Journal of Avian Biology最新文献

Mitochondrial genome duplications, particularly within the control region, can influence evolutionary trajectories and population structure, yet their prevalence and dynamics in birds remain insufficiently understood. The rey-headed lapwing Vanellus cinereus has recently undergone a rapid range expansion in Japan, providing a unique opportunity to study genome evolution under demographic change. We combined nanopore long-read sequencing and Sanger validation to characterize complete mitogenomes of 44 V. cinereus individuals from historical and newly established populations across Japan, along with partial sequences from a congener, the northern lapwing V. vanellus. We analyzed structural variations, gene conversion events, and phylogenetic relationships to elucidate the evolutionary history of these populations. All V. cinereus individuals harbored a conserved ~ 2.5 kb tandem duplication spanning cytochrome b to the control region. The duplicated copies exhibited high similarity within individuals (mean 99.05%) with evidence of ongoing concerted evolution. We identified a ‘chimeric' individual displaying discordant phylogenetic positions between copies within single long-reads, capturing a snapshot of the incomplete homogenization process via gene conversion, rather than heteroplasmy. Phylogenomic analysis revealed a specific lineage (‘Akita–Okayama' clade) that became predominant in the recently established Okayama population (62.5%), likely due to a founder effect. This study demonstrates the utility of long-read sequencing for resolving complex mitochondrial structures. The results reveal that the mitochondrial genome of V. cinereus is shaped by the interplay of structural instability (duplication), concerted evolution, and demographic history (founder effects) during range expansion.

Recent advances in the field of wild avian microbiome research have significantly deepened our understanding of the eco-evolutionary dynamics of bird–microbe interactions. Consequently, the field is now approaching a pivotal moment in uncovering the ultimate factors shaping avian microbiome structure, especially in relation to birds' ecological, evolutionary, and dietary diversity. Yet, avian microbiome researchers face persistent methodological challenges. Based on discussions from a round table session at the 2023 European Ornithologists' Union Congress in Lund, Sweden, which brought together researchers studying host–microbe interactions across avian systems, here we highlight shared obstacles and potential solutions to strengthen the prospects of the field. This work outlines and discusses key challenges faced, and considerations to be taken into account by avian microbiome researchers throughout the scientific process, while pinpointing areas of research that need attention to advance the field. Disseminating these insights can foster innovation and collaboration, while providing a roadmap for young and new scientists who are interested in the field of avian microbiomes.

Long-distance migrants face numerous challenges during their migration, with the spring migration timing being particularly important, as early arrival at the breeding grounds often enhances breeding success. Both innate and environmental factors influence migration timing in birds, and the earlier arrival of males than females is common among songbirds breeding in temperate zones. The great reed warbler Acrocephalus arundinaceus males departed from the wintering grounds 10.5 days earlier than females. Interestingly, the oldest males (≥ 4-year-olds) departed significantly earlier than younger adult males (2- and 3-year-olds), suggesting that accumulated experience and/or age-related hormonal changes may underlie this pattern. No significant differences were observed among female age groups. In contrast, we found no significant age effect for the duration of spring migration in either males or females. Males arrived 9.9 days earlier than females at the breeding grounds. Similar to departure dates, the oldest males (≥ 4-year-olds) arrived significantly earlier than middle-aged males (3-year-olds), while no such age-dependent relationship was observed in females. In both males and females, we found positive relationships between the departure date from the wintering grounds and the arrival date at the breeding grounds with a slope of β = 0.59, showing that spring migration duration becomes shorter as the spring season progresses. In addition, for a given departure date from the wintering grounds, males arrived 3.9 days earlier than females, but no significant differences were observed between age groups either in males or females. Our findings have important implications for understanding how long-distance migratory birds might adjust their endogenous migration programs based on individual qualities, and highlight the potential role of learning and experience in these processes. This further emphasizes how adaptations to ongoing climate change might depend not only on individual quality, but also on plasticity and the age structure of the population.

