Foraging behaviour and habitat use during chick-rearing in the Australian endemic black-faced cormorant (Phalacrocorax fuscescens).

Despite its wide distribution, relatively little is known of the foraging ecology and habitat use of the black-faced cormorant (Phalacrocorax fuscescens), an Australian endemic seabird. Such information is urgently required in view of the rapid oceanic warming of south-eastern Australia, the stronghold of the species. The present study used a combination of opportunistically collected regurgitates and GPS/dive behaviour data loggers to investigate diet, foraging behaviour and habitat-use of black-faced cormorants during four chick-rearing periods (2020-2023) on Notch Island, northern Bass Strait. Observed prey species were almost exclusively benthic (95%), which is consistent with the predominantly benthic diving behaviour recorded. Males foraged at deeper depths than females (median depth males: 18 m; median depth females: 8 m), presumably due to a greater physiological diving capacity derived from their larger body size. This difference in dive depths was associated with sexual segregation of foraging locations, with females predominantly frequenting shallower areas closer to the coastline. These findings have strong implications for the management of the species, as impacts of environmental change may disproportionally affect the foraging range of one sex and, thereby, reproductive success.

Metabolic adjustments to winter severity in two geographically separated great tit (Parus major) populations.

Understanding the potential limits placed on organisms by their ecophysiology is crucial for predicting their responses to varying environmental conditions. A main hypothesis for explaining avian thermoregulatory mechanisms is the aerobic capacity model, which posits a positive correlation between basal (basal metabolic rate [BMR]) and summit (Msum) metabolism. Most evidence for this hypothesis, however, comes from interspecific comparisons, and the ecophysiological underpinnings of avian thermoregulatory capacities hence remain controversial. Indeed, studies have traditionally relied on between-species comparisons, although, recently, there has been a growing recognition of the importance of intraspecific variation in ecophysiological responses. Therefore, here, we focused on great tits (Parus major), measuring BMR and Msum during winter in two populations from two different climates: maritime-temperate (Gontrode, Belgium) and continental (Zvenigorod, Russia). We tested for the presence of intraspecific geographical variation in metabolic rates and assessed the predictions following the aerobic capacity model. We found that birds from the maritime-temperate climate (Gontrode) showed higher BMR, whereas conversely, great tits from Zvenigorod showed higher levels of Msum. Within each population, our data did not fully support the aerobic capacity model's predictions. We argued that the decoupling of BMR and Msum observed may be caused by different selective forces acting on these metabolic rates, with birds from the continental-climate Zvenigorod population facing the need to conserve energy for surviving long winter nights (by keeping their BMR at low levels) while simultaneously being able to generate more heat (i.e., a high Msum) to withstand cold spells.

Cooperative breeding alters physiological and behavioral responses to habitat fragmentation.

Animals respond to habitat alteration with changes in their behavior and physiology. These changes determine individual performance and thus precede changes in population size. They are therefore hypothesized to provide important insights into how animals cope with environmental change. Here, we investigated physiological and behavioral responses of a cooperatively breeding bird, the placid greenbul (Phyllastrephus placidus), in a severely fragmented tropical biodiversity hotspot and combined these data with remotely sensed (LiDAR) environmental data. We found that individuals had increased glucocorticoid hormone levels when breeding in territories with low native canopy cover or located within small fragments. However, when breeding with the help of subordinates, breeders in low quality territories had similar glucocorticoid levels as those in higher quality territories. Our study shows that sociality may impact how well animals cope with environmental change and contributes to our understanding of the role of glucocorticoid physiology and behavior in response to anthropogenic change.

Great tits (Parus major) in a west European temperate forest show little seasonal variation in metabolic energy requirements.

Understanding how birds annually allocate energy to cope with changing environmental conditions and physiological states is a crucial question in avian ecology. There are several hypotheses to explain species' energy allocation. One prominent hypothesis suggests higher energy expenditure in winter due to increased thermoregulatory costs. The "reallocation" hypothesis suggests no net difference in seasonal energy requirements, while the "increased demand" hypothesis predicts higher energy requirements during the breeding season. Birds are expected to adjust their mass and/or metabolic intensity in ways that are consistent with their energy requirements. Here, we look for metabolic signatures of seasonal variation in energy requirements of a resident passerine of a temperate-zone (great tit, Parus major). To do so, we measured whole-body and mass-independent basal (BMR), summit (Msum), and field (FMR) metabolic rates during late winter and during breeding in Belgian great tits. During the breeding season, birds had on average 10% higher whole-body BMR and FMR compared to winter, while their Msum decreased by 7% from winter to breeding. Mass-independent metabolic rates showed a 10% increase in BMR and a 7% decrease in Msum from winter to breeding. Whole-body BMR was correlated with Msum, but this relationship did not hold for mass-independent metabolic rates. The modest seasonal change we observed suggests that great tits in our temperature study area maintain a largely stable energy budget throughout the year, which appears mostly consistent with the reallocation hypothesis.

