Journal of Avian Biology最新文献

Heavy metal pollution is known to negatively affect numerous traits in birds, including foraging, metabolism, immunity, and reproductive success. In this study, our primary aim was to assess the impact of metal pollution exposure on the visual appearance of the pied flycatcher Ficedula hypoleuca eggs. Specifically, we focused on blue-green biliverdin-based coloration, a trait expected to function as a signal of female quality to males. In line with the sexually selected egg coloration (SSEC) hypothesis, which posits that males respond to more intensely colored eggs by increasing their provisioning effort, our second objective was to investigate whether metal pollution exposure affects this specific signaling mechanism and subsequent male behavior. Our results showed that although coloration did not correlate with female quality or male provisioning effort, egg blue-green coloration decreased in polluted areas compared to non-polluted control areas. Our analysis of reflectance data revealed that this difference was due to an increased ultraviolet reflectance of eggs from polluted areas, likely caused by changes in eggshell microstructure (e.g. porosity). We therefore propose that metal pollution exposure may compromise crucial color signals of bird eggs. Avian visual modeling indicated that eggs laid by different flycatcher females are generally very similar, making discrimination by males challenging and perhaps impossible especially in dark cavities. Overall, our results suggest that the SSEC hypothesis may lack adaptive relevance for the pied flycatcher in northern Europe, even in environments influenced by anthropogenic activities.

This article provides insight into the trophic strategy of a little-known top predator and allows for a better understanding of the selective pressures that shape its diet. We studied the diet of European honey-buzzards, a raptor specialized in consuming social wasp brood. The ratio of predator to prey biomasses is one of the highest among raptors. Considering the prey size and ingestion rate hypothesis, we investigated the honey-buzzard's preferences for native and exotic eusocial vespid species. We also described other prey items in the diet and how diet changes throughout the breeding season. We installed trail cameras in 24 honey-buzzard nests in north-western Spain in 2018–2021. We estimated the proportion and daily rate of delivery of native common-wasps, invasive Asian-hornets, reptiles, and birds and the honey-buzzard's preferences for vespid species. We performed LMMs, GLMMs, and CLMMs to analyse relationships between response variables and predictors. Honey-buzzards mainly consumed vespids (82% of prey). Common-wasps and Asian-hornets were almost the only two vespids consumed. The invasive hornet was the second most consumed prey, but common-wasps were preferred. Vespids became more important as the age and number of nestlings increased. Our results suggest that this diet is the adaptive result of the conflict between being a median-sized insect-eating nidicolous raptor and collecting enough morsels for the growth of its nestlings. This would allow them to deliver a relatively large amount of biomass to the nest with a high ingestion rate. We discussed implications of our findings for the management of the invasive wasp.

Animal migration is a fascinating phenomenon that has puzzled mankind since the time of ancient Greece. It is a process widespread across a varied range of taxa and it shines especially in birds which, because of their mobility, display an amazing diversity of routes and strategies. With the advances in tracking devices and improvements of sequencing technologies, recent work provides support for a strong genetic influence of several migratory traits across different species. However, there is little to no evidence of any common sequence-based mechanism behind this complex behaviour, nor any unifying principle explaining it. We review how the focus in understanding the genetic basis for migratory traits should be shifted towards studying regulatory mechanisms of gene expression instead of the traditional candidate gene approach. Importantly, a role for gene expression as the underlying driver of the migratory phenotype can resolve the opposing and often strong views that migration is mainly either under genetic or environmental influence. We emphasise that research should take new directions, reinforcing that there is probably not a common genetic basis for how migration is regulated in birds. Here, we support the notion that 1) migration can only evolve this fast if it is a quantitative trait with a large standing variation; 2) the main drivers for migration evolution seem to be diverse expression–regulation mechanisms rather than gene-level polymorphisms; and 3) non-coding sequences of the genome, epigenetics and structural variation might be more important in shaping complex traits than previously thought. Further, we present several hypotheses outlining how these regulatory mechanisms might work across different bird species defining certain migratory traits.

Bio-logging has revealed much about high-latitude seabird migratory strategies, but migratory behaviour in tropical species may differ, with implications for understanding nutrient deposition. Here we use combined light-level and saltwater immersion loggers to study the year-round movement behaviour of adult red-footed boobies Sula sula rubripes from the Chagos Archipelago, tropical Indian Ocean, to assess migratory movements and estimate nutrient deposition rates based on the number of days they spent ashore. Light levels suggest that red-footed boobies are resident in the Chagos Archipelago year-round, although there are large latitudinal errors this close to the equator. Immersion data also indicate residency with tracked birds returning to land every one or two days. Spending an average of 79.86 ± 2.80 days and 280.84 ± 2.64 nights per year on land allows us to estimate that the 21 670 pairs of red-footed boobies deposit 37.34 ± 0.56 tonnes year⁻¹ of guano-derived nitrogen throughout the archipelago. Our findings have implications for tropical seabird conservation and phylogenetics, as well as for assessing the impact of seabird nutrients on coral reef ecosystems.

In numerous animals, dramatic coloration (e.g. bright red or yellow) often indicates potential fitness, but it is less clear whether subtle coloration in the same individuals (e.g. grey or brown) could also encode such signals. To determine if subtle coloration could indicate health in a bird species with colorful feathers, house finches (Haemorhous mexicanus), we used spectrometry to objectively quantify leg brightness and saturation before, six days after, and 13 days after captive individuals were inoculated with a naturally-occurring bacterial pathogen, Mycoplasma gallisepticum. We found that legs became less bright six days after infection (near the typical peak of infection), then more bright and less saturated at 13 days (entering the typical recovery period). These results suggest that subtle colors could reliably indicate current infection status, and therefore survival potential.