Migration is thought to be costly such that challenges faced during migration likely affect how birds migrate through direct selection on migratory behavior. Survival throughout the annual cycle and conditions that affect the survival costs of migration are therefore critical to our understanding of the causes and consequences of migration. Estimating daily survival throughout the annual cycle of migratory birds has only recently become possible. We used over a decade of GPS tracking data from 186 migratory Buteo lagopus to quantify causes of mortality as well as demographic, seasonal, and spatial variation in daily survival and how survival consequences of migration changed during an outbreak of highly pathogenic avian influenza virus. The cost of migration via direct mortality varied between avian influenza and baseline study periods. Surprisingly, mortality risk during typical spring migrations was lower than in all other seasons, but mortality risk during the avian influenza outbreak was higher during both spring and fall migrations. Additionally, we found increased mortality risk in females during the avian influenza outbreak but no sex differences during baseline periods. Hence, the relative cost of migration was altered by the virus. During baseline periods, mortality risk was highest during late fall migration and winter, coinciding with increased anthropogenic-related mortalities at lower latitudes. However, the number of deaths caused by avian influenza (n = 11) in a single year equaled the total number of deaths caused by anthropogenic-related factors (n = 11; primarily collision trauma and persecution) across all 12 study years. Overall, our study highlights how added stressors such as disease outbreaks and anthropogenic factors may exacerbate existing seasonal constraints by directly increasing mortality risk.

There is increasing evidence that over-production of reactive species (RS) constitutes a significant physiological cost for migrating birds. The current view entails that RS during migration originate primarily from increased metabolic activity associated with prolonged flights and refueling. In this review, we argue that there is another substantial, yet mostly overlooked, source for RS in migrating birds: infections. Specifically, we highlight that acute and chronic infections during migration are the norm rather than the exception, and that those infections can also result in harmful RS production, either via immune system activation or via the pathogen itself. Thus, infections may impose further oxidative costs on migrating individuals in addition to those directly caused by migratory flights and refueling. Depending on the type of infection and the associated immune responses, these costs may be substantial. Therefore, both migration- and infection-related oxidative challenges should be considered when trying to explain variation in (individual) migration strategies and in coping mechanisms used to mitigate oxidative damage. We explore the ecological and evolutionary consequences of infection during migration in relation to oxidative stress. Specific research on the processes and mechanisms involved in immune-oxidative stress may lead to fundamental advances in our understanding of the ecology and evolution of migration and residency.

Avian feathers are remarkably diverse in both form and function. Coloration is among the most studied feature of feathers, but we know relatively little about melanin-based black coloration. Despite many crows (Corvus sp.) and other corvids having black feathers that appear uniform to human perception, their feather coloration could play an important role in social communication. We therefore tested whether the coloration of American crow Corvus brachyrhynchos feathers varied by age class and sex, two socially relevant variables. Using a visual modeling approach that accounts for the visual system of American crows, we measured the coloration of American crow feathers from museum specimens. We found that feather coloration varied by age class but not sex. Older individuals had feathers with different hue and more ultraviolet than younger crows. Discriminant function analyses correctly categorized individuals into age classes based on feather coloration with high classification success. The coloration of American crow feathers did not vary based on the time since the last molt and replacement, but did vary with the time since the specimen was collected. The visual modeling approach suggests that crows can discriminate among different feather regions. One region with particularly distinctive coloration properties was a facial mask, which could potentially function to minimize eye glare. Our results suggest that feather coloration in American crows (and potentially other seemingly monomorphic corvids) could reflect underlying qualities of those individuals that are important for social communication.

Flight plays a central role in the life histories of birds but is extremely energy demanding. Reproduction is also associated with high energy demands. We might thus expect to see differences in movement behaviour between individuals that breed successfully, those that breed unsuccessfully, and those that do not breed, assuming that individuals adapt their movements in response to the constraints imposed by breeding. To investigate how the flight behaviour of individuals changes over the breeding season depending on breeding success, we used GPS-tracking data of 59 territorials Bonelli's eagles Aquila fasciata, from the French population, collected between 2009 and 2023. While flight behaviours (range of movement, i.e. the spatial extent explored by individuals throughout the day, and proportion of time in flight) showed some variation resulting from breeding success, especially in females, it was less affected than we expected. However, after chicks had fledged, both male and female parents spent more time in flight than non-breeders or unsuccessful individuals. This might be explained by individuals having invested so much in breeding by the end of the breeding season that to protect their investment they increase movement to ensure the survival of their young. Such behaviour may also be necessary for successful breeders to replenish the energy reserves used to rear their chicks. These results suggest that investing in reproduction may come at a significant cost to sedentary territorial birds, impacting their flight behaviour. However, the effect of this investment may only become apparent at the end of the breeding season, due to the accumulation of costs over time.