Biophysical models accurately characterize the thermal energetics of a small invasive passerine bird.

Effective management of invasive species requires accurate predictions of their invasion potential in different environments. By considering species' physiological tolerances and requirements, biophysical mechanistic models can potentially deliver accurate predictions of where introduced species are likely to establish. Here, we evaluate biophysical model predictions of energy use by comparing them to experimentally obtained energy expenditure (EE) and thermoneutral zones (TNZs) for the common waxbill Estrilda astrild, a small-bodied avian invader. We show that biophysical models accurately predict TNZ and EE and that they perform better than traditional time-energy budget methods. Sensitivity analyses indicate that body temperature, metabolic rate, and feather characteristics were the most influential traits affecting model accuracy. This evaluation of common waxbill energetics represents a crucial step toward improved parameterization of biophysical models, eventually enabling accurate predictions of invasion risk for small (sub)tropical passerines.

Nutrient intake and its possible drivers in free-ranging European brown bears (Ursus arctos arctos).

The dietary nutrient profile has metabolic significance and possibly contributes to species' foraging behavior. The brown bear (Ursus arctos) was used as a model species for which dietary ingredient and nutrient concentrations as well as nutrient ratios were determined annually, seasonally and per reproductive class. Brown bears had a vertebrate- and ant-dominated diet in spring and early summer and a berry-dominated diet in fall, which translated into protein-rich and carbohydrate-rich diets, respectively. Fiber concentrations appeared constant over time and averaged at 25% of dry matter intake. Dietary ingredient proportions differed between reproductive classes; however, these differences did not translate into a difference in dietary nutrient concentrations, suggesting that bears manage to maintain similar nutrient profiles with selection of different ingredients. In terms of nutrient ratios, the dietary protein to non-protein ratio, considered optimal at around 0.2 (on metabolizable energy basis), averaged around 0.2 in this study in fall and around 0.8 in spring and summer. We introduced the minimal non-fat to fat ratio necessary for efficient maintenance metabolism. This ratio varied across seasons but never fell beneath the theoretically estimated minimum to ensure metabolic efficiency. This population thus managed to ingest diets that never exerted a lack of glucogenic substrate, suggesting that metabolic efficiency may either be a driver of active diet selection or that natural resources available to bears did not constitute a constraint in this respect. Given the considerable proportion of fiber in the diet of brown bears, the relevance of this nutrient and its role in foraging behavior might be underestimated.

The influence of vegetation structure on sleeping site selection by chimpanzees (Pan troglodytes troglodytes).

Sleep is an important aspect of great ape life; these animals build sleeping platforms every night. In a community of chimpanzees, each subgroup selects a sleeping site where each individual builds a sleeping platform, mostly on a tree. Previous studies have measured the heights of sleeping platforms and sleeping trees to test the predation avoidance and thermoregulation hypotheses of sleeping site selection. However, it remains unclear how components of vegetation structure (vertical and horizontal) together determine the selection of sleeping sites by chimpanzees. Using botanical inventories around sleeping sites in a tropical rainforest of Cameroon, we found that chimpanzees preferentially sleep in trees measuring 40-50 cm in diameter. Regarding height, on average, sleeping trees measured 26 m and sleeping platforms were built at 16 m. To build sleeping platforms, chimpanzees preferred four tree species, which represent less than 3% of tree species in the study area. We demonstrate that the variation in abundance of tree species and the vertical and horizontal structure of the vegetation drive chimpanzee sleeping site selection. It was previously thought that preference for vegetation types was the driver of sleeping site selection in chimpanzees. However, results from this study indicate that the importance of vegetation types in sleeping site selection depends on their botanical characteristics including the variation in tree size, the abundance of all trees, the abundance of sleeping trees, and the occurrence of preferred sleeping tree species, which predict sleeping site selection. The height and diameter of trees are considered by chimpanzees when selecting a particular tree for sleeping and when selecting a site with a specific vertical structure. In addition to tree height, the abundance of smaller neighboring trees may also play a role in the chimpanzee antipredation strategy. Our results demonstrate that chimpanzees consider several vegetation parameters to establish sleeping sites.

