Urban Raptors Research Articles

Urban Parks Are Related to Functional and Phylogenetic Filtering of Raptor Assemblages in the Austral Pampas, Argentina

Urban parks are hot spots of bird diversity in cities. However, their role as urban filters for raptor species has not been assessed yet. This study aimed to compare the functional and phylogenetic traits of raptor assemblages in urban parks with the regional species pool of raptors in east–central Argentina. Diurnal raptors were surveyed in 51 urban parks in six cities during breeding and nonbreeding seasons. The regional species pool was assessed through raptor surveys and published maps surrounding the cities. The observed functional and phylogenetic relatedness of urban raptors was compared with 999 simulated raptor assemblages from the regional species pool. A total of five species were recorded in urban parks. The Chimango Caracara (Milvago chimango) was the numerically dominant species, comprising 95% of the 172 individuals recorded. The regional species pool was composed of 20 diurnal species. The functional and phylogenetic relatedness of urban raptors was higher than expected by chance, suggesting filtering induced by urban parks. Urban raptors were, in general, generalist species with small body sizes. Moreover, species tended to be part of the Falconidae family. Based on the results obtained here and in other published work, a model of raptor assembling in urban parks is proposed. The design of urban parks needs to be more heterogeneous, promoting the occurrence of specialist raptors.

The digital peregrine: A technonatural history of a cosmopolitan raptor

AbstractHumans, non‐human animals, and technologies are increasingly entangled. Using the peregrine falcon (Falco peregrinus) as an illustrative example, we propose ‘technonatural history’ as a theoretical and methodological approach for observing, describing, and examining the role technologies play in shaping human relations with other species. After nearing extinction in the 20th century, peregrines have become woven into the fabric of everyday urban life and are a frequently sighted urban raptor in the UK, nesting on high‐rise buildings and church spires since the late 1990s. Their unexpected presence in cities symbolises hope for multispecies conviviality amid the contemporary ecological crisis. As their populations resurged, crucially, webcam and livestreaming technologies developed rapidly. Peregrines were one of the first animals to be broadcast over the internet via ‘nestcams’, granting broad publics access to their intimate lives. We examine the related technological histories of livestreaming technologies and natural histories of peregrine falcons in the UK, tracing the emergence of ‘the digital peregrine’ and its manifold implications for more‐than‐human and digital geographies. To do so, we build on oral history interviews with people associated with digital peregrines throughout the UK: nestcam technicians, peregrine conservationists, professional ecologists, activists, and citizen scientists. While digitisation brings broad publics closer to these cosmopolitan raptors, they can only ever grasp at the wildness of peregrine falcons and their wider milieus as the digital peregrine is a distinct entity, encountered via its own set of affects and affordances. In the peregrine's case, digital technologies create unexpected and radical opportunities for urban conviviality, signalling the positive potentials technologies host for forging meaningful more‐than‐human connections.

What makes an urban raptor?

Raptor communities are negatively impacted by urbanization. However, some species can thrive in urban areas. Raptor species traits that favour their presence in urban areas have been scarcely studied. Moreover, phylogenetic relatedness may be a factor promoting raptor occurrence in urban areas. In this study, we use data gathered through citizen science in Argentina to analyse the phylogenetic signal and the drivers that correlate with raptor presence in urban settings. The mean percentage urban cover for the records of each species was considered as an index of raptor occurrence in urban areas. A total of 55 species were analysed, which accounted for 90% of the diurnal raptors of Argentina. Harris’s Hawk Parabuteo unicinctus, Pearl Kite Gampsonyx swainsonii and Chimango Caracara Milvago chimango had the highest urban index. Raptor occurrence in urban areas had a marginal phylogenetic signal, indicating a tendency for more closely related species to have similar tolerances to urbanization. The index of raptor occurrence in urban areas was highest for the most common species of non‐urban areas, and was not related to traits such as body mass, diet, nesting site and migratory behaviour. Our results highlight the importance of citizen science projects in data gathering at large geographical scales.

Community science data suggest the most common raptors (Accipitridae) in urban centres are smaller, habitat‐generalist species

As the world becomes more urbanized, identifying traits that allow some species to thrive in cities will be key to predicting which species will probably remain common and which may require conservation attention. Large, diverse, widely distributed and readily documented raptors represent an ideal taxonomic group to understand how species persist and thrive in urban areas. Global community science datasets can reveal patterns that might be obscured in studies limited to a small number of locations, those relying on presence/absence data or those conducted by a small number of observers. We analysed 127 species of raptors (hawks and related species; Family: Accipitridae) using recent community‐science (eBird) records from 59 cities on five continents, modelling two indices of occurrence with five ecological and life history traits, and incorporating phylogenetic relatedness. Based on previous studies of avian traits in urban vs. rural populations, and well as our casual observations of birds in cities across the USA and around the world, we hypothesized that urban raptor communities would be dominated by smaller, ecological‐generalist species regardless of the regional species pool. We defined urban occurrence in two ways: urban abundance (the frequency of breeding season reports within 10 km of a city centre) and species proportion (the relative abundance of each species in the local raptor community). We did not detect a strong phylogenetic signal for either urban occurrence index, suggesting that various unrelated raptor species may become common in cities of the world. In the best‐performing models, both urban indices were significantly negatively associated with body mass, and significantly positively associated with habitat breadth; species proportion was also significantly associated with nest substrate breadth. Our analysis suggests that there may be an ‘archetypal urban raptor’ and that species lacking these traits (e.g. large, specialist taxa) may be at greater conservation risk as global urbanization increases.

