Journal of Avian Biology最新文献

As day length increases in spring, birds prepare to migrate and breed, relying on timing mechanisms shaped by selection to match their behavior and physiology to ecological conditions suitable for reproduction. As the climate changes these mechanisms will determine how successful birds will be in keeping up. In this contribution, we review studies comparing photoperiodic thresholds, endocrine profiles of testosterone and corticosterone, and gene expression during pre-breeding in seasonally sympatric migratory and resident populations of a songbird, the dark-eyed junco Junco hyemalis. Elevation of testosterone in response to GnRH served as a proxy for gonadal development, visible fat served as a proxy for migratory state, and stable isotopes in feathers and claws served as a proxy for breeding and non-breeding latitudes. Living in the same pre-breeding environment, migrants prepared to migrate by fattening and delaying gonadal development, while residents initiated gonadal development while not fattening. Within migrants, estimated latitude of origin co-varied positively with fattening and negatively with gonadal development. Together these mechanisms likely serve to match timing of migration and reproduction to the future appearance of favorable environments where breeding will occur. Differences observed in the wild persisted in a common environment, suggesting genetic divergence and local adaptation, though the possibility of early developmental effects on timing remain. As the climate warms and resources to support reproduction appear earlier, locally adapted dispersing immigrants from lower latitudes may bring along their earlier timing thus providing genetic or developmental rescue. Future research on mechanisms responsible for variation in timing among populations will allow better predictions of how adaptation to climate change will unfold.

Keywords: common garden, dark-eyed junco, gonad, hormone, local adaptation, migration, phenology, photoperiodic threshold, stable isotope

Ecologically relevant factors such as exercise and diet quality can directly influence how multifaceted physiological systems work; however, little is known about how such factors directly and interactively affect key components of the antioxidant system in multiple tissues of migratory songbirds. We tested 3 main hypotheses across three tissues in European starlings fed diets with more or less antioxidants (anthocyanins) and long-chain omega-6 polyunsaturated fats (18:2n6) while being flight-trained in a wind tunnel. Stimulatory effect of flight: flight-training stimulated the antioxidant system in that 1) plasma oxidative damage (dROMs) was reduced during a given acute flight, and contrary to our predictions, 2) antioxidant capacity (OXY or ORAC) and oxidative damage in plasma (dROMs), flight-muscle, and liver (LPO) of flight-trained birds were similar to that of untrained birds (i.e. not flown in a wind tunnel). Flight-trained birds that expended more energy per unit time (kJ min⁻¹) during their longest, final flight decreased antioxidant capacity (OXY) the most during the final flight. Dietary fat quality effect: contrary to our predictions, dietary 18:2n-6 did not influence oxidative status even after flight training. Dietary antioxidant effect: flight-trained birds supplemented with dietary anthocyanins did not have higher antioxidant capacity in plasma (OXY), or liver and flight-muscle (ORAC) compared to untrained birds. Counterintuitively, oxidative damage (dROMs) was higher in flight-trained supplemented birds compared to unsupplemented birds after an acute flight. In sum, the antioxidant system of songbirds flexibly responded to changes in availability of dietary antioxidants as well as increased flight time and effort, and such condition-dependent, individual-level, tissue-specific responses to the oxidative costs of long-duration flights apparently requires recovery periods for maintaining oxidative balance during migration.

Wolverton, H. and Anderson, R. C. 2024. Syntax in animal communication: its study in songbirds and other taxa. J. Avian Biol. 2024: e03258. https://doi.org/10.1111/jav.03258.

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Houses around the world are built with a variety of materials like timber and brick, depending on a number of factors such as local climate and material availability. Similarly, non-human animals such as birds use diverse materials to build nests. Very little is known about how animals choose nest materials, and how these choices, in turn, affect the function of the nests they build. As an initial attempt to address this question, we investigated the causes and consequences of nest-material use by Dartford warblers Sylvia undata. The warblers breeding in England show considerable variation in nest materials: some nests are made almost entirely of heather, while others contain a lot of grass. We found that warbler use of nest materials were explained by the composition of the local habitats, but no evidence for relationships between nest-material composition and insulation capacity or the breeding performance. Warblers appear to be able to build equally functional nests using whatever materials are readily available in respective habitats. Studying nest-building behaviour of individual species like Dartford warblers could inform how the use of diverse material in animal architecture evolved.

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.