Journal of Avian Biology最新文献

Under the current pattern of climate change, mountain bird populations are generally shifting their ranges to higher elevations, tracking their climatic optima. Nevertheless, space limitations at high altitudes constrain mountain species' resilience to climatic change, making them particularly vulnerable. In extreme cases, the climatic niche of some species can move beyond mountaintops, ultimately driving such species to extinction. This study presents the case of the northern wheatear Oenanthe oenanthe in mainland Spain and compares its breeding distribution from 2003 to 2022. Spain, where the species mostly occupies mountain areas, represents its southernmost distribution limit in Europe. We built environmental favourability models using information from the two most recent Spanish bird atlases and a set of climatic, topographic, human activity and lithological variables to determine the factors affecting the occurrence of the species. The influence of climate compared to all other factors was obtained using variation partitioning analysis. The northern wheatear has suffered a strong reduction (67%) in occupied areas and also in favourability throughout mainland Spain (especially in the south) where climate change may have far-reaching consequences, including local extinctions. Climate explained more than 90% of the variation in the model obtained for 2022. Interestingly, the occupied areas were, on average, 100 m higher in 2022 than in 2003. If the effects of climate warming persist, the northern wheatear will likely disappear in its southernmost distribution limit, being the Sierra de las Nieves National Park population the most vulnerable in mainland Spain. For this reason, it is necessary to implement monitoring programmes for northern wheatear populations, with priority for mountain systems wherein they already occupy higher elevations, as well as further studies on other mountain species.

Most migratory birds return every year to the same breeding sites and some species show a similarly high fidelity to wintering grounds as well. Fidelity to stopover sites during migration has been much less studied and is usually found to be lower. Here, we investigate site fidelity and distance to previously visited sites throughout the annual cycle in the common cuckoo, a nocturnal trans-Saharan migrant, based on satellite-tracking data from repeated annual migrations of thirteen adult males. All birds (100%) returned to the same breeding grounds, with a median shortest distance of only 1 km from the locations in previous year. This was in strong contrast to a much lower and much less precise site fidelity at non-breeding sites during the annual cycle: In only 18% of the possible cases in all non-breeding regions combined, did the cuckoos return to within 50 km of a previously visited non-breeding site, with no significant differences among the main staging regions (Europe in autumn, Sahel in autumn, wintering in Central Africa, West Africa in spring, Europe in spring). The shortest distance to a previously visited non-breeding site differed among the staging regions with median shortest distances for the longest stopovers of 131 km [2;1223] (median [min;max]) in Europe, 207 km [1;2222] in Sahel in autumn and 110 km [0;628] in Central Africa. The distance to a previously visited staging site decreased with the time spent at the stopover in a previous year. Understanding the drivers of recurrence and site selection in migratory birds are important for guiding conservation efforts in this group but further studies are needed to establish whether the patterns observed in cuckoos are general among terrestrial migrants with continuous distribution of habitat.

Avian preen gland helps birds cope with their environment, although its overall functioning remains unclear. We shed light on the complexity of the preen gland's functioning by studying how multiple factors associate with gland morphology (size and shape) and physiology (wax secreted) in barn owls Tyto alba. Individual factors (sex, breeding stage, body condition) were more important predictors of preen gland than environmental factors (temperature, humidity, brood size). Sex, depending on breeding stage in adults, influenced preen gland traits, pointing to the preen gland's regulation by sex hormones and a greater pressure on females to protect their eggs, offspring and themselves throughout reproduction. Adults and fledglings in better condition had larger glands, pointing to the existence of physiological costs. Temperature and humidity, in interaction with plumage coloration, also influenced but to a lesser extent preen gland traits, suggesting that melanin pigmentation and preen gland act as superseding mechanisms when protecting plumage against microorganisms. Finally, fledglings living in larger broods had larger glands, suggesting a role for the social environment in preen gland's functioning. Overall, our study supports the idea that preen gland functions in diverse biological contexts within the same species and is thus subject to multiple selective pressures.

The evolution of interspecific mimicry does not always result in perfect resemblance between mimics and models. Differences between members of a mimicry complex can be explained by genetic or developmental constraints. Alternatively, imperfect mimicry might be the outcome of a tradeoff between multiple selective pressures. In this study, we explored the evolutionary conflict between mimicry and hybridization in woodpeckers. Based on the selective tradeoff hypothesis, we expected that mimicry complexes will start to evolve once the constraint of maladaptive hybridization is relaxed. Hence, we predicted limited overlap in the divergence times between hybridizing species pairs and members of a mimicry complex. This prediction was supported by clear tipping point in the probability of hybridization and mimicry at ca 9 million years of divergence. Around this timepoint, the probability of hybridization approaches zero while the probability of belonging to a mimicry complex increases. This finding is only correlational and remains to be confirmed in other taxonomic groups. Nonetheless, our results suggest a selective tradeoff between evolving interspecific mimicry and avoiding maladaptive hybridization in woodpeckers.

