Loss of migration and urbanization in birds: a case study of the blackbird (Turdus merula)

Anaplasma phagocytophilum in urban and peri-urban passerine birds in Ile-de-France

Wild animals in general, birds in particular, play a key role in transporting ticks and propagating tick-borne pathogens. Several studies have confirmed the infection of birds with Anaplasma phagocytophilum, with overall prevalence varying widely from country to country and/or study to study. This zoonotic bacterium, transmitted mainly by ticks of the genus Ixodes, is responsible for granulocytic anaplasmosis in humans (HGA) and domestic animals (cats, dogs, horses). The disease is also called tick-borne fever (TBF) in ruminants. Extremely rare in the USA, TBF is very common in Europe, where it causes economic losses in livestock. Conversely, HGA is well established in the USA whereas only a few less severe cases have been observed in Europe. Current typing techniques support the existence of multiple variants with differences in virulence/pathogenicity and tropism for certain tick and host species. However, epidemiological cycles remain difficult to characterize in Europe. Several studies describe a cycle apparently involving only birds in Europe, but no such study has been conducted in mainland France. Our objectives were to search for A. phagocytophilum in passerine birds in the Ile-de-France region and to explore their diversity using groEL and ankA gene typing and multilocus sequence typing (MLST). Various tissues (spleen, liver, and skin) were collected from cadavers of 680 passerines between March and December 2021. The presence of A. phagocytophilum was detected by qPCR Taqman targeting the msp2 gene. Three blackbirds (Turdus merula) were found positive, representing detection rates of 0.4 % in all birds tested and 3.3 % in blackbirds. The higher frequency of detection in blackbirds could be at least partially explained by their lifestyle, as they feed on the ground. Analysis of the results of groEL and ankA typing and MLST from positive blackbirds support the hypothesis that the avian A. phagocytophilum strains in Ile-de-France are distinct from those found in mammals, and that they form their own cluster in Europe.

Bidirectional tick transport by migratory birds of the African-Western Palearctic flyway over Turkish Thrace: observation of the current situation and future projection

This study was carried out at a vital stopover site of migrating birds in the Turkish Thrace, European part of Turkey, on the Mediterranean/Black Sea Flyway. Ticks were collected from the birds captured in the four migration periods, i.e., autumn 2020, spring 2021, autumn 2021, and spring 2022, and identified morphologically. Throughout the study, 10,651 birds from 77 species were examined, and 671 belonging to 34 species were found infested. The infestation prevalence in total birds and the mean number of ticks per infested bird were 6.3% and 3.8 (range: 1-142), respectively. A total of 2573 ticks were collected with the following species distribution and numbers: Ixodes spp. 70 larvae, I. frontalis 1829 larvae, 337 nymphs, and 30 adults, I. acuminatus 16 nymphs and 42 adults, I. ricinus 39 larvae, 141 nymphs, and one adult, Hyalomma spp. seven larvae and 60 nymphs, and Haemaphysalis sp. one larva. Prevalence, intensity, and species distribution of the ticks in birds varied depending on the month, season, year, and species-specific migration phenology of the birds. The results show that precise determination of the tick-borne risk associated with migratory birds for a particular region necessarily requires long-term and comprehensive studies and indicates that anthropogenic climate change and habitat degradation can significantly differentiate the risk by influencing the migration phenology in birds and by making new regions suitable for the establishment of different ticks.

Comparative immunocompetence and interspecies transmission of avian orthoavulavirus-1 in feral birds originating from rural and urban settings

