Successful city dwellers: a comparative study of the ecological characteristics of urban birds in the Western Palearctic

The power of community science to quantify ecological interactions in cities

Studying animals in urban environments is especially challenging because much of the area is private property not easily accessible to professional scientists. In addition, collecting data on animals that are cryptic, secretive, or rare is also challenging due to the time and resources needed to amass an adequate dataset. Here, we show that community science can be a powerful tool to overcome these challenges. We used observations submitted to the community science platform iNaturalist to assess predation and parasitism across urbanization gradients in a secretive, 'hard-to-study' species, the Southern Alligator Lizard (Elgaria multicarinata). From photographs, we quantified predation risk by assessing tail injuries and quantified parasitism by counting tick loads on lizards. We found that tail injuries increased with age and with urbanization, suggesting that urban areas are risky habitats. Conversely, parasitism decreased with urbanization likely due to a loss of hosts and anti-tick medications used on human companion animals. This community science approach generated a large dataset on a secretive species rapidly and at an immense spatial scale that facilitated quantitative measures of urbanization (e.g. percent impervious surface cover) as opposed to qualitative measures (e.g. urban vs. rural). We therefore demonstrate that community science can help resolve ecological questions that otherwise would be difficult to address.

Predation and Scavenging in the City: A Review of Spatio-Temporal Trends in Research

Many researchers highlight the role of urban ecology in a rapidly urbanizing world. Despite the ecological and conservation implications relating to carnivores in cities, our general understanding of their potential role in urban food webs lacks synthesis. In this paper, we reviewed the scientific literature on urban carnivores with the aim of identifying major biases in this topic of research. In particular, we explored the number of articles dealing with predation and scavenging, and assessed the geographical distribution, biomes and habitats represented in the scientific literature, together with the richness of species reported and their traits. Our results confirmed that scavenging is largely overlooked compared to predation in urban carnivore research. Moreover, research was biased towards cities located in temperate biomes, while tropical regions were less well-represented, a pattern that was more evident in the case of articles on scavenging. The species reported in both predation and scavenging articles were mainly wild and domestic mammals with high meat-based diets and nocturnal habits, and the majority of the studies were conducted in the interior zone of cities compared to peri-urban areas. Understanding the trophic role of carnivores in urban environments and its ecological consequences will require full recognition of both their predation and scavenging facets, which is especially desirable given the urban sprawl that has been predicted in the coming decades.

Which Traits Influence Bird Survival in the City? A Review

Urbanization poses a major threat to biodiversity worldwide. We focused on birds as a well-studied taxon of interest, in order to review literature on traits that influence responses to urbanization. We review 226 papers that were published between 1979 and 2020, and aggregate information on five major groups of traits that have been widely studied: ecological traits, life history, physiology, behavior and genetic traits. Some robust findings on trait changes in individual species as well as bird communities emerge. A lack of specific food and shelter resources has led to the urban bird community being dominated by generalist species, while specialist species show decline. Urbanized birds differ in the behavioral traits, showing an increase in song frequency and amplitude, and bolder behavior, as compared to rural populations of the same species. Differential food resources and predatory pressure results in changes in life history traits, including prolonged breeding duration, and increases in clutch and brood size to compensate for lower survival. Other species-specific changes include changes in hormonal state, body state, and genetic differences from rural populations. We identify gaps in research, with a paucity of studies in tropical cities and a need for greater examination of traits that influence persistence and success in native vs. introduced populations.

Consistent choice of landscape urbanization level across the annual cycle in a migratory waterbird species

Rapid urbanization has a great impact on avian distribution, ecology, habitat selection, and behavior. Recent avian studies indicated that individuals remain consistent in their behavioral responses to human disturbance across short periods of time. However, there is still little information about keeping consistent behaviors in distinct locations across different stages of the annual cycle. In this study, we aimed to test for long-term consistency in habitat selection with respect to urbanization in a migratory waterbird species, the Eurasian coot Fulica atra. For this purpose, we individually marked ca. 300 coots from four populations that varied in urbanization level and tracked their habitat preferences during the non-breeding season. We found that individuals from urban breeding populations selected habitats with a higher share of artificial areas during the non-breeding season, when compared to non-urban individuals. Also, a comparison of non-breeding sites selected by birds from our study populations with random sites showed that urban birds selected sites with higher urbanization level than resulting from random availability. Finally, we found a seasonal variation in habitat preferences in coots—individuals from all study populations selected more urbanized areas as the non-breeding season progressed. The results indicate that birds are able to remain consistent in habitat preferences not only at a large geographical scale, but also across different seasons. Marked between-population variation in habitat selection across the annual cycle may reflect personality differences of coots from urban and non-urban populations, and it stays in line with the personality-matching habitat choice hypothesis.