Mechanistic models project bird invasions with accuracy.

Invasive species pose a major threat to biodiversity and inflict massive economic costs. Effective management of bio-invasions depends on reliable predictions of areas at risk of invasion, as they allow early invader detection and rapid responses. Yet, considerable uncertainty remains as to how to predict best potential invasive distribution ranges. Using a set of mainly (sub)tropical birds introduced to Europe, we show that the true extent of the geographical area at risk of invasion can accurately be determined by using ecophysiological mechanistic models that quantify species' fundamental thermal niches. Potential invasive ranges are primarily constrained by functional traits related to body allometry and body temperature, metabolic rates, and feather insulation. Given their capacity to identify tolerable climates outside of contemporary realized species niches, mechanistic predictions are well suited for informing effective policy and management aimed at preventing the escalating impacts of invasive species.

Seasonal variation in thermoregulatory capacity of three closely related Afrotropical Estrildid finches introduced to Europe.

A species' potential geographical range is largely determined by how the species responds physiologically to its changing environment. It is therefore crucial to study the physiological mechanisms that species use to maintain their homeothermy in order to address biodiversity conservation challenges, such as the success of invasions of introduced species. The common waxbill Estrilda astrild, the orange-cheeked waxbill E. melpoda, and the black-rumped waxbill E. troglodytes are small Afrotropical passerines that have established invasive populations in regions where the climate is colder than in their native ranges. As a result, they are highly suitable species for studying potential mechanisms for coping with a colder and more variable climate. Here, we investigated the magnitude and direction of seasonal variation in their thermoregulatory traits, such as basal (BMR), summit (Msum) metabolic rates and thermal conductance. We found that, from summer to autumn, their ability to resist colder temperatures increased. This was not related to larger body masses or higher BMR and Msum, but instead, species downregulated BMR and Msum toward the colder season, suggesting energy conservation mechanisms to increase winter survival. BMR and Msum were most strongly correlated with temperature variation in the week preceding the measurements. Common waxbill and black-rumped waxbill, whose native ranges encompass the highest degree of seasonality, showed the most flexibility in metabolic rates (i.e., stronger downregulation toward colder seasons). This ability to adjust thermoregulatory traits, combined with increased cold tolerance, may facilitate their establishment in areas characterized by colder winters and less predictable climates.

Widespread triazole pesticide use affects infection dynamics of a global amphibian pathogen.

The sixth mass extinction is a consequence of complex interplay between multiple stressors with negative impact on biodiversity. We here examine the interaction between two globally widespread anthropogenic drivers of amphibian declines: the fungal disease chytridiomycosis and antifungal use in agriculture. Field monitoring of 26 amphibian ponds in an agricultural landscape shows widespread occurrence of triazole fungicides in the water column throughout the amphibian breeding season, together with a negative correlation between early season application of epoxiconazole and the prevalence of chytrid infections in aquatic newts. While triazole concentrations in the ponds remained below those that inhibit growth of Batrachochytrium dendrobatidis, they bioaccumulated in the newts' skin up to tenfold, resulting in cutaneous growth-suppressing concentrations. As such, a concentration of epoxiconazole, 10 times below that needed to inhibit fungal growth, prevented chytrid infection in anuran tadpoles. The widespread presence of triazoles may thus alter chytrid dynamics in agricultural landscapes.

Zoonotic pathogens linked with hedgehog diphtheric disease.

