functions for mammal nests. Here nests constructed by harvest mice (Micromys minutus) were studied ex situ to determine the thermal insulation provided by the nest wall and the degree to which simulated rainfall was absorbed. Nests were collected from across Great Britain and analysis explored whether nest size and geographical location affected insulation or rainproofing. Nests were constructed from grass leaves woven into an outer wall that surrounded smaller pieces of grass that filled the interior of the nest. Nest mass was positively related to thermal insulation but unrelated to geographical location. By contrast, nest mass was positively related to the amount of water nest absorbed after simulated rain but volume and longitude were inversely related to the time it took the nest to dry out. In many ways, harvest mice nests had similar functional properties to those of small songbirds, i.e., to provide thermal insulation and rainproofing. This study was the first to explore the environmental protection potentially offered to harvest mice by their nests. The study has highlighted our poor understanding of the factors that determine the function of mammal nests. There is scope for more research into the functional properties, e.g., thermal insulation or rainproofing, of a wide variety of mammal nests. [ABSTRACT FROM AUTHOR]

Germline de novo mutations (DNMs) provide the raw material for evolution. The DNM rate varies considerably between species, sexes and chromosomes. Here, we identify DNMs in the zebra finch (Taeniopygia guttata) across 16 parent-offspring trios using two genome assemblies of different quality. Using an independent genotyping assay, we validate 82% of the 150 candidate DNMs. DNM rates are consistent between both assemblies, with estimates of 6.14 × 10–9 and 6.36 × 10–9 per site per generation. We observe a strong paternal bias in DNM rates (male-to-female ratio ɑ ≈ 4), but this bias is in transition mutations only, leading to a transition-to-transversion ratio of 3.18 and 3.57. Finally, we find that DNMs tend to be randomly distributed across chromosomes, not associated with recombination hotspots or genic regions. However, the sex chromosome chrZ shows a roughly fourfold increased DNM rate compared to autosomes, which is more than the expected increase due to chrZ spending two-thirds of its time in males. Overall, our results further enhance our understanding of DNMs in passerine songbirds. Germline de novo mutations (DNMs) in zebra finches were identified across 16 trios, with an estimated DNM rate of 6 × 10−9 per site per generation. A paternal bias in transition mutations was observed, with a higher DNM rate on the sex chromosome Z. [ABSTRACT FROM AUTHOR]

Bird song contains crucial information that enables recognition of conspecific individuals from a distance, which facilitates subsequent complex behaviors related to mate attraction and rival deterrence. Loud broadcast signals of non‐learning bird species are usually treated as less complex than songs of Oscines, but several studies have revealed that song learning is not necessary for the evolution of complex signaling. Here, we focused on a species of African wood‐dove which produces superficially simple songs consisting of short notes organized into two parts of different amplitude. Our model was a population of emerald‐spotted wood‐doves (Turtur chalcospilos) that live in the same area as the physically and vocally similar blue‐spotted wood‐dove (Turtur afer). We tested the responses of male emerald‐spotted wood‐doves to different playbacks simulating territorial intrusion. We used songs of the focal species and of the congener, two types of artificially mixed songs with different parts belonging to the focal or congeneric species, and a control song. We aimed to assess (i) whether the focal species responds only to its own species' song or exhibits interspecific territoriality, and (ii) which part of the song is responsible for coding species identity. We found that male emerald‐spotted wood‐doves responded strongly to playback, but almost exclusively approached only the playback of their own species' song. Additionally, only conspecific song caused a decrease in song rate during playback and an increase in song output after playback. Our results suggest that emerald‐spotted wood‐doves are able to discriminate their own songs from those of congeners and do not exhibit interspecies territoriality. We were unable to identify a single part of the song that codes species‐specificity, as mixed songs of any kind did not substantially increase responsiveness to playback in comparison to the congener song or the control. We discuss these results in the context of current hypotheses regarding interspecific territoriality and the evolution of species‐identity coding. [ABSTRACT FROM AUTHOR]

Life history theory predicts increased parental investment comes with fitness costs, often expressed as negative effects on survival and future reproduction. To better understand the costs of reproduction and life history trade‐offs, we evaluated calcium supplementation at a high‐elevation site in Colorado as a novel approach to experimentally alter reproductive investment in nesting female Tachycineta bicolor (tree swallow). Calcium is a nutrient critical to avian reproduction as the intake of natural calcium is essential for egg production, embryo development, and nestling growth. Altering calcium availability exclusively during the breeding season allowed examination of individual biological responses to experimental modification of reproduction, as well as the reproductive costs associated with egg production and laying an entire clutch. As a functional endpoint and proxy for fitness and longevity, telomere length was measured at the beginning and end of each breeding season. Telomeres—protective "caps" at the ends of chromosomes—have been shown to shorten with aging and a variety of stressors, including higher reproductive output. Results demonstrate that tree swallow mothers supplemented with calcium during the breeding season experience higher reproductive output and produce offspring with longer telomeres, which came at the cost of relatively shorter telomeres during the reproductive season. These findings provide additional support for reproductive trade‐offs, and also challenge previous calcium supplementation studies that suggest excess calcium reduces the cost of reproduction. [ABSTRACT FROM AUTHOR]