The impact of urbanization on body size of Barn Swallows Hirundo rustica gutturalis

Urbanization implies a dramatic impact on ecosystems, which may lead to drastic phenotypic differences between urban and nonurban individuals. For instance, urbanization is associated with increased metabolic costs, which may constrain body size, but urbanization also leads to habitat fragmentation, which may favor increases in body mass when for instance it correlates with dispersal capacity. However, this apparent contradiction has rarely been studied. This is particularly evident in China where the urbanization process is currently occurring at an unprecedented scale. Moreover, no study has addressed this issue across large geographical areas encompassing locations in different climates. In this regard, Barn Swallows (Hirundo rustica) are a suitable model to study the impact of urbanization on wild animals because they are a widely distributed species tightly associated with humans. Here, we collected body mass and wing length data for 359 breeding individuals of Barn Swallow (H. r. gutturalis) from 128 sites showing different levels of urbanization around the whole China. Using a set of linear mixed-effects models, we assessed how urbanization and geography influenced body size measured using body mass, wing length, and their regression residuals. Interestingly, we found that the impact of urbanization was sex-dependent, negatively affecting males' body mass, its regression residuals, and females' wing length. We also found that northern and western individuals were larger, regarding both body mass and wing length, than southern and eastern individuals. Females were heavier than males, yet males had slightly longer wings than females. Overall, our results showed that body mass of males was particularly sensitive trait to urbanization, latitude, and longitude, while it only showed a weak response to latitude in females. Conversely, while wing length showed a similar geographical pattern, it was only affected by urbanization in the case of females. Further research is needed to determine whether these phenotypic differences are associated with negative effects of urbanization or potential selective advantages.

Foraging in Urban Environments Increases Bactericidal Capacity in Plasma and Decreases Corticosterone Concentrations in White Ibises

As humans continue to infringe on natural habitats, more animals are exposed to urbanization and its associated challenges. It is still unclear, however, whether the movement of animals into urban habitats negatively influences the health and/or survival of those animals, however those animals often experience shifts in resource availability, diet composition, and exposure to stimuli that are new and potentially stressful. Recently, white ibises (Eudocimus albus) have become increasingly common in urban habitats where they forage in close proximity to humans and even interact with them, collecting food handouts. We hypothesized that foraging in urban habitats would negatively impact measures of health, impair innate immunity, trigger elevated concentrations of corticosterone, and depress physiological responses to stressors in white ibises. We found that plasma from birds captured from urban sites had higher bactericidal capacity against Escherichia coli than those captured in natural sites. Additionally, adults captured in urban habitats had a significantly lower baseline corticosterone concentrations during the post-breeding season, and corticosterone responses to a handling challenge were lower for birds captured from urban sites during year 2 of the study. These results indicate that exposure to urban habitats impacts ibis health, though in the opposite direction of what was predicted.

Big City Living: A Global Meta-Analysis Reveals Positive Impact of Urbanization on Body Size in Lizards

Urban environments pose different selective pressures than natural ones, leading to changes in animal behavior, physiology, and morphology. Understanding how animals respond to urbanization could inform the management of urban habitats. Non-avian reptiles have important roles in ecosystems worldwide, yet their responses to urbanization have not been as comprehensively studied as those of mammals and birds. However, unlike mammals and birds, most reptiles cannot easily move away from disturbances, making the selective pressure to adapt to urban environments especially strong. In recent years, there has been a surge in research on the responses of lizards to urbanization, yet no formal synthesis has determined what makes an urban lizard, in other words, which phenotypic traits are most likely to change with urbanization and in which direction? Here, we present a qualitative synthesis of the literature and a quantitative phylogenetic meta-analysis comparing phenotypic traits between urban and non-urban lizard populations. The most robust finding from our analysis is that urban lizards are larger than their non-urban counterparts. This result remained consistent between sexes and taxonomic groups. Hence, lizards that pass through the urban filter have access to better resources, more time for foraging, and/or there is selection on attaining a larger body size. Other results included an increase in the diameters of perches used and longer limb and digit lengths, although this may be a result of increased body size. Urban lizards were not bolder, more active or exploratory, and did not differ in immune responses than non-urban populations. Overall, studies are biased to a few geographic regions and taxa. More than 70% of all data came from three species of anoles in the family Dactyloidae, making it difficult to generalize patterns to other clades. Thus, more studies are needed across multiple taxa and habitats to produce meaningful predictions that could help inform conservation and management of urban ecological communities.

