Ornithology

Are there differences in point count results between the first six hours after sunrise in subtropical forest bird communities? Abstract We compared species richness, abundance and composition of bird communities during each of the first 6 h after dawn in two types of forests in Entre Ríos, Argentina, in four seasons of 2016. Richness in each of the 6 h was similar. Additionally, richness, abundance and composition of bird communities in summer, autumn and spring were similar between the last 2 h and at least 3 of the first 4 h after dawn. We recommend counting birds in subtropical forests during the first 6 h after dawn, except in winter, when a marked drop in abundance occurs in the course of the morning.

Dispersal of fern spores by Galápagos finches Abstract Fern sporangia may provide an important source of energy for bird species, which in turn can act as potential dispersers of viable spores. This study reports the first case of fern spore dispersal by land birds. We document the consumption of fern sporangia and evaluate the potential spore dispersal by Galápagos finches on Santa Cruz Island. Overall, 18% of the 34 sampled individuals of three finch species, the Vegetarian Finch (Platyspiza crassirostris), the Small Ground Finch (Geospiza fuliginosa) and the Medium Ground Finch (Geospiza fortis), were found to disperse viable spores of two native ferns, Asplenium auritum and Asplenium feei.

Late Pleistocene climate change shapes population divergence of an Atlantic Forest passerine: a model-based phylogeographic hypothesis test Abstract Several evolutionary processes seem to have influenced the Atlantic Forest (AF) biogeographic history, as suggested by phylogeographic studies that have shown a multitude of patterns. Here, we use approximate Bayesian computation to test alternative historical hypotheses to investigate the phylogeographic pattern, historical demography, and palaeodistribution of the Grey-hooded Flycatcher Mionectes rufiventris, an endemic AF bird, distributed mainly in southern areas of the biome. Our goal was to integrate molecular and ecological data to test diversification hypotheses available for the AF. Our investigation revealed two mitochondrial phylogroups, geographically structured around the Doce River. Coalescence analyses revealed that these groups shared a common ancestor in the Late Pleistocene, between 200,000 and 300,000 years ago, and that divergence was probably associated with climatic fluctuations during this period. Demographic analyses suggested recent demographic expansion in both groups. Ecological niche modelling suggested larger ranges during the Last Glacial Maximum (LGM) than in the present, not in agreement with the genetic pattern recovered. We simulated alternative historical models to test these competing scenarios. Our findings support the existence of small populations during the LGM which expanded afterwards from putative refuges. Thus, these results suggest that the Pleistocene climate shaped patterns of diversification and demographic history of this species in accordance with the classical forest refuge hypothesis.

Multi-scale habitat requirements of forest bird species in a highly fragmented landscape Abstract Land use changes in Europe have resulted in forest loss and fragmentation that have been proved to be key factors driving the decline of various forest bird populations. Quantifying the environmental factors which allow the persistence of forest birds in highly modified landscapes is therefore essential to enhance conservation efforts. In the present study, we defined the environmental factors determining the distribution of seven forest birds (Picus viridis, Dendrocopos major, Dryobates minor, Garrulus glandarius, Poecile palustris, Sitta europea, Aegithalos caudatus) in a central portion of the Po Plain, northern Italy. In the study area, less than 12% of the whole territory is covered by broad-leaved forests (concentrated along the main rivers) and tree plantations. To obtain a full picture of the habitat requirements of these seven forest bird species, we first conducted a survey of their populations using the point count method during the 2015 breeding season, following which, using resource selection functions, we investigated the effect of environmental variables on each species, mainly focusing on the role of natural forests and tree plantations. The effect of variables was assessed both at a home-range scale and at four different scales in the surrounding context. Tree plantations, in addition to natural forests, proved to be important for most of the seven species studied, including forest specialists such as Dryobates minor and Poecile palustris. The distribution of forest species was better explained by habitat amount than by habitat configuration, both at the home-range scale and in the surrounding context. As expected, Sitta europaea was the most sensitive species to land use changes, and broad-leaved natural forests were essential for its persistence in the landscape.

Characterization of the genetic diversity and population structure of the manakin genus Antilophia through the development and analysis of microsatellite markers Abstract The two species of the genus Antilophia, Antilophia bokermanni and Antilophia galeata, are found in environments that are undergoing extensive modification, which may be provoking the loss of their genetic diversity. Nine polymorphic microsatellite loci were characterized and analyzed in each of these species. The distribution of allele frequencies revealed two clusters that reflected the distinct genetic profile of each species. Observed levels of heterozygosity were low for each species, with the lowest allelic diversity found in the critically endangered A. bokermanni. The set of loci described here, in contrast with other genetic markers that have been analyzed previously, effectively diagnosed the genetic diversity of different populations of the two species.

Mobbing of the top predator: a correlation between avian community richness and the number of mobbing species Abstract Mobbing is an anti-predator strategy initiated by one or more members of prey species aiming at driving away a predator that is not undertaking an attack. Because of a continuous dispute as to whether mobbing of a top predator may indicate species richness, we tested the correlation between the number of species engaging in mobbing and avian community richness. In the boreal forest of central Norway, we conducted a series of 83 bird census trials in 2014 and 2015. Each census trial consisted of two 5-min phases. In the first phase an ordinary point count was performed as a control; in the immediately following second phase either a stuffed Eagle Owl or Capercaillie female decoy was presented to study mobbing of a top avian predator and non-predatory species. Mobbing was more likely to occur, and the number of species that engaged in mobbing was higher, in habitats richer of bird species. Our study showed that the cumulative effects of being mobbed increase with richness of the local avian community. We did not find any support for the notion that mobbing is triggered by mobbing activity of the two most active and abundant species. No support was provided for an assertion that using an owl decoy would result in higher number of detected species during a census. Our study urges the need for identification and quantification of costs of mobbing for an avian predator.

