A conceptual framework for the colonisation of urban areas: the blackbird Turdus merula as a case study

Natural Patterns in the Dawn and Dusk Choruses of a Neotropical Songbird in Relation to an Urban Sound Environment

Urbanization is one of the more important phenomena affecting biodiversity in the Anthropocene. Some organisms can cope with urban challenges, and changes in birds' acoustic communication have been widely studied. Although changes in the timing of the daily organization of acoustic communication have been previously reported, there is a significant gap regarding possible variations in song structure between dawn and dusk choruses. Considering that urbanization imposes different soundscapes for dawn and dusk choruses, we postulate two hypotheses: (i) there are variations in song parameters between dawn and dusk choruses, and (ii) such parameters within the city will vary in response to urban noise. We studied urban and extra-urban populations of Chiguanco Thrush in La Paz, Bolivia, measuring in dawn and dusk choruses: song length; song sound pressure level; minimum, maximum, range and dominant frequency; and the number of songs per individual. The results support our two hypotheses: there were more songs, and songs were louder and had larger band widths at dawn than at dusk in urban and extra-urban populations. Urban Chiguanco Thrushes sing less, the frequency of the entire song rises, and the amplitude increases as compared with extra-urban Chiguanco Thrushes. Understanding variations between dawn and dusk choruses could allow for a better interpretation of how some bird species cope with urban challenges.

Toxoplasma gondii infection in ticks infesting migratory birds: the blackbird (Turdus merula) and the song thrush (Turdus philomelos)

Toxoplasmosis, caused by the protozoan Toxoplasma gondii, is the zoonosis widespread all over the world. Birds constitute an important group of T. gondii intermediate hosts often attacked by definitive hosts, e.g. domestic cats. Due to confirmation of an additional way of T. gondii transmission via tick bite, the aim of our study was to state and evaluate the infection prevalence of ticks feeding on blackbirds (Turdus merula) and song thrushes (Turdus philomelos). The real-time PCR amplification of the B1 gene fragment was used for detection of T. gondii infection in 157 Ixodes ricinus ticks removed from captured birds. The results showed the thrushes as hosts intensively attacked by ticks (prevalence 88.5% and 70% for blackbirds and song thrushes, respectively), and T. gondii infected individuals were detected. Among all ticks infected, 7 (5.8%; n = 120) were collected from blackbirds, and 2 (5.4%; n = 37) from song thrushes. The thrushes small body sizes and their tendency to urban ecosystems colonization, suggest that they relatively often become a pray of domestic cats, and combined with our findings, are potentially involved in maintenance the T. gondii population, especially in anthropogenic habitats, where the presence of toxoplasmosis is likely to constitute a serious danger to public health.

Little Owl Aggression and Territory in Urban and Rural Landscapes

Urbanization is a major land use change across the globe with vast effects on wildlife. In this paper, we studied (1) the territorial displays of Little Owls in urban and rural landscapes, analyzing also (2) the size and habitat composition of the territories, and (3) the factors affecting territory size in both landscapes. To do that, we used t-tests, Principal Components Analysis, and General Linear mixed model procedures. The territory size was smaller in urban than in rural landscapes. Urban territories of Little Owls are characterized by a lower cover of grassland, tall crops, short crops, gardens, and orchards, as well as a higher cover of built-up areas than territories in rural landscapes. Territory size in rural landscapes was negatively correlated with seasonal progress and positively correlated with altitude. The rate of territorial displays was similar between urban and rural territories; however, birds differentially utilized various structures. In urban territories, birds mostly used buildings, whereas in rural territories, birds used electric pylons and trees. The compositional differences between territories in the two landscapes may have important consequences for other behavior types and possibly reproductive output in this species.