Hedgehog diphtheric disease (HDD), an ulcerative skin disease with a high fatality rate, is an emerging threat to European hedgehogs (Erinaceus europaeus). We explored the potential role of a panel of zoonotic pathogens in the presumed multifactorial nature of HDD in 188 hedgehogs from 3 wildlife rescue centres in Belgium. As expected, and with a prevalence of 67% in 57 hedgehogs with skin lesions, characteristic of HDD, the occurrence of Corynebacterium ulcerans was strongly associated with the disease. Remarkably, with a prevalence of 42% in affected animals, infections with Borrelia burgdorferi sensu lato were 3.92 times more likely to be detected in HDD (95% confidence interval: 1.650-9.880; p = .0024). Overall, 40 hedgehogs tested positive for the B. burgdorferi sensu lato complex, including Borrelia afzelii (n = 30), Borrelia bavariensis (n = 7) and Borrelia spielmanii (n = 7). Other widely occurring pathogens included Salmonella (prevalence of 19%, with three pulsed-field gel electrophoresis profiles) and Leptospira sp. (prevalence of 11%, including Leptospira interrogans and Leptospira borgpetersenii), but these were not associated with the occurrence of HDD. These findings show that hedgehogs in Belgium represent a significant reservoir of multiple zoonotic bacteria, of which toxigenic C. ulcerans and B. burgdorferi sensu lato are associated with widespread hedgehog skin pathology and mortality.

Growing up in a crowd: social environment shapes the offspring's early exploratory phenotype in a colonial breeding species.

In colonial breeding species, the number of adverse social interactions during early life typically varies with breeding density. Phenotypic plasticity can help deal with this social context, by allowing offspring to adjust their behaviour. Furthermore, offspring may not be unprepared since mothers can allocate resources to their embryos that may pre-adjust them to the post-hatching conditions. Thus, we hypothesize that lesser black-backed gull chicks raised in dense breeding areas, with greater exposure to intra-specific aggression, show higher levels of anxiety and lower levels of exploration compared to chicks in low-density areas, and that this is facilitated by prenatal effects. To test this, we cross-fostered clutches within and across pre-defined high- and low-breeding density areas. We measured chicks' anxiety and exploration activity in an open-field test that included a novel and a familiar object. We found that both pre- and post-natal social environment contributed nearly equally and shaped the offspring's exploratory behaviour, but not its anxiety, in an additive way. Post-natal effects could reflect a learned avoidance of intra-specific aggression, yet identifying the pathways of the prenatal effects will require further study.

Hybridization may aid evolutionary rescue of an endangered East African passerine.

Introgressive hybridization is a process that enables gene flow across species barriers through the backcrossing of hybrids into a parent population. This may make genetic material, potentially including relevant environmental adaptations, rapidly available in a gene pool. Consequently, it has been postulated to be an important mechanism for enabling evolutionary rescue, that is the recovery of threatened populations through rapid evolutionary adaptation to novel environments. However, predicting the likelihood of such evolutionary rescue for individual species remains challenging. Here, we use the example of Zosterops silvanus, an endangered East African highland bird species suffering from severe habitat loss and fragmentation, to investigate whether hybridization with its congener Zosterops flavilateralis might enable evolutionary rescue of its Taita Hills population. To do so, we employ an empirically parameterized individual-based model to simulate the species' behaviour, physiology and genetics. We test the population's response to different assumptions of mating behaviour and multiple scenarios of habitat change. We show that as long as hybridization does take place, evolutionary rescue of Z. silvanus is likely. Intermediate hybridization rates enable the greatest long-term population growth, due to trade-offs between adaptive and maladaptive introgressed alleles. Habitat change did not have a strong effect on population growth rates, as Z. silvanus is a strong disperser and landscape configuration is therefore not the limiting factor for hybridization. Our results show that targeted gene flow may be a promising avenue to help accelerate the adaptation of endangered species to novel environments, and demonstrate how to combine empirical research and mechanistic modelling to deliver species-specific predictions for conservation planning.

Tree Species Diversity and Forest Edge Density Jointly Shape the Gut Microbiota Composition in Juvenile Great Tits (Parus major).

Despite the microbiome's key role in health and fitness, little is known about the environmental factors shaping the gut microbiome of wild birds. With habitat fragmentation being recognised as a major threat to biological diversity, we here determined how forest structure influences the bacterial species richness and diversity of wild great tit nestlings (Parus major). Using an Illumina metabarcoding approach which amplifies the 16S bacterial ribosomal RNA gene, we measured gut microbiota diversity and composition from 49 great tit nestlings, originating from 23 different nests that were located in 22 different study plots across a gradient of forest fragmentation and tree species diversity. Per nest, an average microbiome was determined on which the influence of tree species (composition and richness) and forest fragmentation (fragment area and edge density) was examined and whether this was linked to host characteristics (body condition and fledging success). We found an interaction effect of edge density with tree species richness or composition on both the microbial richness (alpha diversity: Chao1 and Shannon) and community structure (beta diversity: weighted and unweighted UniFrac). No significant short-term impact was observed of the overall faecal microbiome on host characteristics, but rather an adverse effect of specific bacterial genera on fledging success. These results highlight the influence of environmental factors on the microbial richness as well as the phylogenetic diversity during a life stage where the birds' microbiota is shaped, which could lead to long-term consequences for host fitness.

