Disentangling the drivers of urban bird diversity in the non-breeding season: A general synthesis.

Current knowledge about the impacts of urbanisation on bird assemblages is based on evidence from studies partly or wholly undertaken in the breeding season. In comparison, the non-breeding season remains little studied, despite the fact that winter conditions at higher latitudes are changing more rapidly than other seasons. During the non-breeding season, cities may attract or retain bird species because they offer milder conditions or better feeding opportunities than surrounding habitats. However, the range of climatic, ecological and anthropogenic mechanisms shaping different facets of urban bird diversity in the non-breeding season are poorly understood. We explored these mechanisms using structural equation modelling to assess how urbanisation affects the taxonomic, phylogenetic and functional diversity of avian assemblages sampled worldwide in the non-breeding season. We found that minimum temperature, elevation, urban area and city age played a critical role in determining taxonomic diversity while a range of factors-including productivity, precipitation, elevation, distance to coasts and rivers, socio-economic (as a proxy of human facilitation) and road density-each contributed to patterns of phylogenetic and functional diversity. The structure and function of urban bird assemblages appear to be predominantly shaped by temperature, productivity and city age, with effects of these factors differing across seasons. Our results underline the importance of considering multiple hypotheses, including seasonal effects, when evaluating the impacts of urbanisation on biodiversity.

Urban birds' tolerance towards humans was largely unaffected by COVID-19 shutdown-induced variation in human presence.

The coronavirus disease 2019 (COVID-19) pandemic and respective shutdowns dramatically altered human activities, potentially changing human pressures on urban-dwelling animals. Here, we use such COVID-19-induced variation in human presence to evaluate, across multiple temporal scales, how urban birds from five countries changed their tolerance towards humans, measured as escape distance. We collected 6369 escape responses for 147 species and found that human numbers in parks at a given hour, day, week or year (before and during shutdowns) had a little effect on birds' escape distances. All effects centered around zero, except for the actual human numbers during escape trial (hourly scale) that correlated negatively, albeit weakly, with escape distance. The results were similar across countries and most species. Our results highlight the resilience of birds to changes in human numbers on multiple temporal scales, the complexities of linking animal fear responses to human behavior, and the challenge of quantifying both simultaneously in situ.

Dense city centers support less evolutionary unique bird communities than sparser urban areas.

Urbanization alters avian communities, generally lowering the number of species and contemporaneously increasing their functional relatedness, leading to biotic homogenization. Urbanization can also negatively affect the phylogenetic diversity of species assemblages, potentially decreasing their evolutionary distinctiveness. We compare species assemblages in a gradient of building density in seventeen European cities to test whether the evolutionary distinctiveness of communities is shaped by the degree of urbanization. We found a significant decline in the evolutionary uniqueness of avian communities in highly dense urban areas, compared to low and medium-dense areas. Overall, communities from dense city centers supported one million years of evolutionary history less than communities from low-dense urban areas. Such evolutionary homogenization was due to a filtering process of the most evolutionarily unique birds. Metrics related to evolutionary uniqueness have to play a role when assessing the effects of urbanization and can be used to identify local conservation priorities.

Spatial, temporal, and motivational changes due to the COVID-19 pandemic in a nature-based leisure activity - A global survey of birders.

Birdwatchers contribute an immense amount of data to citizen science databases. Thus, birding is important from the leisure perspective and from nature conservation. During the COVID-19 pandemic, we studied birdwatchers on a global scale in over 50 countries by applying the model of behavior change, which focuses on changes in opportunity (spatial, temporal), motivation, and capability (avoidance behavior). The sample consisted of 5051 participants (3437 men, 1575 women, mean age 49 years). Birders changed their spatial behavior to more local birding and to avoidance behavior by choosing different places and different clock times. Concerning motivation, being outdoors showed the highest increase and being with friends the strongest decrease. Higher specialized birders experienced a stronger shift toward regional birding. Birders that focused on new, local, or unrewarding places experienced an increase in motivation. Our study empirically supports the behavior change model and highlights the need to address the heterogeneity of the recreationists.

Spatial Overlap and Habitat Selection of Corvid Species in European Cities.