The process of reproductive character displacement involves divergence and/or the narrowing of variance in traits involved in species recognition, driven by interactions between taxa. However, stabilizing sexual selection may favor stasis and species similarity in these same traits if signals are optimized for transmission through the prevailing environment. Further, sexual selection may promote increased variability within species to facilitate individual recognition. Here we ask how the conflicting selection pressures of species recognition and sexual selection are resolved in a genus of Himalayan birds that sing exceptionally similar songs. We experimentally show that small differences in two traits (note shape and peak frequency) are both necessary and sufficient for species recognition. Song frequency shows remarkable clinal variation along the Himalayan elevational gradient, being most divergent where species co-occur, the classic signature of reproductive character displacement. Note shape shows no such clinal variation but varies more between individuals of an allopatric species than it does among individuals within species that co-occur. We argue that the different note shapes experience similar transmission constraints, and differences produced through species interactions spread back through the entire species range. Our results imply that reproductive character displacement is likely to be common. [ABSTRACT FROM AUTHOR]

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

Birds play a pivotal role in ecosystem and biodiversity research, and accurate bird identification contributes to the monitoring of biodiversity, understanding of ecosystem functionality, and development of effective conservation strategies. Current methods for bird sound recognition often involve processing bird songs into various acoustic features or fusion features for identification, which can result in information loss and complicate the recognition process. At the same time, the recognition method based on raw bird audio has not received widespread attention. Therefore, this study proposes a bird sound recognition method that utilizes multiple one-dimensional convolutional neural networks to directly learn feature representations from raw audio data, simplifying the feature extraction process. We also apply positional embedding convolution and multiple Transformer modules to enhance feature processing and improve accuracy. Additionally, we introduce a trainable weight array to control the importance of each Transformer module for better generalization of the model. Experimental results demonstrate our model's effectiveness, with an accuracy rate of 99.58% for the public dataset Birds_data, as well as 98.77% for the Birdsonund1 dataset, and 99.03% for the UrbanSound8K environment sound dataset. [ABSTRACT FROM AUTHOR]

The pinyon jay Gymnorhinus cyanocephalus is listed as Vulnerable by the IUCN Red List of Threatened Species due to its continued decline in the wild caused by impacts to its unique pinyon-juniper woodland habitat. Recent reviews do not mention commercial trade as a threat and no information is given on use and trade at all. Here we provide evidence of recent international trade in pinyon jays observed in the European Union. We recommend listing the species in Appendix III of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to enable the monitoring of international trade. Additionally, the desirability of a listing in a higher appendix of CITES at the next Conference of the Parties, as a more restrictive measure, should be assessed, as it may provide a necessary tool to prevent illegal international trade from becoming an additional threat for this unique North American songbird. [ABSTRACT FROM AUTHOR]

Assessing habitat quality is critical for migrating birds, with implications for fuel loading, predation risk and timing of departure. To efficiently distribute within stopover sites, migrants rely on various cues that facilitate habitat quality assessment. In this study, we conducted a playback experiment at a mid‐route stopover site to test the effects of vocal cues, specifically bird songs, on habitat redistribution during spring migration. To estimate the effect of bird songs on bird abundance we mist‐netted and ringed birds for 60 days on alternating playback treatment (playing songs of three sylviid warbler species) and no playback (control) days. A nearby site was used to control for fluctuations caused by migration waves. Overall, total bird abundance was significantly increased by the playback treatment. This increase resulted from the attraction of conspecifics (species whose songs were played) rather than of other species – sylviids or others. Correspondingly, species richness was seemingly unaffected. To investigate the relationship between internal‐state factors and the attraction to playback in the most abundantly attracted species, Eurasian Blackcap Sylvia atricapilla, we tested associations with age, sex and body condition index but found no significant effects, possibly because of the limited sample size. Our findings challenge established ideas regarding heterospecific attraction and contradict previous studies. Attraction to bird song is discussed in the context of geographical location, timing and internal drivers. Vocal cues, specifically bird songs, may affect micro‐habitat selection by migrating songbirds during stopovers. Consequently, we call for consideration of the influence of the acoustic environment on birds during migratory stopover in future studies, habitat management and conservation efforts. [ABSTRACT FROM AUTHOR]

We propose an experimental paradigm to examine acoustic features responsible for song preference and recognition in songbirds. Song preference in female songbirds is often influenced by early song experience. That is why several Estrildid species, including our subject species, the Java sparrow (Padda oryzivora), are known to show an imprinted preference for their father's songs. After confirming that Java sparrow females preferred their father's song compared to nonimprinted through song playbacks (first step), we repeated the playback tests in the same subjects using synthesized stimuli (second step). To create synthesized stimuli, we removed all the complex frequency modulations and subharmonics from song notes that we used for the first step playback tests to see the effect of spectrometric features on song recognition. The results indicated that females showed higher rate of calling towards synthesized father song stimuli, suggesting that the macroscopic patterns would play more important roles in song recognition than the microscopic acoustic features. Although we looked at spectrometric features and father-imprinted song preference in this study, similar testing can be applied in many ways to test preference for local dialects or subspecies-specific songs. [ABSTRACT FROM AUTHOR]