The genomic response to urbanization in the damselfly Ischnura elegans

The complex and rapid environmental changes brought about by urbanization pose significant challenges to organisms. The multifaceted effects of urbanization often make it difficult to define and pinpoint the very nature of adaptive urban phenotypes. In such situations, scanning genomes for regions differentiated between urban and non-urban populations may be an attractive approach. Here, we investigated the genomic signatures of adaptation to urbanization in the damselfly Ischnura elegans sampled from 31 rural and urban localities in three geographic regions: southern and northern Poland, and southern Sweden. Genome-wide variation was assessed using more than 370,000 single nucleotide polymorphisms (SNPs) genotyped by ddRADseq. Associations between SNPs and the level of urbanization were tested using two genetic environment association methods: Latent Factors Mixed Models and BayPass. While we found numerous candidate SNPs and a highly significant overlap between candidates identified by the two methods within the geographic regions, there was a distinctive lack of repeatability between the geographic regions both at the level of individual SNPs and of genomic regions. However, we found "synapse organization" at the top of the functional categories enriched among the genes located in the proximity of the candidate urbanization SNPs. Interestingly, the overall significance of "synapse organization" was built up by the accretion of different genes associated with candidate SNPs in different geographic regions. This finding is consistent with the highly polygenic nature of adaptation, where the response may be achieved through a subtle adjustment of allele frequencies in different genes that contribute to adaptive phenotypes. Taken together, our results point to a polygenic adaptive response in the nervous system, specifically implicating genes involved in synapse organization, which mirrors the findings from several genomic and behavioral studies of adaptation to urbanization in other taxa.

Phylogeographic Patterns of Haemoproteid Assemblages of Selected Avian Hosts: Ecological and Evolutionary Implications

Background: While the dynamics of disease emergence is driven by host–parasite interactions, the structure and dynamics of these interactions are still poorly understood. Here we study the phylogenetic and morphological clustering of haemosporidian parasite lineages in a local avian host community. Subsequently, we examine geographical patterns of parasite assemblages in selected avian hosts breeding in Europe. Methods: We conduct phylogenetic and haplotype network analyses of Haemoproteus (Parahaemoproteus) lineages based on a short and an extended cytochrome b barcode region. Ordination analyses are used to examine changes in parasite assemblages with respect to climate type and geography. Results: We reveal relatively low phylogenetic clustering of haemoproteid lineages in a local avian host community and identify a potentially new Haemoproteus morphospecies. Further, we find that climate is effectively capturing geographical changes in parasite assemblages in selected widespread avian hosts. Moreover, parasite assemblages are found to vary distinctly across the host’s breeding range, even within a single avian host. Conclusions: This study suggests that a few keystone hosts can be important for the local phylogenetic and morphological clustering of haemoproteid parasites. Host spatio-temporal dynamics, both for partially and long-distance migratory birds, appear to explain geographical variation in haemoproteid parasite assemblages. This study also gives support to the idea that climate variation in terms of rainfall seasonality can be linked to the propensity for host switching in haemosporidians.

Spatial Distribution and Habitat Overlap of Five Columbidae Species in the Czech Republic

Simple Summary

The spatial distribution of species and their utilisation of resources are essential for better understanding species ecology. Using data gathered by ornithologists in Czech Republic, we studied land use type utilisation of five pigeons and doves. Our study aimed to understand which species and type of land use are positively associated and whether the species are positively associated with land use heterogeneity. Additionally, we quantified the amount of land use type utilisation by each species and their spatial overlap in these land use types. We hypothesised that the species would mostly overlap in farmlands and urban areas. We found an almost complete overlap between the domestic pigeon (Columba livia domestica) and the Eurasian collared dove (Streptopelia decaocto), as well as between the common wood pigeon (Columba palumbus) and the European turtle dove (Streptopelia turtur). We confirmed our hypothesis that the species distribution not only overlapped in farmlands and urban areas, but also in forests. Our study provides insight into these common species distributions and habitat affinities.

Abstract

Habitat overlap occurs when two species co-exist in the same habitat and utilise the same resources. Using common bird monitoring data in Czech Republic from 2015 and 2016, we compared the affinities of five Columbidae species regarding land use types. Moreover, we analysed the effects of land use types and land use heterogeneity on five species distributions. The aim of the study was to quantify the habitat overlap of five Columbidae species regarding types of land use and land use heterogeneity. We predicted a high level of habitat overlap between most of the species and its occurrence in farmlands and urban areas. Our results confirmed the high habitat overlap of all five Columbidae species in farmlands. An almost complete overlap was recorded between Columba livia domestica and Streptopelia decaocto, as well as between Columba palumbus and Streptopelia turtur. Considering land use utilisation, C. livia and S. decaocto mainly utilised farmlands and urban areas. Furthermore, deciduous forests were utilised by Columba oenas and coniferous and mixed forests by C. palumbus. Finally, S. turtur mainly utilised grasslands and avoided urban areas. We conclude that Columbidae species overlap in spatial distributions, mostly in urban areas, forests, and farmlands. Our study provides a summary of these common species habitat affinities.