A physiological perspective on the ecology and evolution of partial migration Abstract Billions of animals migrate between breeding and non-breeding areas worldwide. Partial migration, where both migrants and residents coexist within a population, occurs in most animal taxa, including fish, insects, birds and mammals. Partial migration has been hypothesised to be the most common form of migration and to be an evolutionary precursor to full migration. Despite extensive theoretical models about partial migration and its potential to provide insight into the ecology and evolution of migration, the physiological mechanisms that shape partial migration remain poorly understood. Here, we review current knowledge on how physiological processes mediate the causes and consequences of avian partial migration, and how they may help us understand why some individuals migrate and others remain resident. When information from birds is missing, we highlight examples from other taxa. In particular, we focus on temperature regulation, metabolic rate, immune function, oxidative stress, telomeres, and neuroendocrine and endocrine systems. We argue that these traits provide physiological pathways that regulate the ecological and behavioural causes and/or consequences of partial migration, and may provide insight into the mechanistic basis of wintering decisions. They may, thus, also help us to explain why individuals switch strategies among winters. We also highlight current gaps in our knowledge and suggest promising future research opportunities. A deeper understanding of the physiological mechanisms mediating the causes and consequences of partial migration will not only provide novel insights into the ecology and evolution of migration in general, but will also be vital to precisely modelling population trends and predicting range shifts under global change.

Responses of breeding waders to restoration of grouse management on a moor in South-West Scotland Abstract Worldwide, many wader species have recently exhibited steep declines in range and abundance. Low productivity, frequently associated with predation, is considered a major proximate driver of declines and often reflects underlying land use and habitat change. We hypothesised that restoration of grouse moor management, which includes control of predators and heather habitat management, would halt and reverse these declines. We monitored changes in the abundance of four upland-breeding wader species following restoration of grouse moor management at Langholm Moor in South-west Scotland from 2008 to 2017. Here, Curlew, Golden Plover and Lapwing had previously declined when management ceased, whereas Snipe had increased. During the 10-year study period, Curlew numbers increased on average by 10% per annum, Golden Plover numbers by 16% and Snipe numbers by 21%, whereas Lapwing numbers did not change. These local trends contrast with national and regional trends over the same period, which all showed declines of all these species. However, the population trends for Curlew and Snipe did not differ in relation to habitat management for Red Grouse, suggesting that population increases were primarily associated with predator control across the whole study area. Our results support the hypothesis that restoring predator control as part of grouse moor management can reverse declines of some wader species. At Langholm, full recovery to levels observed prior to management cessation may have been constrained by delayed recruitment within a time-restricted study period in combination with low initial numbers, availability and isolation of suitable habitat, and incomplete predator removal.

Stopover departure behavior and flight orientation of spring-migrant Yellow-rumped Warblers ( Setophaga coronata ) experimentally exposed to methylmercury Abstract Mercury (Hg) is a global pollutant that has wide-ranging impacts on the physiological systems of birds, but almost nothing is known about how this affects migration. We manipulated methylmercury (MeHg) burdens of 24 wild-caught Yellow-rumped Warblers (Setophaga coronata) before releasing them and tracking their spring migration with automated radiotelemetry to study the effect of MeHg on stopover departure behavior and flight orientation. Dosing half the birds for 14 days prior to release resulted in environmentally relevant mean blood total Hg (THg) concentrations of 6.61 (± 0.16) p.p.m., while a group of 12 controls had nearly undetectable blood THg. We observed starkly different departure behavior between groups, with dosed birds leaving the release site significantly sooner than controls. Among birds that were detected beyond the release site, seven (three dosed, four control) initially made a landscape-scale relocation before a longer-distance migratory flight, while two (controls) migrated directly from the release site. All flights were in the seasonally appropriate direction regardless of group. Rapid departures by dosed birds could have been the result of hyperactivity that can be induced by MeHg, or due to decreased social dominance that caused them to seek areas with less resource competition. We found no evidence that MeHg impaired orientation, although sample sizes were small and we had less ability to detect birds flying in “incorrect” than northward directions. The dramatic difference in departure decisions between groups indicates a potential effect of MeHg on the neurological and/or physiological mechanisms that control migratory behaviors of birds.

Pre-laying movements of Yelkouan Shearwaters ( Puffinus yelkouan ) in the Central Mediterranean Abstract The pre-laying exodus (PLE) is considered a crucial period in the breeding biology of Procellariiformes as it determines the success of egg production within a season and, therefore, a population’s reproductive output. However, it has scarcely been studied compared to other stages of the annual cycle. Here we present the first pre-laying tracks of the vulnerable Yelkouan Shearwater (Puffinus yelkouan) through the Global Positioning System tracking of birds breeding on the Maltese islands in the Central Mediterranean, and compare PLE core utilisation areas to known areas used during the chick-rearing period. Females spend, on average, 13 days foraging during egg development, reaching an average maximum distance of 325.5 km from their breeding colony to forage at offshore areas mainly south of the Maltese islands; these journeys are of longer duration and cover a greater distance than those undertaken by males, and by females that are not developing an egg, during the same period. There is little to no overlap between the PLE core utilisation areas and those used during chick-rearing by the same populations. This confirms our expectations that the PLE differs from foraging trips undertaken outside of the egg development period. Our results highlight the need for more research into the factors attracting egg-producing females to the PLE foraging areas and the importance of trans-boundary marine protection for the conservation of vulnerable seabirds.