As environmental conditions change, the ability of species to adjust their phenology is important for fitness. Advantageous adjustments are often specific to location, species, and annual cycle phase, and are particularly complex in migratory birds that must account for environmental change at vast spatio-temporal scales. Despite the heightened vulnerability of migrants, data on phenological shifts are largely unavailable for non-breeding areas. To reduce this gap, we used ringing data from 2001–2024 from Nigeria to model passage of 10 long-distance migrant species, accounting for a behavioural gradient between locally resident ‘stayer' species and ‘movers' which only occur on passage. By assessing temporal trends and environmental associations, we strove to discern effects of ‘pull factors' from goal areas and locally acting ‘push factors'. Passage varied substantially, whereby typically stayers showed early-starting and long passage, whereas movers showed late-starting, fast passage, highlighting the importance of accounting for different movement behaviour. Peak passage across species changed only slightly over time, but a few species markedly delayed post-breeding migration and advanced pre-breeding migration, consistent with possible evolutionary adjustment to climate change. Our findings only partly confirm reported wide-spread delays of post-breeding migration and advances of pre-breeding migration. Environmental associations in Nigeria were species-specific. For some species, post-breeding passage was early in years with late vegetation senescence in Europe, while pre-breeding migration occurred early in years with early green-up in Nigeria, and particularly in cool years. These associations suggest that favourable local conditions enhance earlier departure in both migration seasons, possibly due to pull factors favouring timely post-breeding arrival in Africa and pre-breeding arrival in Europe. The sensitivity of pre-breeding migration to ambient temperature requires closer investigation of migratory birds' ability to cope with warming non-breeding grounds, and warns that projected further warming could exacerbate difficulties to keep up with earlier springs on the breeding grounds.

Bird embryos develop inside eggs, which contain maternal substances that can shape offspring phenotype and fitness. Yolk fatty acids are a key energy source for the developing embryo, with omega-6 (ω-6) and omega-3 (ω-3) polyunsaturated fatty acids (PUFAs) obtained exclusively from the diet. Therefore, food availability during the breeding season is expected to influence yolk fatty acid composition and, consequently, embryo development and growth. However, the effects of dietary variation on yolk fatty acids remain unexplored in wild birds. We investigated interannual variation in yolk fatty acid composition of free-living great tits Parus major in relation to fluctuations in beech Fagus sylvatica fructification – their preferred food – across two years differing strongly in seed abundance. We hypothesized that differences in beech seed availability would alter yolk fatty acid composition between years of high and low fructification, with corresponding correlations to the fatty acid profiles of available seeds. Hence, we analyzed fatty acids from seeds of beech and two conifers (Picea abies and Pinus sylvestris), which account for most of the tree cover in the study area, and from 112 eggs collected from 107 nests over two years. Beech seeds contained higher proportions of saturated (SFA), monounsaturated (MUFA), and ω-3 PUFAs, and lower proportions of ω-6 PUFAs than conifer seeds. Correspondingly, egg yolks had more SFA, MUFA, and ω-3 PUFAs in the year of high beech abundance, and more ω-6 PUFAs in the year of low abundance. Notably, the proportion of the conifer-associated ω-6 PUFA pinolenic acid was 64.25 times higher in years of low compared to high beech fructification, suggesting marked interannual variation in yolk fatty acid composition, likely reflecting shifts in maternal diet. Future experiments need to establish causal links between diet and yolk composition and assess the fitness consequences of different seed resources for breeding females and their offspring.

Shorebirds typically spend more time fueling and refueling during migration than they spend in actual flight, and consequently their stopover ecology has important implications for fitness and conservation. We examined spatial variation and long-term changes in stopover duration of radio-tagged western sandpipers Calidris mauri over three decades on the Pacific Coast of North America. Birds were monitored during 10 periods of northward migration at four key stopover regions including: San Francisco Bay, CA; Willapa Bay/Grays Harbor, WA; Vancouver Island/Fraser River Delta, BC; and Copper River Delta, AK. We used Cormack–Jolly–Seber models to estimate the daily probability of staying at a stopover site (φ) corrected for daily detection rates (p) in relation to annual and seasonal variation. Daily probabilities of staying were then used to calculate length of stay (LOS) in days. Mean LOS decreased at stopover sites as birds progressed northward and varied from 23.1 days at San Francisco Bay to 3.6 days at the Copper River Delta. The duration of length of stay did not show a strong temporal trend by year or decade from 1992 to 2022. Effects of covariates on LOS varied by stopover site, with locally tagged birds staying 2 to 4 days longer than birds tagged farther south, females staying longer than males, and LOS being negatively correlated with mass of the bird at the time of capture with lighter birds having a longer LOS. We suggest that western sandpipers on northward migration may be limited in their ability to reduce LOS beyond the current duration over much of northern parts of the Pacific Flyway. Covariate effects demonstrate that stopover decisions of individual birds are impacted by their energy reserves, but stable lengths of stay over three decades suggest that western sandpipers may have limited flexibility to cope with environmental change in the northern part of their migration.