Feral birds residing close to urban settings exhibit higher immunocompetence against environmental pathogens than their counterparts in rural areas. In this study, we comprehensively evaluated the immunocompetence of five specific feral bird species and investigated the potential for interspecies transmission and pathogenicity of Avian orthoavulavirus-1 (AOAV-1) originating from the Anseriformes order. The immunocompetence assessment involved administering the phytohemagglutinin (PHA) test to individual groups of birds from rural and urban settings, measuring patagium thickness at specific time intervals (12, 24, 36, 48, and 60 h) following the administration of 0.1 mL (1 mg/mL) of PHA. Urban birds displayed significantly enhanced mean swelling responses, particularly urban pigeons, which exhibited a significant difference in patagium thickness at all-time intervals except for 24 h (p = 0.000, p = 0.12). Similarly, rural and urban quails and crows showed substantial differences in patagium thickness at all-time intervals except for 12 h (p = 0.542, p = 0.29). For the assessment of interspecies transmission potential and pathogenicity, each feral bird group was separately housed with naive broiler birds (n = 10 each) and challenged with a velogenic strain of AOAV-1 isolate (Mallard-II/UVAS/Pak/2016) at a dose of 1 mL (108 EID50/mL). Urban birds demonstrated higher resistance to the virus compared to their rural counterparts. These findings highlight the specific immunocompetence of feral bird species and their potential contributions to AOAV-1 transmission and pathogenicity. Continuous monitoring, surveillance, and strict implementation of biosafety and biosecurity measures are crucial for effectively controlling AOAV-1 spillover to the environment and wild bird populations in resource-limited settings, particularly Pakistan.

Behavioral plasticity can facilitate evolution in urban environments

Plasticity-led evolution is central to evolutionary theory. Although challenging to study in nature, this process may be particularly apparent in novel environments such as cities. We document abundant evidence of plastic behavioral changes in urban animals, including learning, contextual, developmental, and transgenerational plasticities. Using behavioral drive as a conceptual framework, our analysis of notable case studies suggests that plastic behaviors, such as altered habitat use, migration, diurnal and seasonal activity, and courtship, can have faciliatory and cascading effects on urban evolution via spatial, temporal, and mate-choice mechanisms. Our findings highlight (i) the need to incorporate behavioral plasticity more formally into urban evolutionary research and (ii) the opportunity provided by urban environments to study behavioral mechanisms of plasticity-led processes.

No fry zones: How restaurant distribution and abundance influence avian communities in the Phoenix, AZ metropolitan area

Urbanization is one of the most widespread and extreme examples of habitat alteration. As humans dominate landscapes, they introduce novel elements into environments, including artificial light, noise pollution, and anthropogenic food sources. One understudied form of anthropogenic food is refuse from restaurants, which can alter wildlife populations and, in turn, entire wildlife communities by providing a novel and stable food source. Using data from the Maricopa Association of Governments and the Central Arizona-Phoenix Long Term Ecological Research (CAP LTER) project, we investigated whether and how the distribution of restaurants influences avian communities. The research aimed to identify restaurants, and thus the associated food they may provide, as the driver of potential patterns by controlling for other influences of urbanization, including land cover and the total number of businesses. Using generalized linear mixed models, we tested whether the number of restaurants within 1 km of bird monitoring locations predict avian community richness and abundance and individual species abundance and occurrence patterns. Results indicate that restaurants may decrease avian species diversity and increase overall abundance. Additionally, restaurants may be a significant predictor of the overall abundance of urban-exploiting species, including rock pigeon (Columba livia), mourning dove (Zenaida macroura), and Inca dove (Columbina Inca). Understanding how birds utilize anthropogenic food sources can inform possible conservation or wildlife management practices. As this study highlights only correlations, we suggest further experimental work to address the physiological ramifications of consuming anthropogenic foods provided by restaurants and studies to quantify how frequently anthropogenic food sources are used compared to naturally occurring sources.

Quantifying phenology and migratory behaviours of hummingbirds using single-site dynamics and mark-detection analyses

Nuanced understanding of seasonal movements of partially migratory birds is paramount to species and habitat conservation. Using nascent statistical methods, we identified migratory strategies of birds outfitted with radio-frequency identification (RFID) tags detected at RFID feeders in two sites in California, USA. We quantified proportions of migrants and residents and the seasonal phenology for each movement strategy in Allen's and Anna's hummingbirds; we also validated our methodology by fitting our model to obligate migratory black-chinned hummingbirds. Allen's and Anna's hummingbirds exhibited characteristics of facultative migratory behaviour. We also quantified apparent annual survival for each migratory strategy and found that residents had significantly higher probabilities of apparent survival. Low survival estimates for migrants suggest that a high proportion of birds in the migrant group permanently emigrated from our study sites. Considered together, our analyses suggest that hummingbirds in both northern and southern California sites partake in diverse and highly plastic migratory behaviours. Our assessment elucidates the dynamics underlying idiosyncratic migratory behaviours of two species of hummingbirds, in addition to describing a framework for similar assessments of migratory behaviours using the multi-state open robust design with state uncertainty model and single-site dynamics.