Understanding habitat and spatial overlap in sympatric species of urban areas would aid in predicting species and community modifications in response to global change. Habitat overlap has been widely investigated for specialist species but neglected for generalists living in urban settings. Many corvid species are generalists and are adapted to urban areas. This work aimed to determine the urban habitat requirements and spatial overlap of five corvid species in sixteen European cities during the breeding season. All five studied corvid species had high overlap in their habitat selection while still having particular tendencies. We found three species, the Carrion/Hooded Crow, Rook, and Eurasian Magpie, selected open habitats. The Western Jackdaw avoided areas with bare soil cover, and the Eurasian Jay chose more forested areas. The species with similar habitat selection also had congruent spatial distributions. Our results indicate that although the corvids had some tendencies regarding habitat selection, as generalists, they still tolerated a wide range of urban habitats, which resulted in high overlap in their habitat niches and spatial distributions.

EVI and NDVI as proxies for multifaceted avian diversity in urban areas.

Most ecological studies use remote sensing to analyze broad-scale biodiversity patterns, focusing mainly on taxonomic diversity in natural landscapes. One of the most important effects of high levels of urbanization is species loss (i.e., biotic homogenization). Therefore, cost-effective and more efficient methods to monitor biological communities' distribution are essential. This study explores whether the Enhanced Vegetation Index (EVI) and the Normalized Difference Vegetation Index (NDVI) can predict multifaceted avian diversity, urban tolerance, and specialization in urban landscapes. We sampled bird communities among 15 European cities and extracted Landsat 30-meter resolution EVI and NDVI values of the pixels within a 50-m buffer of bird sample points using Google Earth Engine (32-day Landsat 8 Collection Tier 1). Mixed models were used to find the best associations of EVI and NDVI, predicting multiple avian diversity facets: Taxonomic diversity, functional diversity, phylogenetic diversity, specialization levels, and urban tolerance. A total of 113 bird species across 15 cities from 10 different European countries were detected. EVI mean was the best predictor for foraging substrate specialization. NDVI mean was the best predictor for most avian diversity facets: taxonomic diversity, functional richness and evenness, phylogenetic diversity, phylogenetic species variability, community evolutionary distinctiveness, urban tolerance, diet foraging behavior, and habitat richness specialists. Finally, EVI and NDVI standard deviation were not the best predictors for any avian diversity facets studied. Our findings expand previous knowledge about EVI and NDVI as surrogates of avian diversity at a continental scale. Considering the European Commission's proposal for a Nature Restoration Law calling for expanding green urban space areas by 2050, we propose NDVI as a proxy of multiple facets of avian diversity to efficiently monitor bird community responses to land use changes in the cities.

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

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.

Flight initiation distance and refuge in urban birds.

Risk-taking in birds is often measured as the flight initiation distance (FID), the distance at which individuals take flight when approached by a potential predator (typically a human). The ecological factors that affect avian FID have received great attention over the past decades and meta-analyses and comparative analyses have shown that FID is correlated with body mass, flock size, starting distance of the approaching human, density of potential predators, as well as varying along rural to urban gradients. However, surprisingly, only few studies (mainly on reptiles and mammals) have explored effects of different types of refugia and their availability on animal escape decisions. We used Bayesian regression models (controlling for the phylogenetic relatedness of bird species) to explore changes in escape behaviour recorded in European cities in relationship to the birds' distance to the nearest refuge and distance fled to the refuge. In our analyses, we also included information on the type of refuge, built-up and vegetation cover, starting distance, flock size, urbanization level, and type of urban habitat. We found that birds preferred tree refuges over artificial and bush refuges. Birds escaped earlier if the distance to the nearest refuge of any type was longer and if birds fled longer distances to the refuge. FID was shorter when birds used bushes as refugia or landed on the ground after flushing compared to using artificial refugia. Similarly, the distance fled to a refuge was shortest when using bushes, and increased when escaping to artificial substrates and trees. Birds were more timid in suburban than core areas of cities, cemeteries than parks, and in areas with higher bush cover but lower cover of built-up areas and trees. Our findings provide novel information regarding the importance of refuge proximity and type as factors affecting the escape behaviour of urban birds.

Corvids in Urban Environments: A Systematic Global Literature Review.

