Journal of Avian Biology最新文献

Ecophysiology has enhanced our understanding of avian migration, yet many aspects of how these processes interrelate are still unclear. Partially migratory populations provide an ideal framework for its study in the wild, since resident and migratory individuals coexist temporarily in the same area and face similar selection pressures. We focused on two Iberian populations of Eurasian hoopoe Upupa epops, a trans-Saharan long-distance migrant, to explore the links between the immune system and migratory behaviour. We determined the migratory status of individual hoopoes using stable isotope analysis of deuterium (²H) and measured a number of immunological parameters, including estimates of innate and adaptive immunity, as well as body condition, and muscle and fat stores. Our results indicate that resident hoopoes had higher IgY levels and higher muscle and fat stores compared to migrants during the breeding season. Moreover, we found seasonal variation in leukocyte profiles of resident birds, with higher heterophil/lymphocyte (H/L) ratios in winter than during the breeding season. We observed significantly higher H/L ratios and complement activity in resident males than in resident females, but not within migratory birds. Overall, we show differences in immune response linked to migratory behaviour in partial migratory populations. This study contributes to unraveling the associations between physiological status and migratory behaviour and ultimately helps to understand how different migratory strategies are maintained in partially migratory populations.

Long-distance bird migration is one of the most metabolically and immunologically challenging feats in the animal kingdom, with birds often needing to double their weight in a matter of days and facing increased exposure to novel pathogens. The physiological and behavioural adaptations required to survive such journeys may be facilitated by the gut microbiome, a diverse community of symbiotic microbes that produce rare nutrients, fatty acids, and immune compounds that can confer rapid physiological adaptations to changing environmental conditions. However, the causal role of the gut microbiome in regulating migration physiology remains a mystery. In this review, we synthesize current knowledge of gut microbiome composition and function during migration, outline possible mechanisms by which changes in the gut microbiome could benefit migrants, and identify future research priorities. We find that active migration is usually associated with reduced diversity of the gut microbiome and with the expansion of several study-specific taxa. Additionally, some microbial traits have been found to correlate with host condition and fat deposits during migration. However, there remains little understanding of how changes in the gut microbiome during migration relate to most physiological parameters, the molecular mechanisms linking the gut microbiome to host physiology during migration, or the underlying ecological, dietary, and intrinsic drivers of gut microbiome changes across the migratory cycle. Our review draws from examples across non-migratory systems to explore how gut microbiomes could adaptively regulate physiological traits relevant to migration. We highlight the need for studies that connect gut and circulating metabolites and for experimental studies that test the underlying drivers of gut microbial and metabolite dynamics in controlled settings. Given its diverse physiological demands and ubiquity, bird migration presents an excellent model system to investigate the adaptive potential of the gut microbiome in natural populations.

Interspecific territoriality is a prevalent form of interference competition among animals across environments. However, the connections between interspecific territorial aggression and other related aspects such as hybridization and climate remain unexplored. We investigated territorial aggression in two Neotropical wren species, Campylorhynchus zonatus brevirostris and C. fasciatus pallescens, along a precipitation gradient in western Ecuador using playback experiments. Campylorhynchus f. pallescens exhibits geographic variation: northern populations (C. f. pallescens north) are hybrids of C. z. brevirostris and C. f. fasciatus, while southern populations (C. f. pallescens south) show primary genetic admixture with C. f. fasciatus (from northeastern Peru). We pursued three objectives: 1) to compare intra- and inter-territorial aggression of C. z. brevirostris and the admixed C. f. pallescens north and south; 2) to assess territorial aggression across these three genetic clusters; and 3) to examine direct and indirect (via primary productivity) associations between climate and territorial aggression. We simulated territory intrusion using playback experiments and quantified aggressive responses using principal component analysis (PCA) to integrate three behavioral measurements: minimum approach distance to the stimulus, latency to reach this distance, and the number of aggressive displays (fixed action patterns). Admixed C. f. pallescens north displayed no significant differences in aggression across treatments, supporting the established trend of high interspecific territoriality in hybrids. Campylorhynchus f. pallescens south was the only genetic cluster that showed significant differences among treatments, exhibiting more pronounced aggressive responses to intraspecific stimuli and higher aggression than C. z. brevirostris and C. f. pallescens north. This pattern of dominance in territorial aggression contrasts with the previously reported direction of genetic introgression from C. z. brevirostris towards C. f. pallescens. Precipitation is related to aggression, potentially through resource availability. We emphasize the importance of understanding the interactions among hybridization, territoriality, and environmental stressors in tropical birds.