Urban ecophysiology: beyond costs, stress and biomarkers

Natural habitats are rapidly declining due to urbanisation, with a concomitant decline in biodiversity in highly urbanised areas. Yet thousands of different species have colonised urban environments. These organisms are exposed to novel urban conditions, which are sometimes beneficial, but most often challenging, such as increased ambient temperature, chemicals, noise and light pollution, dietary alterations and disturbance by humans. Given the fundamental role of physiological responses in coping with such conditions, certain physiological systems such as the redox system, metabolism and hormones are thought to specifically influence organisms' ability to persist and cope with urbanisation. However, these physiological systems often show mixed responses to urbanisation. Does this mean that some individuals, populations or species are resilient to the urban environmental challenges? Or is something missing from our analyses, leading us to erroneous conclusions regarding the impact of urbanisation? To understand the impact of urbanisation, I argue that a more integrated mechanistic and ecological approach is needed, along with experiments, in order to fully understand the physiological responses; without knowledge of their ecological and evolutionary context, physiological measures alone can be misinterpreted. Furthermore, we need to further investigate the causes of and capacity for individual plasticity in order to understand not only the impact of urbanisation, but also species resilience. I argue that abiotic and biotic urban factors can interact (e.g. pollution with micro- and macronutrients) to either constrain or relax individual physiological responses - and, thereby, plasticity - on a temporal and/or spatial scale, which can lead to erroneous conclusions regarding the impact of urbanisation.

Neurobiological and Ecological Correlates of Avian Innovation

In the wild, particularly in rapidly changing conditions, being capable of solving new problems can increase an animal's chances of survival and reproduction. In the current context of widespread habitat destruction and increasing urbanization, innovativeness might be a crucial trait. In the past few decades, birds have proven to be a model taxon for the study of innovation, thanks to the abundant literature on avian innovation reports. Innovation databases in birds have been successfully employed to assess associations between innovativeness and other traits such as invasion success, life history, generalism, and brain encephalization. In order to more directly assess the causes of variation in innovation, a complementary approach consists in measuring innovativeness in wild-caught animals using problem-solving tasks that mimic innovations in the field. This method can allow for finer scale evaluation of ecological and neural correlates of innovation. Here, I review some of the most important findings on the correlates of innovation, with a particular focus on neural ones. I conclude by discussing avenues for future research, which I suggest should focus on neurobiology.

Differences in body composition between urban and rural Mallards, Anas platyrhynchos

Anthropogenic feeding of wildlife provides a valuable opportunity for people to engage with animals, but such feeding has the potential to be detrimental to the species involved. Ducks are frequently fed at urban ponds globally, yet the health impacts of an urban lifestyle for birds are poorly documented. We studied urban and rural Mallards (Anas platyrhynchos) in the Manawatū-Whanganui region (New Zealand). Mallards are opportunistic omnivores that have a phenotypically flexible gastrointestinal system. As urban Mallards consume considerable amounts of low-fibre, high carbohydrate foods via anthropogenic feeding, we predicted that urban Mallards would have smaller gastrointestinal tract organs and higher fat levels than rural ducks. We compared gross body composition of Mallards in a modified environment with high levels of feeding by humans and in rural habitats. We also evaluated other health-associated aspects including fat deposit size, liver fat content and haemosiderin (liver iron deposit) levels. Contrary to predictions, urban birds had larger gizzards and caeca and were no fatter than rural birds; rural birds additionally had larger pectoralis major muscles. These differences are probably associated with broader ecological and behavioural factors than with the provision of anthropogenic food per se [in particular the presence of hard foods (acorns and nuts) for urban birds, and higher flight activity of rural birds]. Longer caeca in urban birds could, however, relate to immunity rather than microbial fermentation of cellulose. Overall, while the nature of the local environment does affect Mallard physiology, no detrimental effects of urban living were evident in this study.

Space use of wild boar (Sus Scrofa) in Budapest: are they resident or transient city dwellers?

In our study, we examined the movement of two wild boars marked with GPS/GSM transmitters in city of Budapest. We hypothesised that: the wild boars do not leave the urban area (H1); the wild boars prefer places that are less disturbed by people, and which are rich in potential hiding places (H2); and their home ranges would be smaller than that of wild boars living in non-urban environment (H3). Based on our results, we accepted our first hypothesis, as the wild boars had not left the area of Budapest. However, we partly rejected our second hypothesis: the wild boars preferred urban areas that were forested and richly covered with vegetation; however, human presence therefore disturbance was also high in those areas. The home range sizes of both marked wild boar sows were remarkably smaller than those of the wild boars living in natural environment (H3). City habitat modification, e.g. clearing undergrowth vegetation, could result that wild boars cannot find any hiding places. The significant part of food sources will disappear with the elimination of these places. By eliminating the two main factors together could prevent wild boars finding their living conditions within the city.