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.

Urbanization processes drive divergence at the major histocompatibility complex in a common waterbird

Urban sprawl is one of the most common landscape alterations occurring worldwide, and there is a growing list of species that are recognised to have adapted to urban life. To be successful, processes of urban colonization by wildlife require a broad spectrum of phenotypic (e.g., behavioural or physiological) adjustments, but evidence for genetic adaptations is much scarcer. One hypothesis proposes that different pathogen-driven selective pressures between urban and non-urban landscapes leads to adaptations in host immune genes. Here, we examined urbanization-related differentiation at the key pathogen-recognition genes of vertebrate adaptive immunity-the major histocompatibility complex (MHC)-in a common waterbird, the Eurasian coot (Fulica atra). Samples were collected from an old urban population (established before the 1950s), a new urban population (established in the 2000s), and two rural populations from central Poland. We found strong significant divergence (as measured with Jost's D) at the MHC class II between the old urban population and the remaining (new urban and rural) populations. Also, there was a moderate, but significant divergence at the MHC between the new urban population and two rural populations, while no divergence was found between the two rural populations. The total number of MHC alleles and the number of private (population-specific) MHC alleles was lower in old urban populations, as compared to the rural ones. These patterns of differentiation at the MHC were not consistent with patterns found for neutral genetic markers (microsatellites), which showed few differences between the populations. Our results indicate that MHC allele composition depended on the level of anthropogenic disturbance and the time which passed since urban colonization, possibly due to the processes of genotype sorting and local adaptation. As such, our study contributes to the understanding of genetic mechanisms associated with urbanization processes in wildlife.

Modification of the third phase in the framework for vertebrate species persistence in urban mosaic environments

Urbanisation is rapidly transforming natural landscapes with consequences for biodiversity. Little is documented on the response of African wildlife to urbanisation. We reviewed case studies of vertebrate species' responses to urbanisation in KwaZulu-Natal, South Africa to determine trends. Connected habitat mosaics of natural and anthropogenic green spaces are critical for urban wildlife persistence. We present a novel modification to the final of three phases of the framework described by Evans et al. (2010), which documents this sequence for vertebrate species persistence, based on the perspective of our research. Species in suburbia exhibit an initial phase where behavioural and ecological flexibility, life-history traits and phenotypic plasticity either contribute to their success, or they stay at low numbers. Where successful, the next phase is a rapid increase in populations and distribution; anthropogenic food resources and alternate breeding sites are effectively exploited. The modified third phase either continues to spread, plateau or decline.

Blood Toxic Elements and Effects on Plasma Vitamins and Carotenoids in Two Wild Bird Species: Turdus merula and Columba livia

Birds have historically suffered adverse effects by toxic elements, such as As, Pb, Hg, and Cd. However, reports on exposure to a wide range of elements, including rare earth elements and other minor elements of emerging concern, and the potential consequences for wildlife are still scarce. This study evaluates blood concentrations of 50 elements and their related effects on lutein and vitamin levels in the Eurasian blackbird (Turdus merula) and wild rock pigeon (Columba livia), inhabiting different scenarios of contaminant exposure. Blood concentrations of As, Cd, and Pb (and Mn in T. merula) were increased in both species captured in the mining area, compared to the control site. T. merula also showed increased As, Cd, and Pb concentrations in blood in the agricultural–urban area, as compared to the control area, together with the highest Hg levels, which could be related to agricultural practices and industrial activities. Decreases of 33 and 38% in the plasma retinol levels in T. merula inhabiting the mining and the agricultural–urban areas, respectively, as compared to the control site, were associated with increased Pb, As, and Cd exposure. This could be due to a metal-driven suppressive effect in retinol metabolism and/or its over-use for coping with metal-related oxidative stress.