Mobbing is a widespread, vocally coordinated behaviour where species approach and harass a threat. The noisy miner (Manorina melanocephala) is a notorious native Australian honeyeater, well-known for its hyperaggressive mobbing. Numerous studies have identified negative impacts of their mobbing behaviour, highlighting the exclusion of competitors from colony areas and the resulting loss of woodland-bird biodiversity. Despite this, few studies have investigated mobbing itself, and our understanding of the factors which influence its expression remains limited. Here, we use a field-based playback experiment to investigate whether mobbing responses vary in relation to colony borders and caller familiarity. Noisy miners were more likely to respond, reacted more quickly and responded more strongly to mobbing calls broadcast inside as opposed to outside the colony. These behavioural differences likely arise from variation in the relative costs and benefits of responding. When noisy miners did mob outside the colony, more individuals joined in response to unfamiliar as opposed to familiar callers. Our results reveal that noisy miner mobbing may not be as indiscriminate as often assumed, with caller familiarity and location influencing this behaviour. We suggest there are benefits to greater consideration of the factors impacting noisy miner mobbing behaviour.

Keywords: Avian biodiversity, interspecific aggression, mobbing behaviour, noisy miner, vocal communication

Ecological and social factors shape individual reproductive strategies. Climate change has wide-ranging effects on the timing of reproduction and availability of nesting sites for many birds. Ecological factors such as season length or predation rate could in turn affect the relative success rates of alternative reproductive tactics (ARTs). A new article by Pöysä (2024) featuring a long-term study of common goldeneyes Bucephala clangula highlights the role of climate change in altering rates of conspecific brood parasitism (CBP) by affecting nest initiation dates and season length. While some authors have emphasized the effects of spatial and temporal aggregation of nests in promoting tactics of reproductive interference, few studies have addressed the effects of environmental variables on rates of CBP and other ARTs. I review some of the evidence for a relationship between population-level nest predation rate and rates of CBP, principally in ducks and rails, and suggest a role for high rates of nest loss from all sources in the evolution of CBP and host responses. There is a need for further studies that examine environmental correlates of ARTs. Long-term studies have the highest potential to reveal how shifts in phenology and life history variables may respond to environmental perturbations. Comparative studies of similar species in remote geographic locations can add perspective of how different ecological variables affect the prevalence of ARTs.

Farmland habitats witness steep declines in biodiversity. One rapidly declining farmland species is the ortolan bunting Emberiza hortulana. In Finland, a staggering 99% of the population has been lost during the past 30 years. Changes in the breeding habitats have been proposed as a reason for the decline, although hazards during migration and wintering may also play a role.

We gathered a 19-year data set of Finnish ortolan buntings and studied which spatial characteristics, habitat features, and climate factors might explain the population growth rate at the singing-group level. As explanatory variables we used region, density of small-scale structures, proportion of agricultural area in the landscape, diversity of crop types, proportion of bare ground, and temperature and precipitation of previous breeding season.

Higher population growth rates were associated with higher crop type diversity and higher proportion of bare ground. The mosaic of various crop plants and bare ground may provide a wider array of feeding, hiding and nesting places, and an easier access to food. Higher growth rates were also associated with landscapes dominated by interconnected agricultural land, which may reflect the species' sociability and avoidance of forested areas. The North Ostrobothnia region had higher growth rates compared to other regions.

We suggest that northern populations of ortolan bunting should be targeted for further studies on feeding and breeding ecology as well as for urgent conservation actions, such as increasing crop type diversity and bare ground.

Some taxa of wading birds can locate buried prey by detecting vibratory cues in their foraging substrates while probe-foraging, using a sensory modality called ‘remote-touch'. As more saturated substrates transmit vibrations better, we predict that these birds can detect prey in wetter substrates more easily. We used sensory assays to test whether substrate water content affects the remote-touch foraging success rate of Hadeda ibises, Bostrychia hagedash. The birds were more successful at locating prey using vibratory cues than when relying on random direct contact with the beak alone. Their remote-touch foraging success rate was positively affected by increasing water contents of the soil, but water content had no effect on their direct contact foraging success (indicating this is not an artefact of ease of probing). This may partially explain the link between the range expansion of this species in southern Africa and increased soil irrigation, as it is easier for the birds to detect prey in wetter substrates. Thus, it is likely that the distribution of other remote-touch foraging birds is affected by substrate water content, and as many of these species are endangered and rely on sensitive wetland habitats, it is vital to understand their sensory requirements for foraging.

Alarm signals have evolved to communicate imminent threats to conspecifics but animals may also perceive other species' alarm displays to obtain adaptive information. In birds, mixed-species foraging flocks are often structured around a focal sentinel species, which produces reliable alarm calls that inform eavesdropping non-sentinel heterospecifics about predation risk. Ongoing work has revealed that several species can recognize the alarm calls of certain sentinel species even without prior encounters, including when these are from distant biogeographic regions. Similar work has yet to examine whether naive subjects' responses to unfamiliar sentinel alarm calls differ from responses to non-sentinel alarm calls. Here we played the alarm calls of three subtropical Asian bird species that participate in mixed species flocks, to temperate North American birds. Birds responded most to the alarm call of an allopatric core sentinel and a local sympatric sentinel control species, less so to an allopatric non-core sentinel, and least so to an allopatric non-sentinel and a negative control stimulus. These patterns provide evidence that broad phylogenetic and geographic recognition is a pertinent aspect of sentinel alarm calls in general.