Active sensing is a behavioral strategy for exploring the environment. In this study, we show that contact vocal behaviors can be an active sensing mechanism that uses sampling to gain information about the social environment, in particular, the vocal behavior of others. With a focus on the real-time vocal interactions of marmoset monkeys, we contrast active sampling to a vocal accommodation framework in which vocalizations are adjusted simply to maximize responses. We conduct simulations of a vocal accommodation and an active sampling policy and compare them with actual vocal interaction data. Our findings support active sampling as the best model for real-time marmoset monkey vocal exchanges. In some cases, the active sampling model was even able to partially predict the distribution of vocal durations for individuals to approximate the optimal call duration. These results suggest a non-traditional function for primate vocal interactions in which they are used by animals to seek information about their social environments. Modeling and data show that marmoset monkeys use active sensing to acquire social information from conspecifics; this challenges traditional views of primate communication. [ABSTRACT FROM AUTHOR]

Pathogen epidemics are key threats to human and wildlife health. Across systems, host protection from pathogens following initial exposure is often incomplete, resulting in recurrent epidemics through partially-immune hosts. Variation in population-level protection has important consequences for epidemic dynamics, but how acquired protection influences inter-individual heterogeneity in susceptibility and its epidemiological consequences remains understudied. We experimentally investigated whether prior exposure (none, low-dose, or high-dose) to a bacterial pathogen alters host heterogeneity in susceptibility among songbirds. Hosts with no prior pathogen exposure had little variation in protection, but heterogeneity in susceptibility was significantly augmented by prior pathogen exposure, with the highest variability detected in hosts given high-dose prior exposure. An epidemiological model parameterized with experimental data found that heterogeneity in susceptibility from prior exposure more than halved epidemic sizes compared with a homogeneous population with identical mean protection. However, because infection-induced mortality was also greatly reduced in hosts with prior pathogen exposure, reductions in epidemic size were smaller than expected in hosts with prior exposure. These results highlight the importance of variable protection from prior exposure and/or vaccination in driving population-level heterogeneity and epidemiological dynamics. Author summary: Individuals in a population are often highly variable in whether or not they get sick during an outbreak. This variability between individuals has important consequences for how widely a disease can spread. Therefore, it is useful to understand what drives the amount of variability in susceptibility present in populations as a whole. Because individuals in a population can have quite variable immune responses to the same type and dose of pathogen infection, one possibility is that populations of individuals with acquired immune protection from prior pathogen exposure are actually more variable in their susceptibility than populations of individuals with no previous pathogen infection. We tested this possibility using a songbird disease system as a model. We found that populations of birds for which we had generated immune protection by exposing them to a bacterial pathogen were far more variable in their susceptibility than birds that had never been infected before. We also show that this population-level variability in itself can strongly reduce the size of disease outbreaks. [ABSTRACT FROM AUTHOR]

We investigated how detectability and vocalization patterns of Saipan Reed Warblers (Acrocephalus hiwae) varied by time of day. We used long-duration sound recordings from 11 locations occupied by Saipan Reed Warblers to model the probability of detecting a vocalization in each hour of the day. We found that Saipan Reed Warblers sang during all daylight hours. We did not find evidence of a dawn chorus in this species. These results are useful for determining what time of day surveys of Saipan Reed Warblers should be conducted, which is particularly relevant because Saipan Reed Warblers are protected by local and U.S. Federal laws, which leads to frequent surveys for this species. [ABSTRACT FROM AUTHOR]

To reduce costs associated with nest building, some birds steal (kleptoparasitize) nest material. While this behavior is rarely reported in solitary nesting birds, it has been previously documented in 2 species of white-eyes, the Japanese White-eye (Zosterops japonicus) and the Indian White-eye (Z. palpebrosus). During surveys for Tinian Monarchs (Monarcha takatsukasae) on Tinian Island in the Northern Mariana Islands, we documented nest material kleptoparasitism by the Bridled White-eye (Z. conspicillatus). Through camera-trap footage and real-time observation, we observed Bridled White-eyes stealing material from 2 other forest bird species: the Micronesian Rufous Fantail (Rhipidura versicolor; n = 1 observation) and Tinian Monarch (n = 7). We documented nest material piracy during multiple nesting phases including building, incubation, and post-fledge, and from abandoned and depredated nests. This behavior was previously undocumented in the Bridled White-eye, and nest material kleptoparasitism is not documented in any other forest birds in the Mariana Islands. Kleptoparasitism of nest material has been known to cause destruction or abandonment of the host's nest. Given the potential implications of nest material kleptoparasitism on host nesting behavior and success, and that the Bridled White-eye is estimated to be the most abundant forest bird on Tinian, our observations warrant inquiry into how this behavior could be affecting the broader ecology of forest birds in the Mariana Islands. [ABSTRACT FROM AUTHOR]