Colonization of Warsaw by the red fox Vulpes vulpes in the years 1976-2019

The red fox is one of the most adaptable carnivores inhabiting cities. The aim of our study was to describe the process of Warsaw colonization by the red fox. We focused on: (1) the fox distribution in Warsaw on the basis of presence-absence data (2005-2012) over a grid of 1 × 1 km², (2) the process of settlement in 29 green areas (study periods 1976-1978, 2004-2012, and 2016-2019) in relation to habitat type, and (3) temporal and spatial patterns of the red fox incidents (1998-2015) reported by Warsaw citizens. We found out that: (1) the red fox penetrated the whole city (i.e. its presence was confirmed in all squares of the grid), (2) 21% of the green areas were colonized in 1976-1978 but 93% in 2016-2019. Forests and riparian habitats were occupied more frequently than parks and cemeteries in 1976-1978 with no difference in the further years; (3) the probability of the fox incidents increased over years, was higher in June-October, on working days, and around noon, and with the share of discontinuous urban fabric in the buffers around incident locations. Nevertheless, the incidents only partially reflect population abundance trends and activity patterns of the species, so should be treated cautiously.

Decline in Distribution and Abundance: Urban Hedgehogs under Pressure

Simple Summary

Hedgehogs have been found in higher densities in urban compared to rural areas. Recent dramatic declines in rural hedgehog numbers lead us to pose the question: how are hedgehogs faring in urban areas? In this study, we examined how hedgehog numbers have changed in the city of Zurich, Switzerland, in the last 25 years. We compared data collected through citizen science projects conducted in 1992 and 2016–2018, including: observations of hedgehogs, data from footprint tunnels, and capture-mark recapture studies. We found that hedgehog numbers have declined by 41%, from the former average of more than 30 individuals per km², in the last 25 years. In the same time span, hedgehogs have lost 18% of their former urban distribution. The reasons for this decline are still unknown. Intensification of urban buildup, reduction of green space quality, the use of pesticides, parasites, or diseases, as well as increasing numbers of badgers, which are hedgehog predators, in urban areas are discussed as potential causes. Worryingly, these results suggest that hedgehogs are now under increasing pressure not only in rural but also in urban areas, their former refuges.

Abstract

Increasing urbanization and densification are two of the largest global threats to biodiversity. However, certain species thrive in urban spaces. Hedgehogs Erinaceus europaeus have been found in higher densities in green areas of settlements as compared to rural spaces. With recent studies pointing to dramatically declining hedgehog numbers in rural areas, we pose the question: how do hedgehogs fare in urban spaces, and do these spaces act as refuges? In this study, recent (2016–2018) and past (1992) hedgehog abundance and distribution were compared across the city of Zurich, Switzerland using citizen science methods, including: footprint tunnels, capture-mark recapture, and incidental sightings. Our analyses revealed consistent negative trends: Overall hedgehog distribution decreased by 17.6% ± 4.7%, whereas abundance declined by 40.6% (mean abundance 32 vs. 19 hedgehogs/km², in past and recent time, respectively), with one study plot even showing a 91% decline in this period (78 vs. 7 hedgehogs/km², respectively). We discuss possible causes of this rapid decline: increased urban densification, reduction of insect biomass, and pesticide use, as well as the role of increasing populations of badgers (a hedgehog predator) and parasites or diseases. Our results suggest that hedgehogs are now under increasing pressure not only in rural but also in urban areas, their former refuges.

Shelter availability and human attitudes as drivers of rock hyrax (Procavia capensis) expansion along a rural-urban gradient

While anthropogenic land-use changes threaten wildlife globally, some species take advantage of such changes and disperse into urban areas. The wildlife in urban areas often promotes conflicts with humans, notably when the animals are associated with the spread of zoonotic diseases. In Israel, current urban invasion of rock hyraxes (Procavia capensis) draws public attention, since the species is a reservoir host of cutaneous leishmaniasis, a serious skin disease. The rock hyrax, however, has seldom been studied in densely populated areas, and the drivers for its urban expansion, as well as its abilities to live and spread in core urban areas, are relatively unknown. Here, we explore the rock hyrax expansion to urban areas process by examining the availability, characteristics and use of shelter along an urban gradient. Our findings suggest that a series of factors determines shelter availability and quality for the rock hyrax, which facilitates its dispersion across the urban gradient. We found that rock hyraxes from the Judean Desert expand to the peri-urban region of Jerusalem by colonizing new rocky shelters formed as by-products of urban development. With their populations reaching extreme densities in this area and saturating the available shelters, there is some spill over to the adjacent core urban areas where they colonize littered sites, which are made available due to the local socio-economic conditions and cultural norms of waste disposal and illegal placement of temporary structures. Our work emphasizes the significance of the urban gradient approach for studying the mechanisms promoting wildlife expansion to cities. Our findings suggest that changes in shelter availability and quality due to urban development, and cultural norms promote shifts of the hyrax population by pushing from the already established areas and pulling into new environment across the urban gradient.

