Journal of Avian Biology最新文献

Hover-feeding by hummingbirds from pendent flowers relative to horizontal flowers increases the metabolic cost of flight, but in nature a large proportion of hummingbird-pollinated flowers are nonetheless oriented near-vertically downward. We used binary-choice tests to assess behavioral preference of captive Anna's hummingbirds for these two particular floral orientations. The extent of nectar consumption from artificial flowers differed significantly over a 2-hour exposure period, with birds showing greater extraction from the horizontal configuration. We also found that time spent hovering at the feeder immediately prior to nectar extraction did not vary by feeder orientation, whereas feeding duration tended to be greater at horizontal feeders. Opportunistic measurements of wild hummingbirds were also consistent with a preference for horizontal feeders. In aggregate, these observations suggest that the increased metabolic cost of hover-feeding from pendent flowers is matched by an associated behavioral aversion, at least under the conditions examined here. However, pendent hummingbird-specialized flowers are common, suggesting that additional behavioral or ecological factors underpin evolutionary persistence of this floral presentation.

Phenological changes are one of the most well recognised responses of organisms to climate change. The ability to detect phenological change often relies on long-term datasets, which are scarce in the Southern Hemisphere. As the adaptive capacity of species is highly variable, it is important to better understand how species in the Southern Hemisphere may respond to climate change through shifts in their annual cycles. Citizen science projects, like bird nest record schemes, offer valuable long-term data, although data heterogeneity can pose challenges, affecting their use in research. To investigate the suitability of the South African nest record scheme (SANRS) for estimating phenological shifts, we conducted a preliminary exploration of shifts in lay dates in four well-represented species. Firstly, we explore the composition of nest cards for each species, specifically the proportions of single- and multi-visit cards. Secondly, we explore the accuracy of single-visit cards for estimating lay dates compared to more accurate multi-visit cards. Lastly, we compared analytical approaches to test for possible shifts in lay dates. We found little differences for lay date estimates between single and multi-visit cards and our different models showed similar patterns of lay date shifts for all species. Three of our four species (African paradise flycatcher Terpsiphone viridis, cape turtle dove Streptopelia capicola, cape wagtail Motacilla capensis and laughing dove Spilopelia senegalensis) showed a shift toward later laying over the period 1950–1999. Although only based on a limited number of species, this consistent pattern towards later lay dates contrasts with the general trends found in the Northern Hemisphere for shifts toward earlier laying. The mechanisms driving these shifts is currently unclear, but in contrast to the Northern Hemisphere, in this region rainfall rather than temperature may have a stronger influence on avian breeding phenology. Our results highlight the potential of the South African Nest Record Scheme to detect shifts in laying dates, paving the way for more extensive studies of phenological changes, and the mechanisms involved, in the under-researched region.

Same-sex sexual behaviour (SSB), encompassing actions such as courtship, pair bonding, and parenting between individuals of the same sex, has been observed across numerous taxa, including birds. Yet despite its widespread occurrence, SSB remains poorly understood, often dismissed as maladaptive or the result of errors in sex discrimination. However, instances of same-sex partnerships – persistent pair bonds between same-sex individuals – challenge these assumptions, particularly in birds, whose diverse mating systems and high level of monogamy imposes strong selective pressures on pair formation and maintenance. This review synthesises our current knowledge of same-sex partnerships in birds, addressing their evolutionary origins, adaptive benefits, and broader ecological significance. We argue that the prevalence of same-sex partnerships has likely been underestimated, hindered both by historical biases in interpretation and, especially more recently, logistical challenges in data collection. Drawing on examples from across the avian class, we explore the potential reproductive and social benefits of same-sex partnerships. By reframing these behaviours as potentially adaptive rather than anomalous, we aim to advance understanding of their evolutionary persistence and encourage more systematic research into their occurrence and implications.

Feather structure contributes greatly to a birds' ability to repel water, which is essential for thermoregulation and energy use. Water repellency of feathers has traditionally been inferred by measuring a structural index based on the distance between the feather radii and vane. A more direct method measures the contact angle of a water droplet resting on the pennaceous vane. This method is used for measuring the water repellency of various materials (e.g. textiles) and we considered it a standard against which the structural index can be validated. Despite widespread use of both techniques, their level of agreement with each other has not been systematically evaluated. Additionally, few studies have tested the direct contribution of uropygial oil to a feather's water repellency. We tested the correlation between the two methods, using feathers from two high-elevation species that are adapted to the cold and wet conditions of montane systems, Swainson's thrush Catharus ustulatus and Bicknell's thrush C. bicknelli. We also compared contact angles measured on feathers before and after removing their coating of uropygial oil. We found no correlation between the methods in either species, which suggests the structural index is not a reliable indicator of feather water repellency. Removing uropygial oil significantly reduced contact angles in both species, demonstrating a direct contribution of the oil to water repellency. The lack of agreement between the structural index and contact angle method may have occurred because the structural index infers water repellency by proxy, whereas the contact angle method more directly measures the degree to which a feather repels water. We consider the contact angle method to also be more standardizable than the structural index, although it requires more sophisticated equipment. We caution against continued use of the structural index and highlight the direct role of uropygial oil in enhancing feather water repellency.

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.