Long-Term Winter Population Trends of Corvids in Relation to Urbanization and Climate at Northern Latitudes

Simple Summary

Corvids (e.g., crows, magpies and jays) are an important part of urban settlements, especially during winter. To understand the factors affecting the long-term population trends of corvids, we counted wintering corvids in 31 human settlements along a 920 km latitudinal gradient in Finland during four winters between 1991 and 2020. We detected a total of five corvid species, from which the Hooded Crow, the Eurasian Magpie and the Eurasian Jackdaw were found to be common. During the study period, the number of Eurasian Jackdaws increased, and their distribution range moved northwards. No corresponding changes were observed for the Hooded Crow or the Eurasian Magpie. Neither the local-level urban-, climate- nor food-related factors correlated with the changes in the numbers and growth rates of the corvids. No interspecific interactions were observed. We assume that the Eurasian Jackdaw has benefitted from the decreased persecution, and probably also from the large-scale climate warming. Our results suggest that urban settlements are quite stable wintering environments for generalist and omnivorous corvids.

Abstract

Corvids (crows, magpies, jays) live in a close association with humans, and therefore knowledge about their population status and changes will be an essential part of monitoring the quality of urban environments. Wintering bird populations can track habitat and climate changes more rapidly than breeding populations. We conducted a long-term (1991–2020) winter census of corvid species in 31 human settlements along a 920 km latitudinal gradient in Finland. We observed a total of five corvid species: the Eurasian Magpie (occurring in 114 surveys out of 122; total abundance 990 ind.), the Hooded Crow (in 96 surveys; 666 ind.), the Eurasian Jackdaw (in 51 surveys; 808 ind.), the Eurasian Jay (in 5 surveys; 6 ind.) and the Rook (in 1 survey; 1 ind.). Only the numbers of the Eurasian Jackdaw differed between the study winters, being greater at the end of the study period (2019/2020) than during the earlier winters (1991/1992 and 1999/2000). The average growth rate (λ) of the Eurasian Jackdaw increased during the study period, whereas no changes were observed in the cases of the Hooded Crow or the Eurasian Magpie. The growth rate of the Eurasian Jackdaw was greater than that observed in the Finnish bird-monitoring work, probably because our data came only from the core area of each human settlement. Even though the number of buildings and their cover increased in the study plots, and the winter temperature differed between winters, the average growth rate (λ) of corvid species did not significantly correlate with these variables. These results suggest that urban settlements are stable wintering environments for the generalist corvids. The between-species interactions were all positive, but non-significant. Despite the total number of winter-feeding sites being greater during the winter of 1991/1992 than during the winter of 2019/2020, the changes in the numbers of feeding stations did not correlate with the growth rates of any corvid species. We assume that the Eurasian Jackdaw has benefitted from the decreased persecution, and probably also from large-scale climate warming that our study design was unable to take in to account. Our results indicated that wintering corvid populations succeed well in the human settlements in Finland. We recommend conducting long-term corvid research, also during breeding season, to understand more detailed causes of the population changes of corvids along an urban gradient. Without year-round long-term monitoring data, the conservation and management recommendations related to the corvid species in urban habitats may be misleading.

The Behavioral Responses of the Chiguanco Thrush to Urbanization in a Neotropical City Comes From Preadapted Behavioral Traits

Several animal species can survive within cities by changing their behavior; such changes could be the result of evolutionary adaptation, epigenetic effects, or come from preadapted traits through phenotypic plasticity or non-random dispersal. Exploring whether behavioral preadapted traits are present in non-urbanized populations could improve our understanding of the processes that allow animals to cope with urbanization. We compared the boldness, neophobia, and solving-test skills of adult individuals of the Chiguanco Thrush (Turdus chiguanco) between urban and extra-urban habitats in La Paz (Bolivia), a high-altitude Neotropical city. The urban Chiguanco Thrushes were bolder, less neophobic, and performed better in problem-solving tests. Extra-urban individuals varied significantly more among them in boldness and neophobia, and although a smaller proportion of individuals were able to solve the simplest problem-solving test, they did so in the same way as the urban ones. This evidence suggests that the behavioral responses of the Chiguanco Thrush to urbanization in La Paz come from preadapted traits.