Plant species richness and composition of a habitat island within Lake Kastoria and comparison with those of a true island within the protected Pamvotis lake (NW Greece)

Lake Kastoria is one of the potentially “ancient” Balkan lakes that has a great environmental importance and ecological value, attracts high touristic interest and is under various anthropogenic pressures. It belongs to a Natura 2000 Special Protection Area and a Site of Community Interest. The city of Kastoria is located at the western part of the lake and just next to it, towards the centre of the lake, is a peninsula, a habitat island. In the framework of research concerning the flora of lake islands of Greece, one of the main objectives of the present study is to fill a gap concerning plant species richness of the habitat island within the protected Lake Kastoria, which is surrounded by the lake except for its north-western part where the border of the city of Kastoria is located. Floristic analysis of the habitat island of Lake Kastoria is in large measure accounted, concerning chorology with emphasis on Balkan endemics (8.7%), life forms, by hemicryptophytes (36.1%), therophytes (33.2%), phanerophytes (16.4%) and geophytes (10.9%) and, for habitats, by taxa preferring agricultural and ruderal ones (53.3%). Another objective is to compare its floristic composition to the one of the island within the protected urban Lake Pamvotis - one of the very few lake islands in Greece - focusing on the influence of urbanisation. The α- and β- diversity are measured in order to reveal floristic differences. Beta diversity partitioning in turnover and nestedness showed that the β-diversity is mostly expressed as compositional turnover. The role of the society in combination with long-term programmes for the study of plant species richness, functional diversity and patterns of species assemblages over time are necessary for the effective management and protection of protected areas, including lake insular areas.

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.

Evolution of genomic variation in the burrowing owl in response to recent colonization of urban areas

When a species successfully colonizes an urban habitat it can be expected that its population rapidly adapts to the new environment but also experiences demographic perturbations. It is, therefore, essential to gain an understanding of the population structure and the demographic history of the urban and neighbouring rural populations before studying adaptation at the genome level. Here, we investigate populations of the burrowing owl (Athene cunicularia), a species that colonized South American cities just a few decades ago. We assembled a high-quality genome of the burrowing owl and re-sequenced 137 owls from three urban-rural population pairs at 17-fold median sequencing coverage per individual. Our data indicate that each city was independently colonized by a limited number of founders and that restricted gene flow occurred between neighbouring urban and rural populations, but not between urban populations of different cities. Using long-range linkage disequilibrium statistics in an approximate Bayesian computation approach, we estimated consistently lower population sizes in the recent past for the urban populations in comparison to the rural ones. The current urban populations all show reduced standing variation in rare single nucleotide polymorphisms (SNPs), but with different subsets of rare SNPs in different cities. This lowers the potential for local adaptation based on rare variants and makes it harder to detect consistent signals of selection in the genome.

Offspring defense by an urban raptor responds to human subsidies and ritual animal-feeding practices

There is a growing interest in the behavioural and life history mechanisms that allow animal species to cope with rapidly expanding urban habitats, which impose frequent proximity to humans. A particular case of behavioral bottleneck (i.e. conflicting interests) faced by animals in urban environments is how they will modulate the defence of their offspring against the potential danger represented by humans, an aspect that has received scarce research attention. We examined the nest defense against humans by a dense breeding population of a raptor, the Black Kite Milvus migrans, within the megacity of Delhi (India). Here, kites live on a diet dominated by human waste and meat offered through religiously motivated bird feeding practices. Nest defense levels increased with the number of offspring, and with the progression of the breeding season. Defense also intensified close to ritual-feeding areas and with increasing human waste in the streets, suggesting synergistic effects of food availability, parental investment, personality-boldness and habituation to humans, with consequent attenuation of fear. Thus, the behavioural response to a perceived threat reflected the spatial mosaic of activity of humans in the city streets, their cultural practices of ritual-feeding, and their waste-management. For synurbic species, at the higher-end spectrum of adaptation to an urban life, human cultural practices and attitudes may well be the most defining dimensions of their urban niche. Our results suggest that, after initial urban colonization, animals may continue to adapt to the typically complex, heterogeneous environments of cities through fine-grained behavioural adjustments to human practices and activities.