Uropygial secretion might play a crucial role in avian defense by exhibiting antimicrobial properties that protect birds from various pathogens. Although there has been considerable research, the differences in methods and results have led to varying conclusions about how well it works as an antimicrobial. Despite extensive research, the differences in experimental methods and results have led to varying conclusions regarding its antimicrobial effectiveness. This review consolidates existing literature on the antimicrobial activity of uropygial secretion or related compounds against bacteria and fungi across different bird species. A comprehensive search identified 35 studies, showcasing a variety of techniques used to assess antimicrobial activity, including agar diffusion, colony-forming unit (CFU) counting, and flow cytometry. The findings reveal a diverse range of antimicrobial effects influenced by bird species, target microorganisms, and the methodologies employed. Notably, uropygial secretion appears to be more effective against gram-positive bacteria than gram-negative bacteria and fungi, although these latter groups have been less extensively studied. The review also underscores significant limitations in taxonomic representation, as research has primarily focused on a limited number of bird species while many others remain underrepresented. Additionally, gaps in standardization and the predominance of in vitro studies hinder our ability to draw comprehensive conclusions about the antimicrobial potential of the uropygial secretions under natural conditions. Future research should prioritize standardizing methodologies, broadening the taxonomic scope, and investigating the combined effects of individual compounds within the secretion, including symbiotic microorganisms. Addressing these gaps will enhance our understanding of the evolutionary and ecological significance of uropygial secretion and clarify its role in avian health and defense mechanisms.

Brood parasitism can be costly to host fitness, which in turn may favour host strategies that decrease these costs. Duck (Anatinae) nests are often parasitized by eggs of other ducks, and one way that hosts can respond to potentially costly brood parasitism is to move parasitic eggs to the clutch periphery, where egg incubation temperatures can be suboptimal relative to the clutch centre. We explored whether red-breasted mergansers Mergus serrator use discriminatory egg incubation against parasitic eggs laid by conspecifics in a population where conspecific brood parasitism (CBP) is common. We used isoelectric focusing electrophoresis of egg albumen from entire clutches of 12 parasitized nests to identify parasitic eggs. A randomization test pooling identified parasitic eggs (n = 50) across nests revealed that hosts did not position parasitic eggs along the periphery of clutches or out of the central region more than was expected by chance, and this was the case for parasitic eggs laid both before and after the onset of incubation. Similarly, nest-level analyses showed that parasitic eggs were random in all but the smallest clutch, which contained one identified parasitic egg. Thus, parasitic eggs were not moved to the periphery of heavily parasitized clutches, where egg temperature gradients between central and peripheral regions of nests are expected to be greatest. Only four eggs (< 0.5% of 1276 eggs) were found buried within nest bowls. Eggs that were removed from nests consisted of parasite and host eggs and were more likely along the periphery of clutches prior to their removal than was expected by chance. Our results indicate that discriminatory egg incubation of parasitic eggs is not a well-developed tactic for defending against CBP in red-breasted mergansers, though hosts may rely on certain cues to decide which eggs are to be removed from nests (e.g. addled eggs).

Migratory birds are physiologically challenged by intense exercise while fasting during flights that may last hours to days. Exercise-induced oxidative stress could compromise flight performance by inducing mitochondrial dysfunction in the flight muscle. Endurance flight is partially fuelled by the catabolism of lean tissues, but how this catabolism is partitioned between different organs and muscles has not been previously studied under controlled conditions. We hypothesized that simulated migratory flight would result in dysfunction of flight muscle mitochondria, and selective catabolism of lean tissues. We predicted that simulated migratory flight would cause reduced mitochondrial oxidative phosphorylation capacity while increasing emission of reactive oxygen species (ROS) and that lean tissue mass catabolism would preferentially occur in digestive organs not needed in flight. We measured mitochondrial function, muscle morphology and the wet masses of organs and muscles following 8-hour wind tunnel flights in blackpoll warblers Setophaga striata, which use multi-day nonstop flights as part of their migration strategy. In contrast to our predictions, we found that simulated migratory flight did not alter mitochondrial fatty acid oxidation capacity or ROS emission. However, flight and fasting increased whole-animal lean mass catabolism and were associated with reductions in the masses of liver, gizzard and proventriculus, but masses of tissues in the flight apparatus (pectoralis, heart, lungs) were unaffected. Pectoralis muscle fiber morphology was also unchanged over the tested flight duration. Our findings indicate that mitochondrial function in blackpoll warblers is robust against damage induced by simulated migratory flight, and energy deprivation is sufficient for organ catabolism.

Physiological parameters have the potential to serve as valuable early warning indicators for the conservation of animal populations. However, measuring physiological adaptations in wildlife is often challenging, due to intrinsic differences causing natural variations of physiological measures between individuals across species. This study is aimed at addressing this by investigating the influence of intrinsic factors, including sex, age, body condition, and the incubation of eggs on the H/L ratio of a forest bird community. As physiological measure, we used the heterophil to lymphocyte (H/L) ratio of individuals belonging to different species in the forest bird community, which was assessed using a novel deep learning approach based on convolutional neural networks (CNNs) applied to whole blood smear scans. Using phylogenetically controlled Bayesian analyses across the bird species, we found higher H/L ratios in adult birds than in juveniles and observed slightly higher H/L ratios in females than in males. While body condition had no effect on the H/L ratio, incubating birds tended to have higher H/L ratios than non-reproductive birds, regardless of their sex. Furthermore, we found a robust phylogenetic signal of the H/L ratio in the studied bird community. Our results reveal significant general patterns of the effect of intrinsic factors on the H/L ratio across a bird community.