Relationships Between Migration and Microbiome Composition and Diversity in Urban Canada Geese

Microbiome analysis presents an opportunity to understand how urban environments affect avian physiology. For example, habitat use can affect microbiome diversity and composition, and hosts with more diverse gut microbiota are thought to be more resistant to pathogens and have increased fitness. However, the microbiome is an understudied aspect of avian ecology, particularly in the context of migration and urbanization in wild birds. For this study, we hypothesized that, within urban birds, migrants would exhibit greater microbial diversity and inter-individual variation in microbiome composition than residents because they are exposed to more diverse habitats. We focused on Canada geese (Branta canadensis), one of many migratory species that exhibit increasingly more year-round residency in cities. We used 16S rRNA gene amplicon sequencing to quantify microbiome taxonomic composition in fecal samples from 32 GPS-tracked Canada geese, 22 of which were year-round residents of the Chicago area and 10 of which were migrants. Similar to recent studies on wild species feeding near human habitation, urban resident geese had higher gut microbial diversity than migrants. They also had increased inter-individual variation in microbiome composition and, on average, lower relative abundances of bacteria in the phylum Firmicutes, and the genera Terrisporobacter, Turicibacter, and Cellulosilyticum, which all have metabolic functions that may aid in goose digestion. Therefore, the gut microbiome of resident geese may provide fewer potential health benefits. These patterns may be a result of anthropogenic influences on aspects of resident goose ecology, such as diet, as well the influence of migration on migrant goose ecology and biology. Overall, our results suggest that reduced migration for urban-adapted wildlife species may have important consequences for physiology and health.

The evolutionary consequences of human-wildlife conflict in cities

Human-wildlife interactions, including human-wildlife conflict, are increasingly common as expanding urbanization worldwide creates more opportunities for people to encounter wildlife. Wildlife-vehicle collisions, zoonotic disease transmission, property damage, and physical attacks to people or their pets have negative consequences for both people and wildlife, underscoring the need for comprehensive strategies that mitigate and prevent conflict altogether. Management techniques often aim to deter, relocate, or remove individual organisms, all of which may present a significant selective force in both urban and nonurban systems. Management-induced selection may significantly affect the adaptive or nonadaptive evolutionary processes of urban populations, yet few studies explicate the links among conflict, wildlife management, and urban evolution. Moreover, the intensity of conflict management can vary considerably by taxon, public perception, policy, religious and cultural beliefs, and geographic region, which underscores the complexity of developing flexible tools to reduce conflict. Here, we present a cross-disciplinary perspective that integrates human-wildlife conflict, wildlife management, and urban evolution to address how social-ecological processes drive wildlife adaptation in cities. We emphasize that variance in implemented management actions shapes the strength and rate of phenotypic and evolutionary change. We also consider how specific management strategies either promote genetic or plastic changes, and how leveraging those biological inferences could help optimize management actions while minimizing conflict. Investigating human-wildlife conflict as an evolutionary phenomenon may provide insights into how conflict arises and how management plays a critical role in shaping urban wildlife phenotypes.

The Potential Role of Migratory Birds in the Rapid Spread of Ticks and Tick-Borne Pathogens in the Changing Climatic and Environmental Conditions in Europe

This opinion piece highlights the role of migratory birds in the spread of ticks and their role in the circulation and dissemination of pathogens in Europe. Birds with different lifestyles, i.e., non-migrants residing in a specific area, or short-, medium-, and long-distance migrants, migrating within one or several distant geographical regions are carriers of a number of ticks and tick-borne pathogens. During seasonal migrations, birds that cover long distances over a short time and stay temporarily in different habitats can introduce tick and pathogen species in areas where they have never occurred. An increase in the geographical range of ticks as well as the global climate changes affecting the pathogens, vectors, and their hosts increase the incidence and the spread of emerging tick-borne diseases worldwide. Tick infestations of birds varied between regions depends on the rhythms of tick seasonal activity and the bird migration rhythms determined by for example, climatic and environmental factors. In areas north of latitude ca. 58°N, immature Ixodes ricinus ticks are collected from birds most frequently, whereas ticks from the Hyalomma marginatum group dominate in areas below 42°N. We concluded that the prognosis of hazards posed by tick-borne pathogens should take into account changes in the migration of birds, hosts of many epidemiologically important tick species.