Fear and stressing in predator-prey ecology: considering the twin stressors of predators and people on mammals

Predators induce stress in prey and can have beneficial effects in ecosystems, but can also have negative effects on biodiversity if they are overabundant or have been introduced. The growth of human populations is, at the same time, causing degradation of natural habitats and increasing interaction rates of humans with wildlife, such that conservation management routinely considers the effects of human disturbance as tantamount to or surpassing those of predators. The need to simultaneously manage both of these threats is particularly acute in urban areas that are, increasingly, being recognized as global hotspots of wildlife activity. Pressures from altered predator-prey interactions and human activity may each initiate fear responses in prey species above those that are triggered by natural stressors in ecosystems. If fear responses are experienced by prey at elevated levels, on top of responses to multiple environmental stressors, chronic stress impacts may occur. Despite common knowledge of the negative effects of stress, however, it is rare that stress management is considered in conservation, except in intensive ex situ situations such as in captive breeding facilities or zoos. We propose that mitigation of stress impacts on wildlife is crucial for preserving biodiversity, especially as the value of habitats within urban areas increases. As such, we highlight the need for future studies to consider fear and stress in predator-prey ecology to preserve both biodiversity and ecosystem functioning, especially in areas where human disturbance occurs. We suggest, in particular, that non-invasive in situ investigations of endocrinology and ethology be partnered in conservation planning with surveys of habitat resources to incorporate and reduce the effects of fear and stress on wildlife.

Winter habitat selection of Corvids in an urban ecosystem

Urban areas attract birds during the winter when cities provide a predictable source of food and relatively stable weather conditions. However, many other factors determine the occurrence of birds in cities. This study analysed the relationship between corvids wintering in the city of Poznań, in western Poland and habitat features. Each of 32 research site was investigated three times. The most abundant species was the rook (mean = 17.4 individuals/site); the most frequent was the Eurasian magpie (88% of all sites). To determine variables that influence the abundance of birds, a set of generalised linear models was created, with model averaging being selected for each species. The abundance of hooded crows was positively influenced by surface of parks, water and by the length of tram tracks. The number of rooks was positively linked with the number of walnut trees, garbage cans and the surface of the water and negatively linked with the length of watercourses. Jackdaw was affected positively by the number of garbage cans, the surface of the water and negatively by the cover of trees. The number of magpies was associated with the number of walnut trees, garbage cans and negatively influenced by the surface of trees. None of the investigated habitat variables significantly affected the abundance of European jay. We also found a positive correlation between the abundances of hooded crow, rook, jackdaw and magpie. The results indicate that corvids wintering in urban ecosystems exhibit selectivity toward specific habitat features and that preferences differ among the studied species.

Beyond the landscape: Resistance modelling infers physical and behavioural gene flow barriers to a mobile carnivore across a metropolitan area

Urbanization affects key aspects of wildlife ecology. Dispersal in urban wildlife species may be impacted by geographical barriers but also by a species' inherent behavioural variability. There are no functional connectivity analyses using continuous individual-based sampling across an urban-rural continuum that would allow a thorough assessment of the relative importance of physical and behavioural dispersal barriers. We used 16 microsatellite loci to genotype 374 red foxes (Vulpes vulpes) from the city of Berlin and surrounding rural regions in Brandenburg in order to study genetic structure and dispersal behaviour of a mobile carnivore across the urban-rural landscape. We assessed functional connectivity by applying an individual-based landscape genetic optimization procedure. Three commonly used genetic distance measures yielded different model selection results, with only the results of an eigenvector-based multivariate analysis reasonably explaining genetic differentiation patterns. Genetic clustering methods and landscape resistance modelling supported the presence of an urban population with reduced dispersal across the city border. Artificial structures (railways, motorways) served as main dispersal corridors within the cityscape, yet urban foxes avoided densely built-up areas. We show that despite their ubiquitous presence in urban areas, their mobility and behavioural plasticity, foxes were affected in their dispersal by anthropogenic presence. Distinguishing between man-made structures and sites of human activity, rather than between natural and artificial structures, is thus essential for better understanding urban fox dispersal. This differentiation may also help to understand dispersal of other urban wildlife and to predict how behaviour can shape population genetic structure beyond physical barriers.