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.

Great tits and the city: Distribution of genomic diversity and gene-environment associations along an urbanization gradient

Urbanization is a growing concern challenging the evolutionary potential of wild populations by reducing genetic diversity and imposing new selection regimes affecting many key fitness traits. However, genomic footprints of urbanization have received little attention so far. Using RAD sequencing, we investigated the genomewide effects of urbanization on neutral and adaptive genomic diversity in 140 adult great tits Parus major collected in locations with contrasted urbanization levels (from a natural forest to highly urbanized areas of a city; Montpellier, France). Heterozygosity was slightly lower in the more urbanized sites compared to the more rural ones. Low but significant effect of urbanization on genetic differentiation was found, at the site level but not at the nest level, indicative of the geographic scale of urbanization impact and of the potential for local adaptation despite gene flow. Gene-environment association tests identified numerous SNPs with small association scores to urbanization, distributed across the genome, from which a subset of 97 SNPs explained up to 81% of the variance in urbanization, overall suggesting a polygenic response to selection in the urban environment. These findings open stimulating perspectives for broader applications of high-resolution genomic tools on other cities and larger sample sizes to investigate the consistency of the effects of urbanization on the spatial distribution of genetic diversity and the polygenic nature of gene-urbanization association.

How weather instead of urbanity measures affects song trait variability in three European passerine bird species

Previous studies detected an influence of urban characteristics on song traits in passerine birds, that is, song adjustments to ambient noise in urban areas. Several studies already described the effect of weather conditions on the behavior of birds, but not the effect on song traits. We investigate, if song trait variability changes along a continuous urbanity gradient in Frankfurt am Main, Germany. We examined, for the first time on a larger scale, the influence of weather on song parameters. We made song recordings of three common passerine species: the blue and great tit (Cyanistes caeruleus (Linnaeus, 1758) and Parus major Linnaeus, 1758) and the European blackbird (Turdus merula Linnaeus, 1758). We measured different song traits and performed statistical analyses and modeling on a variety of variables-among them urbanity and weather parameters. Remarkably, we found only few cases of a significant influence of urbanity parameters on song traits. The influence of weather parameters (air pressure, atmospheric humidity, air and soil temperatures) on song traits was highly significant. Birds in Frankfurt face high noise pollution and might show different adaptations to high noise levels. The song trait variability of the investigated species is affected more by weather conditions than by urban characteristics in Frankfurt. However, the three species react differently to specific weather parameters. Smaller species seem to be more affected by weather than larger species.

Long-term study of the prevalence of Borrelia burgdorferi s.l. infection in ticks (Ixodes ricinus) feeding on blackbirds (Turdus merula) in NE Poland

Seeking evidence to confirm that blackbirds (Turdus merula) may be involved in environmental maintenance of Borrelia burgdorferi s.l. (the causative agent of Lyme borreliosis), we conducted a long-term study over three separate 2-year periods, together embracing a span of almost 20 years, all in the same area in northeastern Poland. We examined a total of 78 blackbirds and collected 623 Ixodes ricinus ticks feeding on them. The tick infestation prevalence was found to be very high (89.7 %). Among all ticks collected, 9.8 % individuals were infected with B. burgdorferi s.l. spirochetes. We found statistically significant growth in the prevalence of infected ticks as well as an increasing proportion of blackbirds hosting them in subsequent years of study. Ticks feeding on blackbirds were infected mainly with B. garinii (45.7 %), a genospecies commonly encountered in birds, and with B. afzelii (28.6 %), until recently considered rodent-associated. We also identified B. turdi (22.9 %), frequently found in recent years in ticks feeding on birds, and B. spielmanii (2.8 %), which had previously not been found in infected ticks feeding on blackbirds. We also found that ticks infected with genospecies associated with avian reservoir groups (B. garinii and B. turdi) were not randomly distributed on blackbirds, but instead focused on certain bird specimens. We therefore conjecture that this is a result of ticks becoming infected either from the host blackbird itself, or from other infected ticks feeding on the same host blackbird. We did not find any similar dependency for the rodent specialist B. afzelii.

