Ibis最新文献

Protected areas are one of the major tools used in the conservation of biodiversity, but animals are unlikely always to remain within these human-made boundaries. Understanding when and why species choose to leave protected areas can help us to improve the effectiveness of these management tools. Here, we investigate the use of protected and non-protected areas by two migratory species undergoing rapid wintering population changes in northwest Europe: Whooper Swans Cygnus cygnus and Bewick's Swans Cygnus columbianus bewickii. Global positioning system tags were fitted to 15 Whooper Swans in winter 2008/09 and to 18 Bewick's Swans from winter 2013/14 to 2014/15 at the Ouse Washes Special Protection Area (an internationally important roost for wintering waterbirds) and on adjacent fields in southeast England. Here, swans feed on farmland during the day but return to designated reserves to roost at night, where they receive protection from predators and disturbance within managed roost habitats. When swans roost elsewhere at alternative sites, they may face more adverse conditions, and so understanding the extent and causes of the use of alternative roosts is important for swan conservation efforts. The alternative roosting proportion, defined as the proportion of nights spent outside protected reserves, was 0.237 for Bewick's Swans and challenging to quantify accurately for Whooper Swans. A generalized additive mixed model to model repeated measurements on individuals showed that the proportion of time that Bewick's Swans spent at alternative roosts correlated positively with river level and negatively with temperature. Competition and foraging flight distances are thought to drive these relationships, as swans seek access both to roost space and to nearby feeding habitats. Our findings improve our understanding of the environmental conditions under which migratory waterbirds may choose to roost outside protected areas.

For animals which exploit predictable food resources, greater foraging site fidelity has been hypothesized to lead to increased foraging efficiency. However, evidence for this in free-ranging species is limited. In the present study, foraging site fidelity, the factors influencing it and its effect on foraging effort were investigated in the Black-faced Cormorant Phalacrocorax fuscescens, a predominantly benthic forager occurring in southeastern Australia. While the study population was found to have a relatively large foraging range, individuals were highly consistent in the smaller foraging areas which they used. Foraging effort was lower in individuals with a higher foraging site fidelity, which is likely to indicate increased foraging efficiency. Foraging site fidelity differed greatly between individuals but none of the assessed factors (sex, mass, size or year of study) were found to have a significant influence. This might indicate that intrinsic factors which could not be assessed, such as personality or experience, may influence the degree to which individuals exploit known habitats. The findings suggest that changes in prey availability or distribution could result in reduced foraging efficiency and, consequently, negative impacts for the species. Further investigation is required to assess within-individual foraging plasticity to predict potential responses to changing prey availability and distribution.

The COVID-19 pandemic, which significantly altered human activities, particularly in urban areas, presented a unique opportunity to explore the dynamics of wildlife–human coexistence. In this study, we conducted bird counts in 36 parks in Poznań, Poland, before (2019) and during (2020) the pandemic lockdown, and assessed the impact of lockdown-induced changes in human activity on the presence of birds with different diet type in the city. We found a notable decrease in the occurrence of granivorous and waste-feeding birds in urban areas during the pandemic, but the presence of birds feeding mainly on other food sources remained relatively unchanged. This study provides initial evidence of a cross-species and diet type-related decline in bird diversity in urban parks during the COVID-19 pandemic.

Landfills provide an abundant and predictable food source for avifauna. The energy and time that are saved because of landfill-foraging have had positive effects on the distribution of bird breeding populations and their reproductive parameters. However, the proliferation of individuals coinciding with the appearance of landfills often increases human–wildlife conflicts and intensifies the contact between waste and the environment. In this context, a landfill in Madrid (Spain) implemented deterrent measures in 2021 aiming to reduce the influx of birds inside its facilities. This study aims to describe the effects that a reduction in the accessibility and availability of landfill food resources may have had on the surrounding breeding populations of White Stork Ciconia ciconia. For this purpose, the breeding parameters of three populations with different landfill use indices were analysed before and after the application of bird deterrent measures. The closest population, with the highest landfill use index, suffered a drastic reduction in fledgling productivity during the breeding season with bird deterrent measures. On the other hand, a drought during one of the breeding seasons negatively affected the productivity of the populations that relied partially and completely on natural food resources (located at medium and long distance from the landfill, respectively). Landfill-foraging might have mitigated the consequences of the natural food scarcity caused by this drought, even with the application of bird deterrent measures. Overall, our results show the potential negative impact of bird deterrent measures on populations dependent on landfill food, and highlight the importance of assessing the effect of these techniques beyond the site to determine their appropriateness. Due to the imminent closure of landfills and the expected worsening consequences of climate change, monitoring programmes should be established to determine the long-term effects of bird deterrent measures and unusual environmental conditions on White Stork populations.