Reframing conservation physiology to be more inclusive, integrative, relevant and forward-looking: reflections and a horizon scan

Applying physiological tools, knowledge and concepts to understand conservation problems (i.e. conservation physiology) has become commonplace and confers an ability to understand mechanistic processes, develop predictive models and identify cause-and-effect relationships. Conservation physiology is making contributions to conservation solutions; the number of 'success stories' is growing, but there remain unexplored opportunities for which conservation physiology shows immense promise and has the potential to contribute to major advances in protecting and restoring biodiversity. Here, we consider how conservation physiology has evolved with a focus on reframing the discipline to be more inclusive and integrative. Using a 'horizon scan', we further explore ways in which conservation physiology can be more relevant to pressing conservation issues of today (e.g. addressing the Sustainable Development Goals; delivering science to support the UN Decade on Ecosystem Restoration), as well as more forward-looking to inform emerging issues and policies for tomorrow. Our horizon scan provides evidence that, as the discipline of conservation physiology continues to mature, it provides a wealth of opportunities to promote integration, inclusivity and forward-thinking goals that contribute to achieving conservation gains. To advance environmental management and ecosystem restoration, we need to ensure that the underlying science (such as that generated by conservation physiology) is relevant with accompanying messaging that is straightforward and accessible to end users.

Human influences on antipredator behaviour in Darwin's finches

Humans exert dramatic influences upon the environment, creating novel selective pressures to which organisms must adapt. On the Galapagos, humans have established a permanent presence and have altered selective pressures through influences such as invasive predators and urbanization, affecting iconic species such as Darwin's finches. Here, I ask two key questions: (a) Does antipredator behaviour (e.g., flight initiation distance - FID) change depending on whether invasive predators are historically absent, present, or eradicated? and (b) To what degree does urbanization affect antipredator behaviour? This study is one of the first to quantify antipredator behaviour in endemic species after the eradication of invasive predators. This will help to understand the consequences of invasive predator eradication and inform conservation measures. I quantified FID, an antipredator behaviour, in the small ground finch, across multiple islands in the Galapagos that varied in the presence, absence, or successful eradication of invasive predators. On islands with human populations, I quantified FID in urban and non-urban populations of finches. FID was higher on islands with invasive predators compared to islands with no predators. On islands from which invasive predators were eradicated ~11 years previously, FID was also higher than on islands with no invasive predators. Within islands that had both urban and non-urban populations of finches, FID was lower in urban finch populations, but only above a threshold human population size. FID in larger urban areas on islands with invasive predators was similar to or lower than FID on islands with no history of invasive predators. Overall, these results suggest that invasive predators can have a lasting effect on antipredator behaviour, even after eradication. Furthermore, the effect of urbanization can strongly oppose the effect of invasive predators, reducing antipredator behaviour to levels lower than found on pristine islands with no human influences. These results improve our understanding of human influences on antipredator behaviour which can help inform future conservation and management efforts on islands.

Nest site selection for five common birds and their coexistence in an urban habitat

Many species of birds gradually adapt to urbanization and colonize cities successfully. However, their nest site selection and competitive relationship in an urban community remain little known. Understanding the impact of urbanization on birds and the competitive relationship has important implications for the conservation and management of wildlife in urban ecosystems. Here, we undertook a systematic study to quantify nests in all species of birds in an urbanizing area of Nanchang, China. A total of 363 nests were detected in surveys including 340 nests of 16 bird species and 23 unidentified species nests. We mainly analyzed 5 dominant breeding birds with a sample size of >10 during the two breeding seasons (From April to July in 2016 and 2017), which included the light-vented bulbul, Chinese blackbird, scaly-breasted munia, spotted dove and grey-capped greenfinch. Most birds (93.66%) nested in the tree of artificial green belts, which seems to be the best breeding habitat for urban birds. Our results suggested that birds' breeding success relies on the trade-off between the benefit and the expense of specific stresses from habitats. The nest site selection of birds is also affected by the life habit of urban predators. Furthermore, competition among species can influence their distributions and utilization of environmental resources when birds nest in cities. We confirmed that the niche differentiation of five bird species in an urban environment makes them coexist successfully by utilizing various resources.

Urban living predicts behavioural response in a neotropical raptor

Behaviour is expected to be one of the most important factors driving urban living of bird species because it largely determines how animals interact with their environments. The contribution of different behavioural traits as facilitators of contemporary process of bird colonization of urban environments, however, is still unclear. Here we examined the differences in three behavioural traits: neophobia (avoidance of a new object) and solving success and solving latency of a problem solving test related to obtain food, in rural and urban living individuals of a common diurnal Neotropical raptor, the chimango caracara (Phalcoboenus chimango). Moreover, for solving success and solving latency behaviours, we tested the plasticity (i.e., habituation) in birds. Urban and rural chimangos showed similar neophobia of a new object. All chimangos showed an improvement in their output in problem-solving test as the five-day testing passed but urban chimangos showed higher solving capabilities than rural conspecifics as they were more successful in solving the problem test. More, urban birds shown lower solving latency than rural, as they were able to improve their test performance by opening doors in less time as the day passed; in rural birds this relation was not so abrupt. In addition, those individuals that opened more doors, opened these faster too. Lastly, both solving success and latency showed very low individual consistency (repeatability < 0.275). Our results provide evidence of plasticity in solving capabilities of chimango caracaras which reveal that a habituation process in these behavioural traits could be associated to establishment of birds in urban environments.