Multiple raptors show juvenile plumage that is substantially different from that of their parents. Here, we test the prediction that the colouration of the juvenile northern goshawk Accipiter gentilis resembling the colouration of the common buzzard Buteo buteo acts as a form of aggressive mimicry. The goshawk specialises in hunting larger birds and mammals up to the size of geese or hares, while the buzzard preys mostly on small rodents. Larger birds may thus consider juvenile goshawks as less dangerous raptors, and the juvenile goshawk may thus gain an advantage when hunting. We used the Eurasian magpie Pica pica, a common prey of the goshawk, to test this prediction. We compared the behavioural responses of magpie parents defending their freshly fledged young towards mounts of an adult goshawk, juvenile goshawk, and buzzard. To be able to assess whether this behaviour differs from responses to a nest predator and a harmless bird we also presented a common raven Corvus corax and common pheasant Phasianus colchicus as baseline stimuli. Both juvenile and adult goshawks elicited antipredatory behaviour, but magpies took more risks facing juvenile goshawks. Additionally, the intensity of antipredatory behaviour towards the juvenile goshawk was also higher than towards the buzzard. We thus conclude that magpies do distinguish between juvenile and adult goshawks, as well as they do distinguish juvenile goshawks from buzzards. They are able to assess the threat particular raptors represent and respond accordingly. Analysis of spectral reflectance of stuffed specimens of these three raptors suggests there are differences, which can be used for the appropriate recognition. In conclusion, we cannot confirm the hypothesis of aggressive mimicry in juvenile goshawks that interact with magpies.

The temperature experienced by avian embryos during development has important impacts on their growth and post-hatching phenotypes. Ambient temperature can directly affect avian nest temperature and indirectly affect it through its impact on parental incubation behaviours. Because the nests of uniparental incubators are usually left unattended more frequently than the nests of biparental incubators whose nests can be attended by another bird when one bird leaves the nest, we predict that the effect of ambient temperature on nest temperature and thus on embryonic development (specifically, incubation period length and hatching success) and post-hatching phenotype (i.e. potential carry-over effect on nestling body mass and condition) should be greater in uniparental incubators than in biparental incubators. To test this prediction, we studied two congeneric species, the biparental incubating black-throated tits Aegithalos concinnus and the uniparental incubating silver-throated tits A. glaucogularis. We found that although the embryos of the two species both developed faster (shorter incubation period length) when ambient temperature was higher, the slope was significantly greater for silver-throated tits than for black-throated tits, consistent with our prediction of a greater effect of ambient temperature on embryonic development in silver-throated tits. However, the result was not due to a greater effect of ambient temperature on nest temperature, because nest temperatures of the two species had positive relationships with ambient temperature in a similar way. Therefore, it implies a greater response of silver-throated tit embryos to temperature change. In addition, ambient temperature during the incubation stage did not affect either hatching success or nestling body mass and condition in both species. Although our predictions were not fully supported, our findings highlight the different responses of embryonic development to environmental changes between a uniparental incubator and a biparental incubator, and suggest further research to explore the mechanisms.

The Nanling Mountains, an important mountain range and watershed in south China, harbor a wealth of relictual plant species, and are considered a ‘museum' of subtropical biodiversity. With respect to birds, however, the roles of the Nanling Mountains in impeding the dispersal of the subtropical birds and, as a result, shaping their population and community structures have received little consideration. To examine these roles, we compiled and analyzed two datasets. 1) To test the mountains' influence on gene flow, we undertook a comparative phylogeographic study comparing mitochondrial COI and Cytb DNA sequences of five sylvioid resident bird species of the mountains (Huet's fulvetta Alcippe hueti, red-billed leiothrix Leiothrix lutea, greater necklaced laughingthrush Pterorhinus pectoralis, Indochinese yuhina Staphida torqueola and mountain bulbul Ixos mcclellandii). 2) To examine differential community development over the history of modern birds, we examined distributional data of all species of the Nanling region using public species occurrence records. For part 1), we sampled 327 individuals from 36 sites and conducted correlation analysis of genetic and geographic distances, taking into account the landscape of the mountains. We found that the mountains do not seriously impede gene flow among populations but influenced species differently. For part 2), comparative analysis of 446 species in 81 families indicated that family membership influenced the community composition of birds in Nanling region. Variation in family distributions is attributable to both environmental and evolutionary factors. Overall, we found that the Nanling Mountains are not currently a substantial barrier to gene flow among the species we studied but act as a corridor and refuge for these birds. However, analyses on higher ranked community data suggest the mountains acted as a barrier in older times, corresponding to the known diversification events in southeast Asian avifauna.

Global biodiversity loss is a major environmental concern. The wildlife on islands are particularly vulnerable to threats posed by alien predators, habitat loss and overexploitation. Effective conservation management of vulnerable species requires reliable information on vital population rates for all life stages and an understanding of key environmental drivers. However, demographic data are often not available for island populations before they decline or are extirpated. Here, we use Cormack–Jolly–Seber (CJS) models and 15 years of data for 1370 juveniles and 687 adults to estimate apparent survival for a genetically distinct resident population of Kentish plovers Charadrius alexandrinus on the island of Maio, Cabo Verde. We report two main findings. First, environmental conditions have a large effect on demographic performance since chicks that hatch during dry years experience a tenfold reduction in first-year survival compared to chicks that hatch during wet years. Second, female and male plovers in Maio are expected to live for 7.41 ± 0.69 (mean ± SE) years and 6.75 ± 0.64 years, respectively, due to relatively high annual survival among comparable-sized shorebirds. High adult survival thus could buffer the population against low reproductive success that this population has experienced over the last decade. Cabo Verde is typical of tropical islands with increased development that can impact native breeders and/or will accelerate habitat loss. Thus, more frequent droughts associated with climate change may exacerbate the prospects of native wildlife on many islands.