Behavioural factors underlying innovative problem-solving differences in an avian predator from two contrasting habitats.

Innovative behavior is considered one of the main factors facilitating the adaptation of animals to urban life. However, the relationship between urbanization and innovativeness is equivocal, perhaps reflecting aspects of urban environments that influence differently the behavioural traits underlying the occurrence of an innovation. In this work, we analysed the variation in innovative problem-solving performance between urban and rural individuals of the Caracara Chimango (Milvago chimango), with the goal of determining which behavioural trait (or combination) most explained such variation. We found that urban raptors outperformed rural ones in their solving speed and solving level (number of solutions) with a multiaccess box. They also showed more persistence, motor flexibility and diversity, as well as higher effectiveness in their solving attempts than rural chimangos. Sex was not an important factor. Urban chimangos showed less neophobia and spent more time exploring the box than rural birds during the initial habituation period, which probably determined the amount of information about the system that each individual had at the beginning of first problem solving trial. This difference in novelty response both directly and indirectly, through its relationship with persistence, motor flexibility and proportion of effective attempts, explained variability in solving performance. All individuals showed a decrease in solving latency, and an increase in solving level with experience, indicating that learning occurred in both raptor groups. This improvement occurred in parallel with changes in the afore-mentioned traits, though the pattern of improvement differed between urban and rural chimangos. We suggest that the characteristics of urban areas modulate the novelty response of chimangos, along with other correlated non-cognitive behavioural traits, which act in combination to increase the chances that novel problems could be quickly solved, and the resulting new behaviours established in city populations of this species.

Living in the concrete jungle: a review and socio-ecological perspective of urban raptor habitat quality in Europe

Raptors can be important components of urban ecosystems due to their role as apex predators, the presence of which may bring benefits to people. Urban environments may provide good quality habitats, and the raptors’ ability to utilize resources found here can contribute to their success. However, urban environments are socio-ecological systems and such mechanisms shaping habitats and ecological resources therein are less understood. This paper explores how raptors utilize urban resources, and the socio-ecological processes influencing their quality and availability. It begins with a systematic mapping of the literature to summarize the utility of urban resources by raptors with European distributions. Eighteen species were documented in the literature successfully exploiting novel hunting and/or nesting opportunities in both green and built-up locations of urban areas. We discuss how these may be consequential of human activities, some of which intentionally provided as subsidies, and how their utility by raptors create opportunities for human-raptor interactions further shaping public perception and decisions which potentially affect the raptors. Finally, we demonstrate these concepts by drawing on our experience from an urban peregrine falcon (Falco peregrinus) conservation site in London, UK. The paper concludes with a call for urban raptor conservation and research to consider social and ecological aspects together, appropriately reflecting urban environments as socio-ecological systems.

The Peregrine Returns: The Art and Architecture of an Urban Raptor Recovery

The Peregrine Returns: The Art and Architecture of an Urban Raptor Recovery

Linking landscape composition and biological factors with exposure levels of rodenticides and agrochemicals in avian apex predators from Germany

Intensification of agricultural practices has resulted in a substantial decline of Europe's farmland bird populations. Together with increasing urbanisation, chemical pollution arising from these land uses is a recognised threat to wildlife. Raptors are known to be particularly sensitive to pollutants that biomagnify and are thus frequently used sentinels for pollution in food webs. The current study focussed on anticoagulant rodenticides (ARs) but also considered selected medicinal products (MPs) and frequently used plant protection products (PPPs). We analysed livers of raptor species from agricultural and urban habitats in Germany, namely red kites (MIML; Milvus milvus), northern goshawks (ACGE; Accipiter gentilis) and Eurasian sparrowhawks (ACNI; Accipiter nisus) as well as white-tailed sea eagles (HAAL; Haliaeetus albicilla) and ospreys (PAHA; Pandion haliaetus) to account for potential aquatic exposures. Landscape composition was quantified using geographic information systems. The highest detection of ARs occurred in ACGE (81.3%; n = 48), closely followed by MIML (80.5%; n = 41), HAAL (38.3%; n = 60) and ACNI (13%; n = 23), whereas no ARs were found in PAHA (n = 13). Generalized linear models demonstrated (1) an increased probability for adults to be exposed to ARs with increasing urbanisation, and (2) that species-specific traits were responsible for the extent of exposure. For MPs, we found ibuprofen in 14.9% and fluoroquinolones in 2.3% in individuals that were found dead. Among 30 investigated PPPs, dimethoate (and its metabolite omethoate) and thiacloprid were detected in two MIML each. We assumed that the levels of dimethoate were a consequence of deliberate poisoning. AR and insecticide poisoning were considered to represent a threat to red kites and may ultimately contribute to reported decreased survival rates. Overall, our study suggests that urban raptors are at greatest risk for AR exposure and that exposures may not be limited to terrestrial food webs.