Habitat preferences of two sparrow species are modified by abundances of other birds in an urban environment

Every species has certain habitat requirements, which may be altered by interactions with other co-occurring species. These interactions are mostly ignored in predictive models trying to identify key habitat variables correlated with species population abundance/occurrence. We investigated how the structure of the urban landscape, food resources, potential competitors, predators, and interaction between these factors influence the abundance of house sparrow Passer domesticus and the tree sparrow P. montanus in sixty 25 ha plots distributed randomly across residential areas of the city of Poznań (Poland). The abundance of the house sparrow was positively correlated with the abundance of pigeons but negatively correlated with human-related food resources. There were significant interaction terms between abundances of other urban species and habitat variables in statistical models. For example, the abundance of house sparrow was negatively correlated with the abundance of corvids and tree sparrows but only when food resources were low. The abundance of tree sparrows positively correlated with density of streets and the distance from the city center. The abundance of this species positively correlated with the abundance of corvids when food resources were low but negatively correlated at low covers of green area. Our study indicates that associations between food resources, habitat covers, and the relative abundance of two sparrow species are altered by the abundance of other urban species. Competition, niche separation and social facilitation may be responsible for these interactive effects. Thus, biotic interactions should be included not only as an additive effect but also as an interaction term between abundance and habitat variables in statistical models predicting species abundance and occurrence.

Does light pollution alter daylength? A test using light loggers on free-ranging European blackbirds (Turdus merula)

Artificial light at night is one of the most apparent environmental changes accompanying anthropogenic habitat change. The global increase in light pollution poses new challenges to wild species, but we still have limited understanding of the temporal and spatial pattern of exposure to light at night. In particular, it has been suggested by several studies that animals exposed to light pollution, such as songbirds, perceive a longer daylength compared with conspecifics living in natural darker areas, but direct tests of such a hypothesis are still lacking. Here, we use a combination of light loggers deployed on individual European blackbirds, as well as automated radio-telemetry, to examine whether urban birds are exposed to a longer daylength than forest counterparts. We first used activity data from forest birds to determine the level of light intensity which defines the onset and offset of daily activity in rural areas. We then used this value as threshold to calculate the subjective perceived daylength of both forest and urban blackbirds. In March, when reproductive growth occurs, urban birds were exposed on average to a 49-min longer subjective perceived daylength than forest ones, which corresponds to a 19-day difference in photoperiod at this time of the year. In the field, urban blackbirds reached reproductive maturity 19 day earlier than rural birds, suggesting that light pollution could be responsible of most of the variation in reproductive timing found between urban and rural dwellers. We conclude that light at night is the most relevant change in ambient light affecting biological rhythms in avian urban-dwellers, most likely via a modification of the perceived photoperiod.

Commonness and ecology, but not bigger brains, predict urban living in birds

Background

Several life history and ecological variables have been reported to affect the likelihood of species becoming urbanized. Recently, studies have also focused on the role of brain size in explaining ability to adapt to urban environments. In contrast, however, little is known about the effect of colonization pressure from surrounding areas, which may confound conclusions about what makes a species urban. We recorded presence/absence data for birds in 93 urban sites in Oslo (Norway) and compared these with species lists generated from 137 forest and 51 farmland sites surrounding Oslo which may represent source populations for colonization.

Results

We found that the frequency (proportion of sites where present) of a species within the city was strongly and positively associated with its frequency in sites surrounding the city, as were both species breeding habitat and nest site location. In contrast, there were generally no significant effects of relative brain mass or migration on urban occupancy. Furthermore, analyses of previously published data showed that urban density of birds in six other European cities was also positively and significantly associated with density in areas outside cities, whereas relative brain mass showed no such relationship.

Conclusions

These results suggest that urban bird communities are primarily determined by how frequently species occurred in the surrounding landscapes and by features of ecology (i.e. breeding habitat and nest site location), whereas species’ relative brain mass had no significant effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12898-015-0044-x) contains supplementary material, which is available to authorized users.