Many wildlife species consume food or refuse provided by humans. To understand the effect of anthropogenic food subsidies on wildlife populations, we first need to quantify where and when individuals can access such food sources. The Red Kite Milvus milvus is an opportunistic raptor species and uses both inadvertent and deliberate food subsidies provided by citizens. Here we present a new approach using global positioning system (GPS)-tracking data to predict where anthropogenic food subsidies probably occur. We tracked 497 individuals with solar-powered GPS transmitters over an average of 3.2 (range 1–9) breeding seasons in Switzerland, and combined these data with locations of 125 known feeding sites obtained through interviews. We used two sequential random forest models, at both individual movement and population levels, to predict where anthropogenic food subsidies were attended by Red Kites. The first model classified locations that were frequently and regularly revisited, and successfully predicted 85% of locations that were within 50 m of an externally validated feeding site. These predicted locations were aggregated in 500-m grid cells to calculate the proportion of individuals and locations associated with predicted food subsidy. A second model related the presence of known food subsidies to the aggregated predictions. In our study area, 80% of known anthropogenic food provision locations could be correctly identified using Red Kite tracking data, but data sparsity beyond the core range of tracked individuals limits predictions of anthropogenic food subsidies at larger geographical scales. Nonetheless, biologging data can identify ephemeral food sources, and facilitate an assessment of the importance of anthropogenic food subsidies for the fitness of individuals in tracked populations.

For long-lived species, adult survival is the parameter that theoretically has the strongest impact on population dynamics; this makes its estimate crucial for conservation management. The use of non-invasive genetic approaches coupled with capture–recapture methods is being used increasingly to estimate adult survival. Despite being regularly employed in mammals, it has been little-used in birds and notably in long-lived territorial species. This study aimed to determine if feathers obtained from eagle nests could be used to estimate the adult apparent survival rate and the costs associated with such an approach. Feather samples (n = 180) were collected in nests (n = 78) and directly from individual Golden Eagles (n = 36) Aquila chrysaetos in France and were genotyped using 17 microsatellite markers. The genotyping error rates obtained were low, with 3% amplification failures, 3.1% dropouts and 1.7% false alleles. The genetic variability of the markers was high, with a probability of identity between siblings of 6.8 × 10⁻⁶, allowing reliable individual identification. Of the feathers collected in nests, 90% were from breeding females; this allowed apparent survival to be estimated for adult females at a reasonable cost. The genotyping of three feathers collected from a nest ensured individual identification of the breeding female with near certainty. Our simulations showed that monitoring of at least 20 pairs over 5 years, or 10 pairs over 10 years is necessary to detect a 10% absolute decrease in adult apparent survival. Estimating the adult survival rate of long-lived birds using feathers collected in nests is possible. A substantial budget, albeit one that is likely to be lower than that for a common capture–recapture survey, would be needed to obtain precise survival estimates.

Avian begging calls mediate parent–offspring conflict and direct parental care to genetically related progeny. We found that the fundamental frequency of begging calls of African Penguins Spheniscus demersus decreases as the penguins age and gain mass, before reaching a lower plateau when the chick reaches about 1 kg. Our results suggest that the food solicitation signals of this species may inform parents of the offspring's body mass. Our results may also lead to the development of non-invasive tools for facilitating censusing chick growth in wild colonies.

Vegetation structural complexity surrounding nests can either provide concealment for intruders and mates or make it more difficult for hosts to recognize parasitic eggs. We investigated whether shading and vegetation aggregation increase extrapair paternity (the presence of broods with half-siblings) and intraspecific brood parasitism (IBP, the occurrence of broods with unrelated offspring) in socially monogamous Blue-black Grassquits Volatinia jacarina. We found that habitat shadowing was associated with increased occurrence of IBP, but found no association between the degree of shade and the presence of extrapair offspring. Our findings support the idea that habitat limits cryptic reproductive behaviours and that female grassquits may benefit from habitat shadows to parasitize conspecific nests.

Wide variation in visual field configuration has been recorded among avian species and it is hypothesized that this variation is driven primarily by foraging ecology and predator detection. It has also been shown that visual field configurations can render some species more vulnerable to collisions with human artefacts that extend into open airspace, such as power lines and wind turbines. Visual fields have three main components: the monocular fields describe the extent of the world seen by each eye, the binocular field describes the region where the monocular fields overlap, and the blind area describes the region in which no vision is provided. Among birds, the topography of the binocular field, and the extent and position of the blind area, show considerable interspecific variation. Although Laridae (gulls, terns, skimmers) are a large and cosmopolitan taxon, visual field characteristics of only one species, Black Skimmer Rynchops niger, have been determined. However, skimmers are distinct from other Laridae species because they use a specialized foraging technique based upon tactile cues. We determined visual fields in three species of gulls (European Herring Gulls Larus argentatus, Lesser Black-backed Gulls Larus fuscus, Black-legged Kittiwakes Rissa tridactyla), and found that they show the key characteristics associated with visually guided foraging. However, the binocular field does not extend through the full height of the frontal field. This results in a blind sector, which can project in the direction of flight when gulls pitch their heads sufficiently far forwards to visually search the surface below. This could render gulls vulnerable to collisions with anthropogenic structures (power lines, wind turbines) that extend into the open airspace. Photographs show that gulls in level flight do pitch their heads forward sufficiently to render them almost blind in the direction of travel, and further work on the head positions adopted by gulls in flight are recommended. The visual field of skimmers differs markedly from those of gulls. Their binocular field topography is interpreted as functioning in the control of bill position when skimming (flying just above the water surface with the elongated, blade-like, rhamphotheca of the mandible extending through the water surface). Skimmers also have a blind area, which projects forwards in the direction of travel when skimming. This can be associated with the vulnerability of skimmers to collisions with objects that extend just above the water surface.