Anthropomorphic activities have a large impact on ecosystems in many ways, one of which is how animals behave. Non-motorised nature recreation is a popular human activity of which the impacts on nature are largely unknown. These activities, which include hiking, biking, pet walking and horseback riding, tend to increase during the commencement of the breeding activity for most passerine forest birds in temperate zones. We here investigated whether variation in recreational activity associates with patterns of nest box occupation and reproductive success in a long-term study of personality-typed great tits Parus major. We measured human disturbance in the area by recording the frequency of non-motorised recreational activities by observations. We were particularly interested in the relationship between disturbance levels and nest box occupancy as well as the relationship between disturbance levels of occupied nest boxes and exploratory scores of the great tits that occupied them. We also investigated whether reproductive characteristics such as fledging success, clutch size, chick weight and tarsus length varied with disturbance levels at occupied nest boxes. We did not find a direct association between nest box occupation and disturbance. Habitat quality rather than disturbance explained the nest occupation. Furthermore, more exploratory individuals occupied boxes in less disturbed areas, independent of habitat quality. Fitness decreased with increasing disturbance independent of habitat quality. Chicks were heavier and had longer tarsi, and clutch sizes were bigger in less disturbed areas. In conclusion, we found breeding site choice of great tits to be independent of human activity, although there are clear fitness effects of human disturbance.

Carotenoid-based plumage color is crucial in avian mate selection, often serving as an indicator of individual quality. To determine whether carotenoid-derived color can be a sign of individual condition and if there is a relationship between an individual's condition and color production, it is necessary to identify how carotenoids are acquired by individuals and subsequently used by the organism. Our objective was to determine how carotenoid pigments are used in the stripe-tailed yellow finch Sicalis citrina, a species wherein females exhibit a light yellowish ventral color while males are bright yellow. By using carbon and nitrogen stable isotope analyses we were able to determine if these carotenoid-derived colors are a signal of individual condition in terms of physiological stress and body condition. Females with low δ¹³C values (≈ −18‰) indicating the consumption of C₃ and C₄ seeds, exhibited colors shifted toward longer wavelengths and better body condition, and those with such color shifts also had higher carotenoid concentrations. In contrast, brighter females had higher δ¹⁵N values, indicating greater consumption of arthropods. Males with more saturated ventral patches had higher carotenoid concentrations, while those with colors shifted toward shorter wavelengths or lower H/L ratios, i.e. less stress, exhibited high δ¹⁵N values, suggesting that they supplement their diet with arthropods (δ¹⁵N ≈ 5‰). Our results show that the carotenoids dynamics in stripe-tailed yellow finches differ between sexes and highlight how food sources impact condition, stress, and ornamentation. Our study indicates that sexual dimorphism extends beyond plumage color to deeper physiological and ecological differences.

Incubating passerines modulate their behavior in response to local conditions and changing energetic demands, and nest microclimate can significantly influence female incubation behavior. We tested how ambient temperature affects incubation behavior, and how incubation behavior in turn influences in-nest temperature for an open-cup nesting passerine, the hooded warbler Setophaga citrina. We also examined how covariates of brown-headed cowbird Molothrus ater parasitism, clutch size, year, and females' experience influence female management of incubation behavior and in-nest temperatures. We used iButtons to measure nest microclimate and in-nest temperatures for incubating hooded warblers in southern Ohio, USA, and we used in-nest temperatures to estimate incubation behavior. Under warmer ambient conditions, females incubated for longer periods of time, with fewer (but longer) off-bouts, resulting in a higher proportion of time spent incubating. These data suggested that females under cooler circumstances leave the nest more to forage for themselves; while warmer conditions allowed females to stay on the nest longer for each on-bout, and for a greater proportion of the day. However, increasing variability of ambient temperatures caused females to take more off-bouts and on-bouts. Incubation behaviors directly influenced the realized in-nest temperatures: longer on-bouts and more incubation time overall generated higher and more stable in-nest temperatures. In contrast, longer off-bouts resulted in lower mean in-nest temperatures and less stable nest temperatures, resulting in lower hatching success. Our results linked the flexibility of incubation behavior in response to nest microclimate variation to in-nest temperatures and hatching success for an open-cup nesting species, contributing to a better understanding of how climate influences critical maternal behaviors.

Keywords: climate, incubation behavior, nest microclimate, parent–offspring conflict, reproductive rate, tradeoff