Assortative mating frames establishment in a young island bird population

Successful island colonizations are key events to understand range dynamic processes, but studying a young population right after it reaches establishment is a rare opportunity in natural systems. The genetic structure of a recently established population may offer unique insights into its colonization history and demographic processes that are important for a successful colonization. Here, we studied the population genetics of a recently established island population of Eurasian blackbirds (Aves: Turdus merula) located on the island of Heligoland in the German North Sea. Using microsatellites, we genotyped the majority of the island population, including the nestlings, over a 4-year period between 2004 and 2007. We also genotyped high numbers of migrants on stopover and mainland individuals, as they are potential founders of the island population. We identified two genetic clusters that comply with the migrating and mainland birds. While most of the island birds belong to the mainland cluster, some breeding individuals and a low fraction of the offspring belong to the genetic cluster found in migrating individuals with almost no admixture between the two, pointing to assortative mating acting on the island population. We did not find any evidence for founder events and detected deviations from the Hardy-Weinberg equilibrium that disappeared in cohorts of older age that coincide with a lower number of siblings in older cohorts. The observed genetic patterns unravel a complex colonization history to which migratory and mainland birds have contributed and which is characterized by assortative mating. Further research will be directed towards habitat selection and phenotypic differences as potential drivers of assortative mating in this island population.

Comparative urbanization of birds in China and Europe based on birds associated with trees

Urbanization effects on living organisms are spatially heterogeneous. Here we quantified the abundance of birds per tree in forested urban and rural habitats for 85,829 trees mainly in China and Europe. A population model was based on the assumption that: 1) birds have a normally distributed habitat preference; 2) an increase in population size linked to the habitat preference; 3) a population size dependent on the habitat preference; and 4) the removal of a certain fraction of individuals giving rise to extinction. We tested for large-scale differences in the impact of urbanization on the frequency distribution of the difference in abundance between urban and rural habitats in China and parts of Europe. The difference in the frequency distribution of urban population density of birds in trees minus rural population density of birds in trees in China and Europe was statistically significant, suggesting that the abundance of birds differed between trees in urban and rural habitats, but more so in China than in Europe. We hypothesize that more pronounced differences in China than in Europe may have arisen due to the Four Pests Campaign in 1958-1962 that resulted in death of hundreds of millions of birds (mainly tree sparrows Passer montanus, but also numerous other less common species that were starting to become urbanized around 1960). Species that were less common in 1960 could not sustain reductions in population size in urban areas and hence these species are still rare or absent in urban areas today 60 years later.

Urbanization, environmental stabilization and temporal persistence of bird species: a view from Latin America

Background

A scarcely studied consequence of urbanization is the effect of temporal stabilization of the environment on bird communities. This alteration is thought to dampen environmental variations between day and night, seasons and years, promoting a temporal persistence of bird composition in urban areas. The aim of this study was to review current evidence of temporal stabilization of biotic and abiotic factors in urban environments and the potential effects of such stabilization on temporal variation of bird species presence at different temporal scales.

Methods

I selected the literature by searching published articles and book chapters using Scopus and Google scholar. I only included articles that compared the temporal variation of bird composition or resources between different levels of urbanization.

Results

In general, there is evidence of temporal stabilization of abiotic and biotic factors at the three time scales considered. At the diurnal scale, the main factor considered was artificial light in the context of light pollution. At the seasonal and interannual scales, several case studies found a smaller temporal variation of primary productivity in urban than in natural and rural areas. Bird species composition showed more stabilization in urban environments at the three temporal scales: (1) several case studies reported bird activity at night, associated with artificial light; (2) studies in urban parks and along urbanization gradients showed smaller seasonal variation of bird composition in the more urbanized areas; and (3) in general, case studies along urbanization gradients showed smaller interannual variation of bird composition in the more urbanized areas, although some studies showed no relationships or opposite trends than expected.