Impact of heavy metal exposure on biological control of a deadly amphibian pathogen by zooplankton.

Despite devastating effects on global biodiversity, efficient mitigation strategies against amphibian chytridiomycosis are lacking. Since the free-living pathogenic zoospores of Batrachochytrium dendrobatidis (Bd), the infective stage of this disease, can serve as a nutritious food source for components of zooplankton communities, these groups may act as biological control agents by eliminating zoospores from the aquatic environment. Such pathogen-predator interaction is, however, embedded in the aquatic food web structure and is therefore affected by abiotic factors interfering with these networks. Heavy metals, released from both natural and anthropogenic sources, are widespread contaminants of aquatic ecosystems and may interfere with planktonic communities and thus pathogen elimination rates. We investigated the interaction between zooplankton communities and chytridiomycosis infections in a Flemish agricultural region. Moreover, we also investigated the impact of heavy metal contamination, that was previously investigated in the region and presented in recent work, on zooplankton assemblages and chytridiomycosis infections. Finally, we tested the effect of sublethal concentrations of copper and zinc on Bd removal rates by Daphnia magna in a laboratory assay. Although zinc, copper, nickel and chromium were widely abundant pollutants, heavy metals were no driving force for zooplankton assemblages at our study locations. Moreover, our field survey did not reveal indirect effects of zooplankton assemblages on chytridiomycosis infections. However, sampling occasions testing negative for Bd showed a higher degree of copper contamination compared to positive sampling occasions, indicating a potential inhibitory effect of copper on Bd prevalence. Finally, whereas D. magna significantly reduced zoospore densities in its environment, sublethal concentrations of copper and zinc showed no interference with pathogen removal in the laboratory assay. Our results provide perspectives for further research on such a biological control strategy against chytridiomycosis by optimizing environmental conditions for pathogen predation.

Diet diversity and environment determine the intestinal microbiome and bacterial pathogen load of fire salamanders.

Diverse communities of symbiotic microbes inhabit the digestive systems of vertebrates and play a crucial role in animal health, and host diet plays a major role in shaping the composition and diversity of these communities. Here, we characterized diet and gut microbiome of fire salamander populations from three Belgian forests. We carried out DNA metabarcoding on fecal samples, targeting eukaryotic 18S rRNA of potential dietary prey items, and bacterial 16S rRNA of the concomitant gut microbiome. Our results demonstrated an abundance of soft-bodied prey in the diet of fire salamanders, and a significant difference in the diet composition between males and females. This sex-dependent effect on diet was also reflected in the gut microbiome diversity, which is higher in males than female animals. Proximity to human activities was associated with increased intestinal pathogen loads. Collectively, the data supports a relationship between diet, environment and intestinal microbiome in fire salamanders, with potential health implications.

Simultaneous GPS-tracking of parents reveals a similar parental investment within pairs, but no immediate co-adjustment on a trip-to-trip basis.

BACKGROUND: Parental care benefits the offspring, but comes at a cost for each parent, which in biparental species gives rise to a conflict between partners regarding the within-pair distribution of care. Pair members could avoid exploitation by efficiently keeping track of each other's efforts and coordinating their efforts. Parents may, therefore, space their presence at the nest, which could also allow for permanent protection of the offspring. Additionally, they may respond to their partner's previous investment by co-adjusting their efforts on a trip-to-trip basis, resulting in overall similar parental activities within pairs. METHODS: We investigated the coordination of parental care measured as nest attendance and foraging effort in the Lesser black-backed gull (Larus fuscus), a species with long nest bouts that performs extended foraging trips out of sight of their partner. This was achieved by GPS-tracking both pair members simultaneously during the entire chick rearing period. RESULTS: We found that the timing of foraging trips (and hence nest attendance) was coordinated within gull pairs, as individuals left the colony only after their partner had returned. Parents did not match their partner's investment by actively co-adjusting their foraging efforts on a trip-by-trip basis. Yet, pair members were similar in their temporal and energetic investments during chick rearing. CONCLUSION: Balanced investment levels over a longer time frame suggest that a coordination of effort may not require permanent co-adjustment of the levels of care on a trip-to-trip basis, but may instead rather take place at an earlier stage in the reproductive attempt, or over integrated longer time intervals. Identifying the drivers and underlying processes of coordination will be one of the next necessary steps to fully understand parental cooperation in long-lived species.