Urbanization is one of the most prevalent drivers of biodiversity loss, yet few taxonomic groups are remarkably successful at adapting to urban environments. We systematically surveyed the global literature on the effects of urbanization on species of family Corvidae (crows, choughs, jackdaws, jays, magpies, nutcrackers, ravens, rooks, treepies) to assess the occurrence of corvids in urban environments and the factors affecting their success. We found a total of 424 primary research articles, and the number of articles has increased exponentially since the 1970s. Most studies were carried out in cities of Europe and North America (45.5% and 31.4%, respectively) and were directed on a single species (75.2). We found that 30 corvid species (23% of 133 total) regularly occur in urban environments. The majority (72%) of the studies reported positive effects of urbanization on corvids, with 85% of studies detecting population increases and 64% of studies detecting higher breeding success with urbanization. Of the factors proposed to explain corvids' success (availability of nesting sites and food sources, low predation and persecution), food availability coupled with diet shifts emerged as the most important factors promoting Corvidae to live in urban settings. The breeding of corvids in urban environments was further associated with earlier nesting, similar or larger clutches, lower hatching but higher fledging success, reduced home range size and limited territoriality, increased tolerance towards humans and increasing frequency of conflicts with humans. Despite geographic and taxonomic biases in our literature sample, our review indicates that corvids show both flexibility in resource use and behavioral plasticity that enable them to exploit novel resources for nesting and feeding. Corvids can thus be urban exploiters of the large-scale modifications of ecosystems caused by urbanization.

Patch, matrix and disturbance variables negatively influence bird community structure in small-sized managed green spaces located in urban core areas.

Patch, matrix and human-induced disturbance variables are important in determining the structure of urban bird communities. Although green spaces in urban core areas are usually small and disturbed, they can be important for local bird diversity. Because such areas are often overlooked, their study is critical for successfully incorporating biodiversity conservation in urban planning. Furthermore, comparing bird communities from different biogeographical areas would help identify generalizable patterns and propose common management actions. We compared the structure of breeding season bird assemblages of managed small public green spaces in the urban core areas of two similar-sized European cities, Kavala (Greece) and Rovaniemi (Finland), and studied the influence of environmental variables on community structure. Species composition differed between the cities. Abundance and evenness were higher in Kavala, while richness and diversity did not differ between the cities. Abundance did not respond in a general way to the same variables in the two cities. It increased with decreasing shrub cover and distance from the city center and with increasing midday noise and ground cover in Kavala, but increased with increasing distance from the city center and decreased with increasing car traffic and midday noise in Rovaniemi. This might be explained by the lower abundance of bird dwellers in Rovaniemi. Primarily gray cover, but also other variables, at both the patch and matrix levels (e.g., noise, car traffic, distance from the city center), negatively affected richness, evenness and diversity in both cities. Green space size was positively correlated with richness and diversity in Kavala, but not in Rovaniemi, possibly due to the smaller size variation in Rovaniemi. Results emphasized that increasing gray cover is harmful for birds in small-sized green spaces in urban core areas. However, urban managers should note that not all bird community metrics responded in similar ways to same environmental variables.

Effects of urbanization on taxonomic, functional and phylogenetic avian diversity in Europe.

Europe is an urbanized continent characterized by a long history of human-wildlife interactions. This study aimed to assess the effects of specific elements of urbanization and urban pollution on complementary avian diversity metrics, to provide new insights on the conservation of urban birds. Our study recorded 133 bird species at 1624 point counts uniformly distributed in seventeen different European cities. Our results thus covered a large spatial scale, confirming both effects of geographical and local attributes of the cities on avian diversity. However, we found contrasting effects for the different diversity components analyzed. Overall, taxonomic diversity (bird species richness), phylogenetic diversity and relatedness were significantly and negatively associated with latitude, while functional dispersion of communities showed no association whatsoever. At the local level (within the city), we found that urban greenery (grass, bush, and trees) is positively correlated with the number of breeding bird species, while the building cover showed a detrimental effect. Functional dispersion was the less affected diversity metric, while grass and trees and water (rivers or urban streams) positively affected the phylogenetic diversity of avian communities. Finally, the phylogenetic relatedness of species increased with all the main indicators of urbanization (building surface, floors, pedestrian's density and level of light pollution) and was only mitigated by the presence of bushes. We argue that maintaining adequate levels of avian diversity within the urban settlements can help to increase the potential resilience of urban ecosystems exposed to the stress provoked by rapid and continuous changes. We listed some characteristics of the cities providing positive and negative effects on each facet of urban avian diversity.

Face mask-wear did not affect large-scale patterns in escape and alertness of urban and rural birds during the COVID-19 pandemic.

