The breeding performance of raptors in urban landscapes: a review and meta-analysis

Abstract

Global urbanisation is rapidly increasing and can have profound impacts on wild flora and fauna. For many species, the impacts are detrimental and irreversible, whereas others are able to colonise and apparently thrive in these novel, human-made environments. Raptors are particularly susceptible to changes in the environment due to their position at the end of the food chain, yet some species are increasingly associated with towns and cities. To explore the impact of urbanisation on raptors, we reviewed the literature and compared breeding performance in urban and rural populations globally. In general, raptors began breeding earlier and had larger brood sizes in urban compared to rural environments. However, some of these raptors also fledged fewer young in urban habitats, apparently caused largely by a lack of prey and, in some cases, increased human disturbance. As such, urban environments may act as ecological traps for some raptor species. Species differed in their response to urbanisation. In particular, specialist bird predators such as Peregrine Falcons (Falco peregrinus) had a higher breeding performance (clutch size, brood size, number to fledge and nest success) and showed a positive response to urbanisation compared to those that predate on small mammals, such as Eurasian Kestrels (F. tinnunculus), which showed a negative response. This suggests that prey availability is one of the most important determinants of the success of urban-nesting raptors. We demonstrate a need for continued research into the breeding performance of raptors that live in urban environments, and stress the importance of focusing on the reasons for any differences in breeding performance between urban and non-urban environments in order to aid conservation and management efforts for this iconic bird group.

Impact of urbanization on abundance and phenology of caterpillars and consequences for breeding in an insectivorous bird

“…, Tomasevic and Marzluff , Kettel et al. ), with urban populations of insectivorous birds tending to have smaller clutches, and to produce fewer fledglings that have lower body mass compared to rural populations (Chamberlain et al. , Seress et al.…”

“…Several bird species lay earlier in urban areas, and it is hypothesized that in species that primarily feed their offspring with phytophagous insects earlier breeding is an adaptation to the earlier seasonal peaks in food availability in response to urban heat island effects (Vaugoyeau et al 2016). Although birds' reproductive success may be either increased, decreased, or not affected by urban development, this depends on the species' characteristics (Marzluff et al 2016, Tomasevic and Marzluff 2017, Kettel et al 2018, with urban populations of insectivorous birds tending to have smaller clutches, and to produce fewer fledglings that have lower body mass compared to rural populations (Chamberlain et al 2009, Seress et al 2012). These differences in reproductive success may be driven by changes in a range of environmental conditions, including temperature, food availability, nest predation, air pollution, and light pollution, but the precise nature of the mechanisms involved remain unclear (Gil and Brumm 2014).…”

Breeding performance of an apex predator, the peregrine falcon, across urban and rural landscapes

“…Peregrines in urban environments across Great Table 2 Britain were more successful than those in rural environments in terms of number of fledglings and nesting success. Indeed, the success of urban peregrine nests in this study (94 %) is the highest reported for any urban raptor species (Kettel et al 2018), or for rural peregrines in GB and elsewhere (e.g. Crick and Ratcliffe 1995;Amar et al 2012;Burke et al 2015).…”

“…Kettel et al (2018) highlight that while the breeding performance of small mammaleating raptors tends to be reduced in urban environments (e.g. Tella et al 1996;Liven-Schulman et al 2004;Charter et al 2007), the opposite is true for bird-eating raptors (e.g.…”

“…Even when species persist and manage to reproduce in urban environments, their breeding performance relative to traditional habitats can be highly variable across and within species (e.g. Chamberlain et al 2009;Kettel et al 2018). In some cases, urban populations do worse than those in traditional environments (e.g.…”