Nest boxes buffer the effects of climate on breeding performance in an African urban raptor.

As the world’s human population increases, transformation of natural landscapes into urban habitats continues to increase. In Africa, rates of human population growth and urbanisation are among the highest in the world, but the impacts of these processes on the continent’s biodiversity remain largely unexplored. Furthermore, the effects of ongoing anthropogenic climate change are likely to be severe and to interact with urbanisation. Some organisms appear resilient to urbanisation, and even proliferate in human-modified environments. One such species is the peregrine falcon Falco peregrinus in Cape Town, South Africa. Using a long-term data set (1989–2014), we investigate the relationship between breeding attempts, timing of breeding and breeding performance under varying weather conditions. Exploring these issues along an urbanisation gradient, we focus on the role of artificially provided nest boxes, and their capacity to buffer against extreme weather events. Pairs in more urbanised areas, and particularly those in nest boxes, were more likely to breed and to commence breeding earlier. Additionally, pairs using nest boxes were more likely to breed in years with higher rainfall. Warm and dry weather conditions generally advanced the timing of breeding, although this relationship with weather was not seen for urban pairs using nest boxes. Furthermore, weather did not impact breeding performance directly (breeding success and fledged brood size), but timing of breeding did, with earlier breeders producing more fledglings. Our study shows that falcons breeding in specially provided nest boxes were less sensitive to local weather dynamics than pairs using more natural nest sites. This has important implications as it suggests that the managed provision of such nesting sites can help this key urban species to cope with extreme weather events, which are predicted to increase with climate change.

Variation in boldness and novelty response between rural and urban predatory birds: The Chimango Caracara, Milvago chimango as study case

The study of traits that enable species to thrive in urban habitats is critical to a better understanding the evolution of urban ecosystems. Here, we examined variation in boldness, neophobia, and exploratory behavior in a generalist raptor, the Chimango Caracara, Milvago chimango, occurring in areas with different urbanization level. We also focused on the relationship between object exploration and neophobia in rural and urban population of this species. The results showed that birds from more urbanized habitats showed more tolerance to humans than rural raptors, without any effect of age and sex in this trait. Rural birds were also more neophobic and were slower to explore than urban raptors, though they dedicated a similar amount of time to exploring novel objects, indicating a non-correspondence between the speed to approach and contact these objects and the amount of exploration performed. Finally, we found a correlation between exploration speed and neophobia in rural birds, whereas for urban raptors this correlation was not observed. Our results show that urbanization not only influences the expression of risk-taking behaviors and novelty responses in the chimango, but can also modify the relationship between exploration and neophobia.

Urban Raptors: Ecology and Conservation of Birds of Prey in Cities

Urban Raptors: Ecology and Conservation of Birds of Prey in Cities

The population density of an urban raptor is inextricably tied to human cultural practices.

Human socio-cultural factors are recognized as fundamental drivers of urban ecological processes, but their effect on wildlife is still poorly known. In particular, human cultural aspects may differ substantially between the extensively studied urban settings of temperate regions and the poorly studied cities of the tropics, which may offer profoundly different niches for urban wildlife. Here, we report how the population levels of a scavenging raptor which breeds in the megacity of Delhi, the black kite Milvus migrans, depend on spatial variation in human subsidies, mainly in the form of philanthropic offerings of meat given for religious purposes. This tight connection with human culture, which generated the largest raptor concentration in the world, was modulated further by breeding-site availability. The latter constrained the level of resource-tracking by the kites and their potential ecosystem service, and could be used as a density-management tool. Similar ties between animal population densities, key anthropogenic resources and human beliefs may occur in thousands of cities all over the globe and may fit poorly with our current understanding of urban ecosystem functioning. For many urban animals, key resources are inextricably linked with human culture, an aspect that has been largely overlooked.