Actions taken against the COVID-19 pandemic have dramatically affected many aspects of human activity, giving us a unique opportunity to study how wildlife responds to the human-induced rapid environmental changes. The wearing of face masks, widely adopted to prevent pathogen transmission, represents a novel element in many parts of the world where wearing a face mask was rare before the COVID-19 outbreak. During September 2020-March 2021, we conducted large-scale multi-species field experiments to evaluate whether face mask-use in public places elicits a behavioural response in birds by comparing their escape and alert responses when approached by a researcher with or without a face mask in four European countries (Czech Republic, Finland, Hungary, and Poland) and Israel. We also tested whether these patterns differed between urban and rural sites. We employed Bayesian generalized linear mixed models (with phylogeny and site as random factors) controlling for a suite of covariates and found no association between the face mask-wear and flight initiation distance, alert distance, and fly-away distance, respectively, neither in urban nor in rural birds. However, we found that all three distances were strongly and consistently associated with habitat type and starting distance, with birds showing earlier escape and alert behaviour and longer distances fled when approached in rural than in urban habitats and from longer initial distances. Our results indicate that wearing face masks did not trigger observable changes in antipredator behaviour across the Western Palearctic birds, and our data did not support the role of habituation in explaining this pattern.

SARS-CoV2 (COVID-19) Pandemic Lockdown Influences Nature-Based Recreational Activity: The Case of Birders.

The new corona virus infection SARS-CoV2 which was later renamed COVID-19 is a pandemic affecting public health. The fear and the constraints imposed to control the pandemic may correspondingly influence leisure activities, such as birding, which is the practice of observing birds based on visual and acoustic cues. Birders are people who carry out birding observations around the globe and contribute to the massive data collection in citizen science projects. Contrasting to earlier COVID-19 studies, which have concentrated on clinical, pathological, and virological topics, this study focused on the behavioral changes of birders. A total of 4484 questionnaire survey responses from 97 countries were received. The questionnaire had an open-ended style. About 85% of respondents reported that COVID-19 has changed their birding behavior. The most significant change in birdwatchers' behavior was related to the geographic coverage of birding activities, which became more local. People focused mostly on yard birding. In total, 12% of respondents (n = 542 cases) reported having more time for birding, whereas 8% (n = 356 cases) reported having less time for birding. Social interactions decreased since respondents, especially older people, changed their birding behavior toward birding alone or with their spouse. Women reported more often than men that they changed to birding alone or with their spouse, and women also reported more often about canceled fieldtrips or society meetings. Respondents from higher developed countries reported that they spend currently more time for birding, especially for birding alone or with their spouse, and birding at local hotspots. Our study suggests that long lockdowns with strict regulations may severely impact on leisure activities. In addition, a temporal and spatial shift in birding due to the pandemic may influence data quality in citizen science projects. As nature-based recreation will be directed more toward nearby sites, environmental management resources and actions need to be directed to sites that are located near the users, e.g., in urban and suburban areas. The results can be applied with caution to other nature-based recreational activities.

Biodiversity within the city: Effects of land sharing and land sparing urban development on avian diversity.

Urbanization, one of the most extreme human-induced environmental changes, is negatively affecting biodiversity worldwide, strongly suggesting that we should reconcile urban development with conservation. Urbanization can follow two extreme types of development within a continuum: land sharing (buildings mixed with dispersed green space) or land sparing (buildings interspersed with green patches that concentrate biodiversity-supporting vegetation). Recent local-scale studies indicate that biodiversity is typically favored by land sparing. We investigated which of these two types of urbanization is associated with a higher taxonomic (i.e. species richness), functional, and phylogenetic diversity of birds. To do so, we collected information on breeding and wintering bird assemblages in 45 land-sharing and 45 land-sparing areas in nine European cities, which provide the first attempt to explore this question using a large geographical scale and temporal replication. We found that land-sharing urban areas were significantly associated with a higher taxonomic and functional diversity of birds during winter, but not during the breeding season (with only a marginally significant effect for functional diversity). We found no association between the type of urban development and phylogenetic diversity. Our findings indicate that not all components of avian diversity are similarly affected by these two means of urban planning and highlight the importance of integrating the temporal perspective into this kind of studies. Our results also offer useful information to the current debate about the trade-off between biodiversity conservation and human well-being in the context of land sharing and sparing urban practices. In addition, we found that certain small-scale urban landscape characteristics (i.e. few impervious surfaces, high water or tree cover) and human practices (i.e. bird feeders or plants with berries) can help maintaining more diverse urban bird assemblages. We provide specific suggestions for both policymakers and citizens that hopefully will help to create more biodiversity-friendly cities in the future.