Body size and tree species composition determine variation in prey consumption in a forest-inhabiting generalist predator.

Trophic interactions may strongly depend on body size and environmental variation, but this prediction has been seldom tested in nature. Many spiders are generalist predators that use webs to intercept flying prey. The size and mesh of orb webs increases with spider size, allowing a more efficient predation on larger prey. We studied to this extent the orb-weaving spider Araneus diadematus inhabiting forest fragments differing in edge distance, tree diversity, and tree species. These environmental variables are known to correlate with insect composition, richness, and abundance. We anticipated these forest characteristics to be a principle driver of prey consumption. We additionally hypothesized them to impact spider size at maturity and expect shifts toward larger prey size distributions in larger individuals independently from the environmental context. We quantified spider diet by means of metabarcoding of nearly 1,000 A. diadematus from a total of 53 forest plots. This approach allowed a massive screening of consumption dynamics in nature, though at the cost of identifying the exact prey identity, as well as their abundance and putative intraspecific variation. Our study confirmed A. diadematus as a generalist predator, with more than 300 prey ZOTUs detected in total. At the individual level, we found large spiders to consume fewer different species, but adding larger species to their diet. Tree species composition affected both prey species richness and size in the spider's diet, although tree diversity per se had no influence on the consumed prey. Edges had an indirect effect on the spider diet as spiders closer to the forest edge were larger and therefore consumed larger prey. We conclude that both intraspecific size variation and tree species composition shape the consumed prey of this generalist predator.

Salamander loss alters litter decomposition dynamics.

Biodiversity loss affects ecosystem functioning. Top down effects of amphibian declines on the trophic food web of the forest floor are poorly understood. Here we quantify and explain the effects of disease-driven loss of salamanders on the dynamics of forest leaf litter. Using paired mesocosms, within a Belgian forest, we tested the effect of fire salamander (Salamandra salamandra) presence on the trophic cascade that results in the decomposition rate of good quality (maple - Acer pseudoplatanus) and poorer quality (oak - Quercus robur) leaf litter, over an 18 month period. The presence of salamanders reduced decomposition rate of Quercus litter up to 20%. This was associated with a significantly higher predation rate on detritivores, which altered the functional composition of the invertebrate community. Functional composition analysis of the litter microbiome showed less bacteria associated with leaf litter degradation on the Quercus litter in the presence of salamanders. Salamanders thus influence ecosystem functions through trophic cascades and promote the retention of the leaf litter fraction in poorer quality litter.

Exploring the faecal microbiome of the Eurasian nuthatch (Sitta europaea).

Gastrointestinal microbiota fulfill pivotal roles in providing a host with nutrition and protection from pathogenic microorganisms. Up to date, most microbiota research has focused on humans and other mammals, whereas birds and especially wild birds lag behind. Within the field of the avian gut microbiome, research is heavily biased towards poultry. In this study, we analyzed the gut microbiome of the Eurasian nuthatch (Sitta europaea), using faecal samples of eight nestlings originating from three nuthatch nests in the south of Ghent (Belgium), using Illumina sequencing of the 16S rRNA gene. Relative frequency analysis showed a dominance of Firmicutes and Actinobacteria and to a lesser extent Proteobacteria. Bacteroidetes and other phyla were relatively rare. At higher taxonomic levels, a high degree of inter-individual variation in terms of overall microbiota community structure as well as dominance of certain bacteria was observed, but with a higher similarity for the nestlings sharing the same nest. When comparing the nuthatch faecal microbiome to that of great tit nestlings that were sampled during the same breeding season and in the same forest fragment, differences in the microbial community structure were observed, revealing distinct dissimilarities in the relative abundancy of taxa between the two bird species. This study is the first report on the nuthatch microbiome and serves as a reference study for nuthatch bacterial diversity and can be used for targeted screening of the composition and general functions of the avian gut microbiome.