Habitat-related differences in song structure and complexity in a songbird with a large repertoire

Background

Urbanisation has been shown to influence many aspects of animal vocal communication. Much attention has been paid to anthropogenic noise, which is often described as one of the most challenging disturbances for urban dwellers. While a large body of literature describes associations between vocal behavior of avian populations and background noise level, most of these studies were conducted on species with relatively simple songs and small repertoire sizes. This study focuses on the song thrush, Turdus philomelos, a common Eurasian songbird with a complex singing style and large syllable repertoire. Our objective was to determine whether frequency, repertoire and temporal organisation of song parameters vary between birds inhabiting urban and adjacent forest habitats in which ambient noise levels differ.

Results

Songs of urban males were found to be more complex than in conspecifics from natural forest populations. Urban dwellers possessed greater syllable repertoires and repeated syllable sequences more often. In addition, they used a smaller proportion of whistles and a higher proportion of twitter syllables when singing compared to the nonurban males. Moreover, we found significant differences in the minimum and peak frequency of the whistle syllable between studied populations.

Conclusions

These findings may be an example of adaptation of acoustic communication in noisy urban environments, but we also discuss other possible explanations. We emphasize the need for further investigation into the relationships between birdsong and habitat characteristics, male quality, population density and ambient noise level in populations occupying urban and nonurban habitats.

The traits that predict the magnitude and spatial scale of forest bird responses to urbanization intensity

As humans continue moving to urban areas, there is a growing need to understand the effects of urban intensification on native wildlife populations. Forest species in remnant habitat are particularly vulnerable to urban intensification, but the mechanisms behind these effects are poorly understood. An understanding of how species traits, as proxies for mechanisms, mediate the effects of urban intensification on forest species can help fill this knowledge gap. Using a large point count dataset from the Second Pennsylvania Breeding Bird Atlas, we tested for the effects of species traits on the magnitude and spatial scale of the responses of 58 forest bird species to urbanization intensity in landscapes surrounding count locations. Average urbanization intensity effect size across species was -0.36 ± 0.49 (SE) and average scale of effect of urbanization intensity was 4.87 ± 5.95 km. Resident forest bird species that are granivorous or frugivorous, cavity-nesting, and have larger clutch sizes and more fledglings per clutch had more positive associations with increasing urbanization intensity in landscapes. In addition, the effect of urbanization intensity on forest birds manifested most strongly at larger spatial scales for granivorous, frugivorous, or omnivorous species that are cavity-nesting, have larger clutch sizes and longer wingspans, and flock in larger numbers. To our knowledge, the present study represents the first direct tests of the effects of species traits on both the magnitude and spatial scale of the effect of urbanization on forest birds, as well as the first evidence that migratory status, clutch size, wingspan, and fledglings per clutch are important determinants of the responses of forest birds to urbanization. We discuss the possible mechanisms underlying our results and their implications for forest bird conservation in urbanizing landscapes.

Effects of the Urban Environment on Oxidative Stress in Early Life: Insights from a Cross-fostering Experiment

As urban areas expand rapidly worldwide, wildlife is exposed to a wide range of novel environmental stressors, such as increased air pollution and artificial light at night. Birds in highly polluted and/or urbanized habitats have been found to have increased antioxidant protection, which is likely important to avoid accumulation of oxidative damage, which can have negative fitness consequences. Yet, the current knowledge about the ontogeny of antioxidant protection in urban areas is limited; i.e., is the capacity to up-regulate the antioxidant defences already established during pre-natal development, or does it manifest itself during post-natal development? We cross-fostered great tit (Parus major) nestlings within and between urban and rural habitats, to determine if oxidative stress (measured as non-enzymatic total antioxidant capacity, superoxide dismutase (SOD), and plasma lipid peroxidation) is affected by habitat of origin and/or by habitat of rearing. The results demonstrate that being reared in the urban environment triggers an increase in SOD (an intracellular, enzymatic antioxidant) independent of natal habitat. Oxidative damage increased with hatching date in urban-reared nestlings, but there was little seasonal change in rural-reared nestlings. Total antioxidant capacity was neither affected by habitat of rearing or habitat of origin, but we observed a decline with hatching date in both rearing habitats. Taken together, our results support the growing evidence that the urban environment induces a direct plastic adjustment in antioxidant protection, but that up-regulation is not sufficient to avoid increased oxidative damage in late-hatched broods. Future studies should explore the underlying causes for this effect in late-hatched broods and whether it has any negative long-term implications, both at the individual- and the population level.