Human-attacks by an urban raptor are tied to human subsidies and religious practices

Growing urbanization is increasing human-wildlife interactions, including attacks towards humans by vertebrate predators, an aspect that has received extremely scarce investigation. Here, we examined the ecological, landscape and human factors that may promote human-aggression by raptorial Black kites Milvus migrans in the 16-millions inhabitants megacity of Delhi (India). Physical attacks depended on human activities such as unhygienic waste management, ritual-feeding of kites (mainly operated by Muslims), human density, and presence of a balcony near the nest, suggesting an association between aggression and frequent-close exposure to humans and derived food-rewards. Surprisingly, while more than 100,000 people could be at risk of attack in any given moment, attitudes by local inhabitants were strikingly sympathetic towards the birds, even by injured persons, likely as a result of religious empathy. These results highlight the importance of socio-cultural factors for urban biota and how these may radically differentiate the under-studied cities of developing countries from those of western nations, thus broadening our picture of human-wildlife interactions in urban environments. The rapid sprawling of urban and suburban areas with their associated food-subsidies is likely to increase proximity and exposure of large predators to humans, and vice versa, leading to heightened worldwide conflicts.

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.

Family morph matters: factors determining survival and recruitment in a long-lived polymorphic raptor.

From an evolutionary perspective, recruitment into the breeding population represents one of the most important life-history stages and ultimately determines the effective population size. In order to contribute to the next generation, offspring must survive to sexual maturity, secure a territory and find a mate. In this study, we explore factors influencing both offspring survival and their subsequent recruitment into the local breeding population in a long-lived urban raptor, the black sparrowhawk (Accipiter melanoleucus). Adult black sparrowhawks show discrete colour polymorphism (dark and light morphs), and in South Africa, morphs are distributed clinally with the highest proportion of dark morphs (c.75%) present in our study population on the Cape Peninsula. Parental morph was associated with both survival and recruitment. For survival, parental morph combination was important - with young produced by pairs of contrasting morphs having higher survival rates than young fledged from like-pairs. The association between recruitment and morph was more complex; with an interaction between male morph and breeding time, whereby recruitment of offspring from dark morph fathers was more likely when fledging earlier in the season. The opposite relationship was found for light morph fathers, with their offspring more likely to be recruited if fledged later in the season. This interaction may be due to differential morph-specific hunting success of fathers (males contribute most food provisioning), linked to background matching and crypsis in different weather conditions. Dark morph males may hunt more successfully in rainier and cloudier conditions, which occur more frequently earlier in the breeding season, and light morph males may be more successful later on, when weather conditions become increasingly brighter and drier. Our results reveal a complex situation whereby the family morph combination influences survival, and the father morphs specifically recruitment, revealing morph-specific benefits dependent on the timing of breeding. These empirical data are among the first to support the idea that differential fitness consequence of morph combination may explain balanced polymorphism in a vertebrate population.

Human-Related Threats to Urban Raptors

Abstract Annual bird mortality in the United States from anthropogenic sources is estimated at one billion. Urban raptors are affected by many of these factors; however, little is known about the relative frequency and magnitude of sources within and among species. I reviewed 86 published sources on mortality and urban use for the raptors of the United States and Canada. Within the Falconiformes (28 urban species), vehicle collisions and electrocutions were reported for most species (73% and 48%, respectively), and vehicular and window strikes were the leading sources of mortality for 39% and 12% of species, respectively. For the Strigiformes (14 urban species), vehicular (63%) and window (47%) collisions affected most species, and the primary sources of mortality were from vehicles (32%) and electrocution (5%). Window-strike mortality was reported for 45% of urban raptors and represented the leading source of mortality for Sharp-shinned Hawks (Accipiter striatus), Cooper's Hawks (A. cooperii), Merlins (F...

Feeding Activity and Seasonal Changes in Prey Composition of urban Peregrine FalconsFalco peregrinus

Despite the increasing populations of Peregrine Falcons in European cities, detailed quantitative studies of their diet composition and feeding activity in urban environments are rare. The results from observations in Warsaw have added to the knowledge of the feeding ecology of urban raptors. In 2000 and 2001 the same pair of Peregrines bred successfully in nest boxes situated on two different buildings in the city centre, rearing three and four chicks in the respective years. During the breeding seasons from hatching to fledging, the nests were monitored with a video camera. Only diurnal observations were used in the detailed analysis of feeding activity — 428 h in 2000 (33 days) and 384 h (24 days) in 2001. Two peaks of parental activity were noted: in the morning and in the afternoon. Additional data collected in 2000 showed that the falcons also fed their young at night. In 1998–2001 486 prey remains were collected on the buildings occupied by the Peregrines. In Warsaw these falcons preyed most often on Feral Pigeons (32%), and also on various thrush species (23.5%), Skylarks (8%) and Corncrakes (5.6%). Seasonal variations in prey composition were identified. During the spring and autumn migrations, the proportion of pigeons in the falcons' diet was 10–19%, while in summer and winter it was over 40%. The trend was reversed with regard to migrant species, which were prevalent in the diet in spring and autumn, but less numerous in summer and winter.