Journal of Avian Biology最新文献

Feathers are complex integument structures that provide birds with many functions. They are vital to a bird's survival, fundamental to their visual displays, and responsible for the evolutionary radiation of the avian class. Feathers provide a protective barrier for the body; their water repellency is a key feature. Despite hundreds of years of ornithological research, the available literature on how feathers repel water is both limited and puzzling. Most hypotheses from the early 1900s suggested uropygial gland oil provided feathers with a hydrophobic coating. Subsequent studies showed that the feather's hierarchical structure creates a porous substrate that readily repels water with or without oil. Numerous studies and methods have been published attempting to explain, quantify, and compare the water repellency of feathers. Many overlook the role of barbules and the effect of their variation, which both likely play a crucial part in water repellency. The goal of this paper is to synthesize this research to better understand what has been done, what makes sense, and more importantly, what is missing. Previous reviews on this subject are mostly over 30 years old and did not use modern methods for systematic review. Here, we performed a systematic review to capture all relevant published papers on feather water repellency. We emphasize the crucial role of barbules in feather water repellency and why their morphological variation should not be ignored. We answer the question, what do we really know about the water repellency of feathers?

Obligate brood parasitism is a peculiar behaviour found in some bird species. The costs for their hosts can be high, generating selection for active defence strategies including foreign egg and chick rejection. Only one of these two rejection strategies seems to be expressed in any given host species, which in turn selects for mimicry in parasites only at one stage of the nesting cycle. Here, I review the cues used by hosts to recognise brood parasites in the nest and the behaviours to neutralise them, as well as counteradaptations found in parasites. Furthermore, I link these adaptations with theoretical and known processes of genetic transmission of the involved mimicry traits to the offspring. I suggest that the stage at which the parasite is recognised by the host can impose selection on the mating system of the parasite and increase the likelihood of speciation. When hosts discriminate against foreign eggs, interbreeding by male and female parasites reared by different hosts may impede speciation, but not the evolution of egg mimicry if inherited through the maternal line (via the W-chromosome). When hosts discriminate against chicks, an effective mimetic phenotype requires autosomal (or Z-chromosome) inheritance to allow expression in both male and female chicks, thus favouring assortative mating in the parasites, and potentially leading to speciation. To my knowledge, this review is the first to link host defence strategies with their potential consequences for speciation in brood parasites. I suggest future steps to fill knowledge gaps in brood parasitism.

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