Urbanized birds have superior establishment success in novel environments

Many animals have adapted to the proximity of humans and thereby gained an advantage in a world increasingly affected by human activity. Numerous organisms have invaded novel areas and thereby increased their range. Here, we hypothesize that an ability to thrive in urban habitats is a key innovation that facilitates successful establishment and invasion. We test this hypothesis by relating the probability of establishment by birds on oceanic islands to the difference in breeding population density between urban and nearby rural habitats as a measure of urbanization in the ancestral range. This measure was the single-most important predictor of establishment success and the only statistically significant one, with additional effects of sexual dichromatism, number of releases and release effort, showing that the ability to cope with human proximity is a central component of successful establishment. Because most invasions occur as a consequence of human-assisted establishment, the ability to cope with human proximity will often be of central importance for successful establishment.

Steller sex: infidelity and sexual selection in a social Corvid (Cyanocitta stelleri)

Genetic analysis of avian mating systems has revealed that more than 70% of monogamous species show incidence of offspring parentage that does not match the social partner. Extra-pair parentage (EPP) has been linked to a variety of factors, including size and symmetry of ornamental traits, coloration, resource availability, and local conspecific density. We examined how ornamental plumage traits of individual Steller's jays (Cyanocitta stelleri) and territory characteristics influence genetic fidelity of socially monogamous pairs. We used seven highly polymorphic microsatellite markers to assign paternity to 79 offspring, and identified 12 (15.2%) as extra-pair young (EPY). Steller's jays with extra-pair young had significantly lower values of feather brightness and hue, indicating more ultraviolet-blue shifted coloration, and nested in closer proximity to the forest edge than Steller's jays with no detected EPY. Body size, crest height, asymmetry of ornamental crest stripes, as well as vegetative composition of territories and their proximity to supplemental feeders appeared to have little relationship to EPP. These results indicate that extra-pair parentage plays a role in the evolution of secondary sexual characteristics in both sexes, and suggest local density and availability of resources may influence Steller's jay mating dynamics.

Comparative cognition for conservationists

Every animal occupies a unique cognitive world based on its sensory capacities, and attentional and learning biases. Behaviour results from the interaction of this cognitive world with the environment. As humans alter environments, cognitive processes ranging from perceptual processes to learned behaviour govern animals' reactions. By harnessing animals' perceptual biases and applying insights from cognitive theory, we can purposefully alter cues to reduce maladaptive responses and shape behaviour. Despite the fundamental connection between cognition and behaviour, the breadth of cognitive theory is underutilised in conservation practice. Bridging these disciplines could augment existing conservation efforts targeting animal behaviour. We outline relevant principles of perception and learning, and develop a step-by-step process for applying aspects of cognition towards specific conservation issues.

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

Many organisms have invaded urban habitats, although the underlying factors initially promoting urbanization remain poorly understood. Partial migration may facilitate urbanization because such populations benefit from surplus food in urban environments during winter, and hence enjoy reduced fitness costs of migratory deaths. We tested this hypothesis in the European blackbird Turdus merula, which has been urbanized since the 19th century, by compiling information on timing of urbanization, migratory status, and population density for 99 cities across the continent. Timing of urbanization was spatially auto-correlated at scales up to 600 km. Analyses of timing of urbanization revealed that urbanization occurred earlier in partially migratory and resident populations than in migratory populations of blackbirds. Independently, this effect was most pronounced in the range of the distribution that currently has the highest population density, suggesting that urbanization facilitated population growth. These findings are consistent with the hypothesis that timing of urbanization is facilitated by partial migration, resulting in subsequent residency and population growth.

Wildlife strike risk assessment in several Italian airports: lessons from BRI and a new methodology implementation

The presence of wildlife in airport areas poses substantial hazards to aviation. Wildlife aircraft collisions (hereafter wildlife strikes) cause losses in terms of human lives and direct monetary losses for the aviation industry. In recent years, wildlife strikes have increased in parallel with air traffic increase and species habituation to anthropic areas. In this paper, we used an ecological approach to wildlife strike risk assessment to eight Italian international airports. The main achievement is a site-specific analysis that avoids flattening wildlife strike events on a large scale while maintaining comparable airport risk assessments. This second version of the Birdstrike Risk Index (BRI2) is a sensitive tool that provides different time scale results allowing appropriate management planning. The methodology applied has been developed in accordance with the Italian Civil Aviation Authority, which recognizes it as a national standard implemented in the advisory circular ENAC APT-01B.