A New Framework for Urban Ecology: An Integration of Proximate and Ultimate Responses to Anthropogenic Change

As urban areas continue to grow, understanding how species respond and adapt to urban habitats is becoming increasingly important. Knowledge of the mechanisms behind observed phenotypic changes of urban-dwelling animals will enable us to better evaluate the impact of urbanization on current and future generations of wildlife and predict how animals respond to novel environments. Recently, urban ecology has emerged not only as a means of understanding organismal adaptation but also as a framework for exploring mechanisms mediating evolutionary phenomena. Here, we have identified four important research topics that will advance the field of urban ecology and shed light on the proximate and ultimate causes of the phenotypic differences commonly seen among species and populations that vary in their responses to urbanization. First, we address the ecological and socio-economic factors that characterize cities, how they might interact with each other, and how they affect urban species. Second, we ask which are the proximate mechanisms underlying the emergence over time of novel traits in urban organisms, focusing on developmental effects. Third, we emphasize the importance of understanding the ultimate causations that link phenotypic shifts to function. This question highlights the need to quantify the strength and direction of selection that urban individuals are exposed to, and whether the phenotypic shifts associated with life in the city are adaptive. Lastly, we stress the need to translate how individual-level responses scale up to population dynamics. Understanding the mechanistic underpinnings of variation among populations and species in their responses to urbanization will unravel species resilience to environmental perturbation, which will facilitate predictive models for sustainability and development of green cities that maintain or even increase urban biodiversity and wildlife health and wellbeing.

Urbanisation as an important driver of nocturnal primate sociality

Urbanisation is an important factor driving species and biodiversity decline. Although habitat alterations can be detrimental for species, studies have shown that many diurnal primates are able to adapt to novel environments. Little is known about the ability of nocturnal primates to survive within an urban environment. To increase our understanding on this topic, we present ad libitum observations on group movement and sociality from urban and rural populations of the African lesser bushbaby (Galago moholi) in South Africa from 2014-2018. Our data show considerable changes in the social dynamics within urban bushbaby populations. In contrast to rural individuals, which spent the majority of their activity period solitarily or in pairs, urban individuals displayed a larger degree of sociality throughout their active period, forming groups of up to ten individuals. Furthermore, urban individuals spent less time moving around, while increasing social (communication/pair-grooming), foraging and feeding behaviour. Urban individuals fed on a range of different anthropogenic and natural food sources (insects/tree gum/nectar) compared to their rural counterparts. In summary, urban bushbabies showed a large degree of behavioural plasticity, with changes in social dynamics and structure frequently observed. Such alterations in sociality, along with the ability to utilise different feeding resources, may explain the ability of the species to survive within a highly altered environment.

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.

Shyer and larger bird species show more reduced fear of humans when living in urban environments

As the natural habitats of many species are degraded or disappear, there is scope for these species to be established in urban habitats. To ease the establishment and maintenance of urban populations of more species we need to better understand what degree of phenotypical change to expect as different species transition into urban environments. During the first stages of urban colonization, behavioural changes such as an increase in boldness are particularly important. A consistent response in urban populations is to decrease the distance at which individuals flee from an approaching human (flight initiation distance, or FID). Performing a phylogenetic generalized least-squares (PGLS) analysis on 130 avian species, I found that the largest changes in FID between rural and urban populations occur in species that are larger-bodied and naturally shy (higher rural FID), two phenotypic traits that are not normally associated with urban colonizers. More unlikely species may thus be able to colonize urban environments, especially if we design cities in ways that promote such urban colonizations.