Discussion

The published evidence suggests that urban areas dampen the natural cycles at several temporal scales. The stabilization of biotic and abiotic factors, such as light, temperature, food and habitat structure, is desynchronized from natural diurnal, seasonal and interannual cycles. However, there is a dearth of long-term comparisons of bird composition and studies that simultaneously analyze the relationship between resources and bird composition stabilization at the seasonal and interannual scales. More research is needed in the Southern hemisphere, where there is a lack of studies dealing with the seasonal and interannual variations of primary productivity along urbanization gradients and nocturnal activity of bird species. A future research agenda should include differentiation of spatial and temporal homogenization of avifaunas.

Evaluating the risk for Usutu virus circulation in Europe: comparison of environmental niche models and epidemiological models

Background

Usutu virus (USUV) is a mosquito-borne flavivirus, reported in many countries of Africa and Europe, with an increasing spatial distribution and host range. Recent outbreaks leading to regional declines of European common blackbird (Turdus merula) populations and a rising number of human cases emphasize the need for increased awareness and spatial risk assessment.

Methods

Modelling approaches in ecology and epidemiology differ substantially in their algorithms, potentially resulting in diverging model outputs. Therefore, we implemented a parallel approach incorporating two commonly applied modelling techniques: (1) Maxent, a correlation-based environmental niche model and (2) a mechanistic epidemiological susceptible-exposed-infected-removed (SEIR) model. Across Europe, surveillance data of USUV-positive birds from 2003 to 2016 was acquired to train the environmental niche model and to serve as test cases for the SEIR model. The SEIR model is mainly driven by daily mean temperature and calculates the basic reproduction number R₀. The environmental niche model was run with long-term bio-climatic variables derived from the same source in order to estimate climatic suitability.

Results

Large areas across Europe are currently suitable for USUV transmission. Both models show patterns of high risk for USUV in parts of France, in the Pannonian Basin as well as northern Italy. The environmental niche model depicts the current situation better, but with USUV still being in an invasive stage there is a chance for under-estimation of risk. Areas where transmission occurred are mostly predicted correctly by the SEIR model, but it mostly fails to resolve the temporal dynamics of USUV events. High R₀ values predicted by the SEIR model in areas without evidence for real-life transmission suggest that it may tend towards over-estimation of risk.

Conclusions

The results from our parallel-model approach highlight that relying on a single model for assessing vector-borne disease risk may lead to incomplete conclusions. Utilizing different modelling approaches is thus crucial for risk-assessment of under-studied emerging pathogens like USUV.

Electronic supplementary material

The online version of this article (10.1186/s12942-018-0155-7) contains supplementary material, which is available to authorized users.

Avian preference for close proximity to human habitation and its ecological consequences

Human proximity often have negative consequences for wildlife. However, animals may also benefit from human proximity in terms of availability of resources and protection against predators and parasites. We recorded the distance between all birds detected during the breeding season along 18 5-km transects and the nearest inhabited house in three areas of 50 km2 in Spain, France, and Denmark. More than three quarters of birds were located closer than 100 m to the nearest house, while the null expectation was less than a third. Mean distance for species was correlated with degree of bird urbanization and with flight initiation distance. Habitat specialist species with small breeding territories tended to live closer to houses. Birds from species having more broods per year, larger annual fecundity and lower nest predation rate lived closer to human habitation. Breeding range size, population density, and continental breeding population sizes were larger for species living closer to human habitation. Most relationships between distance to houses and bird traits had a strong phylogenetic signal, but most additive trait effects remained after phylogenetic correction. Proximity to human habitation was a main driver of the distribution of birds, with most individuals and species tightly linked to inhabited houses. Living close to human habitation was associated with success in the colonization of urban habitats and with consistent changes in distribution, abundance, behavior, and life history. Replicated measurements of the spatial and temporal variation in these distributions may be useful for monitoring and analyzing the ongoing process of organisms' urbanization.