Land-sharing vs. land-sparing urban development modulate predator-prey interactions in Europe.

Urban areas are expanding globally as a consequence of human population increases, with overall negative effects on biodiversity. To prevent the further loss of biodiversity, it is urgent to understand the mechanisms behind this loss to develop evidence-based sustainable solutions to preserve biodiversity in urban landscapes. The two extreme urban development types along a continuum, land-sparing (large, continuous green areas and high-density housing) and land-sharing (small, fragmented green areas and low-density housing) have been the recent focus of debates regarding the pattern of urban development. However, in this context, there is no information on the mechanisms behind the observed biodiversity changes. One of the main mechanisms proposed to explain urban biodiversity loss is the alteration of predator-prey interactions. Using ground-nesting birds as a model system and data from nine European cities, we experimentally tested the effects of these two extreme urban development types on artificial ground nest survival and whether nest survival correlates with the local abundance of ground-nesting birds and their nest predators. Nest survival (n = 554) was lower in land-sharing than in land-sparing urban areas. Nest survival decreased with increasing numbers of local predators (cats and corvids) and with nest visibility. Correspondingly, relative abundance of ground-nesting birds was greater in land-sparing than in land-sharing urban areas, though overall bird species richness was unaffected by the pattern of urban development. We provide the first evidence that predator-prey interactions differ between the two extreme urban development types. Changing interactions may explain the higher proportion of ground-nesting birds in land-sparing areas, and suggest a limitation of the land-sharing model. Nest predator control and the provision of more green-covered urban habitats may also improve conservation of sensitive birds in cities. Our findings provide information on how to further expand our cities without severe loss of urban-sensitive species and give support for land-sparing over land-sharing urban development.

Contagious fear: Escape behavior increases with flock size in European gregarious birds.

Flight initiation distance (FID), the distance at which individuals take flight when approached by a potential (human) predator, is a tool for understanding predator-prey interactions. Among the factors affecting FID, tests of effects of group size (i.e., number of potential prey) on FID have yielded contrasting results. Group size or flock size could either affect FID negatively (i.e., the dilution effect caused by the presence of many individuals) or positively (i.e., increased vigilance due to more eyes scanning for predators). These effects may be associated with gregarious species, because such species should be better adapted to exploiting information from other individuals in the group than nongregarious species. Sociality may explain why earlier findings on group size versus FID have yielded different conclusions. Here, we analyzed how flock size affected bird FID in eight European countries. A phylogenetic generalized least square regression model was used to investigate changes in escape behavior of bird species in relation to number of individuals in the flock, starting distance, diet, latitude, and type of habitat. Flock size of different bird species influenced how species responded to perceived threats. We found that gregarious birds reacted to a potential predator earlier (longer FID) when aggregated in large flocks. These results support a higher vigilance arising from many eyes scanning in birds, suggesting that sociality may be a key factor in the evolution of antipredator behavior both in urban and rural areas. Finally, future studies comparing FID must pay explicit attention to the number of individuals in flocks of gregarious species.

Adjusting risk-taking to the annual cycle of long-distance migratory birds.

Life-history theory predicts that current behaviour affects future reproduction, implying that animals should optimise their escape strategies to reflect fitness costs and benefits of premature escape. Both costs and benefits of escape may change temporally with important consequences for the evolution of escape strategies. Moreover, escape strategies of species may differ according to their positions on slow-fast pace of life gradients. We studied risk-taking in long-distance migratory animals, waders (Charadriiformes), during the annual cycle, i.e., breeding in Europe, stopover in the Middle East and wintering in tropical Africa. Phylogenetically informed comparative analyses revealed that risk-taking (measured as flight initiation distance, FID) changed significantly over the year, being lowest during breeding and peaking at stopover sites. Similarly, relationships between risk-taking and life-history traits changed among stages of the annual cycle. While risk-taking significantly decreased with increasing body mass during breeding, risk-taking-body mass relationship became marginally significant in winter and disappeared during migration. The positive trend of risk-taking along slow-fast pace of life gradient measured as adult survival was only found during breeding. The season-dependent relationships between risk-taking and life history traits suggest that migrating animals respond to fluctuating environments by adopting behavioural plasticity.