Behavioral flexibility of a generalist carnivore

Innovative problem solving, repeated innovation, learning, and inhibitory control are cognitive abilities commonly regarded as important components of behaviorally flexible species. Animals exhibiting these cognitive abilities may be more likely to adapt to the unique demands of living in novel and rapidly changing environments, such as urbanized landscapes. Raccoons (Procyon lotor) are an abundant, generalist species frequently found in urban habitats, and are capable of innovative problem solving, which makes them an ideal species to assess their behavioral flexibility. We gave 20 captive raccoons a multi-access puzzle box to investigate which behavioral and cognitive mechanisms enable the generation of innovative and flexible behaviors in this species. Over two-thirds of raccoons tested were not only capable of innovative problem solving, but displayed repeated innovation by solving more than one solution on the multi-access puzzle box and demonstrated that they learned multiple solutions to a novel problem. Although we found no relationship between our measure of inhibitory control and a raccoon's ability to exhibit repeated innovations, we did find a positive relationship between the diversity of behaviors that an individual exhibited when interacting with the problem and the number of solution types that they solved. We identified other predictors of problem-solving performance, including neophobia and persistence. Finally, we examine the implications of our results in the context of the cognitive-buffer hypothesis and consider whether the widespread success of an adaptive generalist carnivore could be due in part to having these cognitive and behavioral traits.

One strategy does not fit all: determinants of urban adaptation in mammals

Urbanisation exposes wildlife to new challenging conditions and environmental pressures. Some mammalian species have adapted to these novel environments, but it remains unclear which characteristics allow them to persist. To address this question, we identified 190 mammals regularly recorded in urban settlements worldwide, and used phylogenetic path analysis to test hypotheses regarding which behavioural, ecological and life history traits favour adaptation to urban environments for different mammalian groups. Our results show that all urban mammals produce larger litters; whereas other traits such as body size, behavioural plasticity and diet diversity were important for some but not all taxonomic groups. This variation highlights the idiosyncrasies of the urban adaptation process and likely reflects the diversity of ecological niches and roles mammals can play. Our study contributes towards a better understanding of mammal association to humans, which will ultimately allow the design of wildlife-friendly urban environments and contribute to mitigate human-wildlife conflicts.

Estimating age-dependent survival when juveniles resemble females: Invasive ring-necked parakeets as an example

Many species only show sexual dimorphism at the age of maturity, such that juveniles typically resemble females. Under these circumstances, estimating accurate age-specific demographic parameters is challenging. Here, we propose a multievent model parameterization able to estimate age-dependent survival using capture-recapture data with uncertainty in age and sex assignment of individuals. We illustrate this modeling approach with capture-recapture data from the ring-necked parakeet Psittacula krameri. We analyzed capture, recapture, and resighting data (439 recaptures/resightings) of 156 ring-necked parakeets tagged with neck collars in Barcelona city from 2003 to 2016 to estimate the juvenile and adult survival rate. Our models successfully estimated the survival probabilities of the different age classes considered. Survival probability was similar between adults (0.83, 95% CI = 0.77-0.87) and juveniles during their second (0.79, 95% CI = 0.58-0.87) and third winter (0.83, 95% CI = 0.65-0.88). The youngest juveniles (1st winter) showed a slightly lower survival (0.57, 95% CI = 0.37-0.79). Among adults, females showed a slightly higher survival than males (0.87, 95% CI = 0.78-0.93; and 0.80, 95% CI = 0.73-0.86, respectively). These high survival figures predict high population persistence in this species and urge management policies. The analysis also stresses the usefulness of multievent models to estimate juvenile survival when age cannot be fully ascertained.

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.

Circulating corticosterone levels vary during exposure to anthropogenic stimuli and show weak correlation with behavior across an urban gradient in house finches (Haemorhous mexicanus)

Urban environments are rapidly expanding and presenting animal populations with novel challenges, many of which are thought to be stressors that contribute to low biodiversity. However, studies on stress responses in urban vs rural populations have produced mixed results, and many of these studies use a standard stressor that cannot be replicated in the wild (e.g. restraining an animal in a bag). Pairing physiological and behavioral measurements in response to urban-related stressors improves our understanding of the mechanism underlying animal success in human-dominated landscapes. Here, we examined the physiological stress (plasma corticosterone, CORT) responses of a songbird species (the house finch, Haemorhous mexicanus) to two different anthropogenic stimuli - (1) the presence of a human and (2) a captive environment containing man-made objects. During three field seasons (summer 2012, winter 2014, and winter 2015), we captured birds at six sites along an urban gradient in Phoenix, Arizona, USA and measured plasma CORT levels both before and after each trial. Though CORT levels did increase post-human exposure, though not during exposure to novel environment, indicating only one of the treatments caused a physiological response, baseline or post-trial plasma CORT levels did not differ between finches between urban and rural birds in 2012 or 2014. However, rural birds demonstrated relatively low pre- and post-trial plasma CORT levels during the human-exposure trials in 2015. Furthermore, we found few correlations between behavioral and physiological responses. A significant positive correlation was only detected between activity behavior after human approach and post-trial plasma CORT levels in 2012. Taken together, our results reveal a weak, conditional relationship between stress physiology, behavioral responses, and urbanization in house finches.