Corticosterone levels in relation to trace element contamination along an urbanization gradient in the common blackbird (Turdus merula)

In a rapidly urbanizing world, trace element pollution may represent a threat to human health and wildlife, and it is therefore crucial to assess both exposition levels and associated effects of trace element contamination on urban vertebrates. In this study, we investigated the impact of urbanization on trace element contamination and stress physiology in a wild bird species, the common blackbird (Turdus merula), along an urbanization gradient (from rural to moderately urbanized areas). Specifically, we described the contamination levels of blackbirds by 4 non-essential (Ag, Cd, Hg, Pb) and 9 essential trace elements (As, Co, Cr, Cu, Fe, Mn, Ni, Se, Zn), and explored the putative disrupting effects of the non-essential element contamination on corticosterone levels (a hormonal proxy for environmental challenges). We found that non-essential trace element burden (Cd and Pb specifically) increased with increasing urbanization, indicating a significant trace element contamination even in medium sized cities and suburban areas. Interestingly, the increased feather non-essential trace element concentrations were also associated with elevated feather corticosterone levels, suggesting that urbanization probably constrains birds and that this effect may be mediated by trace element contamination. Future experimental studies are now required to disentangle the influence of multiple urban-related constraints on corticosterone levels and to specifically test the influence of each of these trace elements on corticosterone secretion.

Is supplementary feeding in gardens a driver of evolutionary change in a migratory bird species?

Human activities are causing rapid environmental change at a global scale. Urbanization is responsible for some of the most extreme human-altered habitats and is a known driver of evolutionary change, but evidence and understanding of these processes is limited. Here, we investigate the potential underlying mechanisms contributing to the contemporary evolution of migration behaviour in the Eurasian blackcap (Sylvia atricapilla). Blackcaps from central Europe have been wintering in urban areas of Britain with increasing frequency over the past 60 years, rather than migrating south to the Mediterranean. It has been hypothesized that the popularization of providing supplementary foods for wild birds within Britain may have influenced this marked migratory change, but quantifying the selective forces shaping evolutionary changes remains challenging. Using a long-term national scale data set, we examine both the spatial distribution and interannual variation in blackcap wintering behaviour in Britain in relation to supplementary food availability and local climate. Over a 12-year period, we show that blackcaps are becoming increasingly associated with the provision of supplementary foods in British gardens, and that the reliability of bird food supplies is influencing their winter distribution at a national scale. In addition, local climatic temperatures and broader scale weather variation are also important determinants of blackcap wintering patterns once they arrive in Britain. Based on our findings, we conclude that a synergistic effect of increased availability of feeding resources, in the form of garden bird food, coupled with climatic amelioration, has enabled a successful new wintering population to become established in Britain. As global biodiversity is threatened by human-induced environmental change, this study presents new and timely evidence of the role human activities can play in shaping evolutionary trajectories.

The fancy city life: Kuhl's pipistrelle, Pipistrellus kuhlii, benefits from urbanisation

Context Urbanisation is often regarded as a major threat to global biodiversity. Although wildlife is frequently affected by urbanisation, some species may actually benefit from it. Bats are among the commonest wild mammals in human-modified areas, and some species seem particularly well suited to exploit urban habitats where they find roosting and foraging opportunities. Aims We investigated habitat selection around roosts of synurbic Kuhl’s pipistrelles, Pipistrellus kuhlii, in Italy. Methods We measured the effects of the amount of urban habitat on bat reproductive timing and success in human-modified environments. Key results We found that P. kuhlii selects roosts surrounded by areas featuring urban habitats, especially those subject to urban development. Colonies in cities and suburbs advanced parturition time and produced more pups than those in rural areas. Permanent water sources and artificial lights in the surrounding habitats also seemed to favour the species reproductive success, particularly in developing urban areas. Conclusions Our results showed that this bat benefits from urbanisation and provided new insights on the effects of this major process on animal ecology and conservation in urban environments. Implications Although the ecological flexibility and positive response to urbanisation of P. kuhlii may help explain its recent range expansion, the role of climate change as a potential driver of this process has yet to be tested.