Developmental stage-dependent effects of perceived predation risk on nestling tree swallows (Tachycineta bicolor).

The risk of predation directly affects the physiology, behavior, and fitness of wild birds. Strong social connections with conspecifics could help individuals recover from a stressful experience such as a predation event; however, competitive interactions also have the potential to exacerbate stress. Few studies have investigated the interaction between environmental stressors and the social landscape in wild bird populations. In 2 years of field studies, we experimentally simulated predation attempts on breeding female tree swallows (Tachicyneta bicolor). At the same time, we manipulated female breast plumage color, a key social signal. Simulated predation events on tree swallows early in the nestling period reduced young nestlings' mass by approximately 20% and shortened telomere lengths. Ultimately, only 31% of nestlings in the predation group fledged compared with 70% of control nestlings. However, the effects of experimental manipulations were timing dependent: the following year when we swapped the order of the experimental manipulations and simulated predation during incubation, there were no significant effects of predation on nestling condition or fledging success. Contrary to our expectations, manipulation of the social environment did not affect the response of tree swallows to simulated predation. However, manipulating female plumage during the nestling period did reduce nestling skeletal size and mass, although the effects depended on original plumage brightness. Our data demonstrate that transient stressors on female birds can have carry-over effects on their nestlings if they occur during critical periods in the breeding season.

Neurogenomic landscape associated with status-dependent cooperative behaviour.

The neurogenomic mechanisms mediating male-male reproductive cooperative behaviours remain unknown. We leveraged extensive transcriptomic and behavioural data on a neotropical bird species (Pipra filicauda) that performs cooperative courtship displays to understand these mechanisms. In this species, the cooperative display is modulated by testosterone, which promotes cooperation in non-territorial birds, but suppresses cooperation in territory holders. We sought to understand the neurogenomic underpinnings of three related traits: social status, cooperative display behaviour and testosterone phenotype. To do this, we profiled gene expression in 10 brain nuclei spanning the social decision-making network (SDMN), and two key endocrine tissues that regulate social behaviour. We associated gene expression with each bird's behavioural and endocrine profile derived from 3 years of repeated measures taken from free-living birds in the Ecuadorian Amazon. We found distinct landscapes of constitutive gene expression were associated with social status, testosterone phenotype and cooperation, reflecting the modular organization and engagement of neuroendocrine tissues. Sex-steroid and neuropeptide signalling appeared to be important in mediating status-specific relationships between testosterone and cooperation, suggesting shared regulatory mechanisms with male aggressive and sexual behaviours. We also identified differentially regulated genes involved in cellular activity and synaptic potentiation, suggesting multiple mechanisms underpin these genomic states. Finally, we identified SDMN-wide gene expression differences between territorial and floater males that could form the basis of 'status-specific' neurophysiological phenotypes, potentially mediated by testosterone and growth hormone. Overall, our findings provide new, systems-level insights into the mechanisms of cooperative behaviour and suggest that differences in neurogenomic state are the basis for individual differences in social behaviour.

Social signal manipulation and environmental challenges have independent effects on physiology, internal microbiome, and reproductive performance in tree swallows (Tachycineta bicolor).

The social environment that individuals experience appears to be a particularly salient mediator of stress resilience, as the nature and valence of social interactions are often related to subsequent health, physiology, microbiota, and overall stress resilience. Relatively few studies have simultaneously manipulated the social environment and ecological challenges under natural conditions. Here, we report the results of experiments in wild tree swallows (Tachycineta bicolor) in which we manipulated both ecological challenges (predator encounters and flight efficiency reduction) and social interactions (by experimental dulling of a social signal). In two experiments conducted in separate years, we reversed the order of these treatments so that females experienced either an altered social signal followed by a challenge or vice-versa. Before, during, and after treatments were applied, we tracked breeding success, morphology and physiology (mass, corticosterone, and glucose), nest box visits via an RFID sensor network, cloacal microbiome diversity, and fledging success. Overall, we found that predator exposure during the nestling period reduced the likelihood of fledging and that signal manipulation sometimes altered nest box visitation patterns, but little evidence that the two categories of treatment interacted with each other. We discuss the implications of our results for understanding what types of challenges and what conditions are most likely to result in interactions between the social environment and ecological challenges.

Gut Microbiome as a Mediator of Stress Resilience: A Reactive Scope Model Framework.

Stress resilience is defined as the ability to rebound to a homeostatic state after exposure to a perturbation. Organisms modulate various physiological mediators to respond to unpredictable changes in their environment. The gut microbiome is a key example of a physiological mediator that coordinates a myriad of host functions including counteracting stressors. Here, we highlight the gut microbiome as a mediator of host stress resilience in the framework of the reactive scope model. The reactive scope model integrates physiological mediators with unpredictable environmental changes to predict how animals respond to stressors. We provide examples of how the gut microbiome responds to stressors within the four ranges of the reactive scope model (i.e., predictive homeostasis, reactive homeostasis, homeostatic overload, and homeostatic failure). We identify measurable metrics of the gut microbiome that could be used to infer the degree to which the host is experiencing chronic stress, including microbial diversity, flexibility, and gene richness. The goal of this perspective piece is to highlight the underutilized potential of measuring the gut microbiome as a mediator of stress resilience in wild animal hosts.

Predictable and host-species specific humanization of the gut microbiota in captive primates.

Humans and nonhuman primates (NHPs) harbor complex gut microbial communities that affect phenotypes and fitness. The gut microbiotas of wild NHPs reflect their hosts' phylogenetic histories and are compositionally distinct from those of humans, but in captivity the endogenous gut microbial lineages of NHPs can be lost or replaced by lineages found in humans. Despite its potential contributions to gastrointestinal dysfunction, this humanization of the gut microbiota has not been investigated systematically across captive NHP species. Here, we show through comparisons of well-sampled wild and captive populations of apes and monkeys that the fraction of the gut microbiota humanized by captivity varies significantly between NHP species but is remarkably reproducible between captive populations of the same NHP species. Conspecific captive populations displayed significantly greater than expected overlap in the sets of bacterial 16S rRNA gene variants that were differentially abundant between captivity and the wild. This overlap was evident even between captive populations residing on different continents but was never observed between heterospecific captive populations. In addition, we developed an approach incorporating human gut microbiota data to rank NHPs' gut microbial clades based on the propensity of their lineages to be lost or replaced in captivity by lineages found in humans. Relatively few microbial genera displayed reproducible degrees of humanization in different captive host species, but most microbial genera were reproducibly humanized or retained from the wild in conspecific pairs of captive populations. These results demonstrate that the gut microbiotas of captive NHPs display predictable, host-species specific responses to captivity.

A virtual bird's eye view: Live streaming nest boxes to continue outreach in the era of COVID-19.

COVID-19 created a host of challenges for science education; in our case, the pandemic halted our in-person elementary school outreach project on bird biology. This project was designed as a year-long program to teach fifth-grade students in Ithaca, New York, USA, about bird ecology and biodiversity using in-person presentations, games, activities, and outdoor demonstrations. As a central part of this effort, we set up nest boxes on school property and planned to monitor them with students during bird breeding in the spring. Here, we describe our experiences transitioning this program online: we live streamed nest boxes to the students' virtual classroom and used them as a focal point for virtual lessons on bird breeding and nestling development. In an era of social distancing and isolation, we propose that nest box live streaming and virtual lessons can support communities by providing access to the outdoors and unconventional science learning opportunities for all students. Instituting similar programs at local schools has the potential to increase equitable learning opportunities for students across geographic locations and with varying degrees of physical access to the outdoors and nature.

Evidence supporting the microbiota-gut-brain axis in a songbird.

Recent research in mammals supports a link between cognitive ability and the gut microbiome, but little is known about this relationship in other taxa. In a captive population of 38 zebra finch(es) (Taeniopygia guttata), we quantified performance on cognitive tasks measuring learning and memory. We sampled the gut microbiome via cloacal swab and quantified bacterial alpha and beta diversity. Performance on cognitive tasks related to beta diversity but not alpha diversity. We then identified differentially abundant genera influential in the beta diversity differences among cognitive performance categories. Though correlational, this study provides some of the first evidence of an avian microbiota-gut-brain axis, building foundations for future microbiome research in wild populations and during host development.

Characterizing the microbiome of ectoparasitic louse flies feeding on migratory raptors.

Louse flies (Diptera: Hippoboscidae) are obligate ectoparasites that often cause behavioral, pathogenic, and evolutionary effects on their hosts. Interactions between ectoparasites and avian hosts, especially migrating taxa, may influence avian pathogen spread in tropical and temperate ecosystems and affect long-term survival, fitness and reproductive success. The purpose of this study was to characterize the vector-associated microbiome of ectoparasitic louse flies feeding on migrating raptors over the fall migration period. Surveys for louse flies occurred during fall migration (2015-2016) at a banding station in Pennsylvania, United States; flies were collected from seven species of migrating raptors, and we sequenced their microbial (bacteria and archaea) composition using high-throughput targeted amplicon sequencing of the 16S rRNA gene (V4 region). All louse flies collected belonged to the same species, Icosta americana. Our analysis revealed no difference in bacterial communities of louse flies retrieved from different avian host species. The louse fly microbiome was dominated by a primary endosymbiont, suggesting that louse flies maintain a core microbial structure despite receiving blood meals from different host species. Thus, our findings highlight the importance of characterizing both beneficial and potentially pathogenic endosymbionts when interpreting how vector-associated microbiomes may impact insect vectors and their avian hosts.

No evidence for a link between forest herbicides and offspring sex ratio in a migratory songbird using high-throughput molecular sexing.

Many species that use or require early-successional forest are of conservation concern, including a number of songbirds that have experienced long-term population declines. In this study, our initial goal was to test whether herbicide application intensity was linked to offspring sex ratio in the White-crowned Sparrow (Zonotrichia leucophrys), a species that requires early-successional forest within forested landscapes. However, a rapid and accurate method using direct PCR to sex a large sample of birds (n > 1000 individuals) was unavailable, so our secondary goal was to develop a new approach for rapidly determine offspring sex. We obtained blood samples from sparrow young during the 2013-2014 breeding seasons in regenerating conifer plantations that were treated with one of four treatments (i.e. light, moderate, and intensive herbicide application, or no-spray control). We then optimized a protocol that used a commercially available, direct PCR kit to amplify sex-specific fragments of the CHD (chromo-helicase-DNA-binding) genes directly from whole blood stored in lysis buffer. Using this approach, we found no evidence that offspring sex ratio was linked to herbicide application intensity or to food availability across herbicide treatments. Our molecular sexing technique was 100% accurate when validated on known-sex adults, and 99.9% of our blood samples amplified successfully after being stored in lysis buffer stored for up to 3 years. The application of direct PCR for sexing birds eliminated the need for DNA extraction and substantially reduced sample processing time, cost, and the opportunity for errors during the extraction step. We conclude that forest herbicide application intensity does not influence sparrow offspring sex ratio in our study system, and that our approach provides a rapid, accurate, and tractable method for sexing birds that can facilitate studies that require processing of a large number of samples.