Prey abundance and urbanization influence the establishment of avian predators in a metropolitan landscape

Abstract

Urbanization causes the simplification of natural habitats, resulting in animal communities dominated by exotic species with few top predators. In recent years, however, many predators such as hawks, and in the US coyotes and cougars, have become increasingly common in urban environments. Hawks in the Accipiter genus, especially, are recovering from widespread population declines and are increasingly common in urbanizing landscapes. Our goal was to identify factors that determine the occupancy, colonization and persistence of Accipiter hawks in a major metropolitan area. Through a novel combination of citizen science and advanced remote sensing, we quantified how urban features facilitate the dynamics and long-term establishment of Accipiter hawks. Based on data from Project FeederWatch, we quantified 21 years (1996–2016) of changes in the spatio-temporal dynamics of Accipiter hawks in Chicago, IL, USA. Using a multi-season occupancy model, we estimated Cooper's ( Accipiter cooperii ) and sharp-shinned ( A. striatus ) hawk occupancy dynamics as a function of tree canopy cover, impervious surface cover and prey availability. In the late 1990s, hawks occupied 26% of sites around Chicago, but after two decades, their occupancy fluctuated close to 67% of sites and they colonized increasingly urbanized areas. Once established, hawks persisted in areas with high levels of impervious surfaces as long as those areas supported high abundances of prey birds. Urban areas represent increasingly habitable environments for recovering predators, and understanding the precise urban features that drive colonization and persistence is important for wildlife conservation in an urbanizing world.

Investigating temporal and spatial correlates of the sharp decline of an urban exploiter bird in a large European city

“…This result is in agreement with studies from the United-Kingdom suggesting that the increase in Sparrowhawks in urban areas might be involved in the decline of local House Sparrow populations (Bell et al 2010). The Eurasian Sparrowhawk is indeed a major predator of House Sparrows (Anderson 2006;Bell et al 2010), especially near urban areas (Tinbergen 1946;Opdam 1979;Frimer 1989;Gotmark and Post 1996;Solonen 1997;Millon et al 2009;McCabe et al 2018). By preferentially predating on House Sparrows, Sparrowhawks are likely to have a direct negative effect on House Sparrow populations.…”

“…Several hypotheses have been suggested to explain the recent decline of House Sparrows. Among them, increasing inter-specific competition (Summers-Smith 2003, increasing predation rates (Eurasian Sparrowhawk, Accipiter nisus, Bell et al 2010;McCabe et al 2018), or the spread of diseases across species (Hartup et al 2001) may contribute to the observed decline. Moreover, this decline could also be linked to the emergence or intensification of pollution sources specific to cities: noise pollution (Meillère et al 2015a, b), light pollution (Dominoni et al 2013), air pollution Lehikoinen 1995, 1996;Llacuna et al 1996;Eeva et al 2009), or even electromagnetic radiations (Balmori and Hallberg 2007;Balmori 2009;Singh et al 2013).…”

Downtown Diet: a global meta-analysis of urbanization on consumption patterns of vertebrate predators

“…Fewer prey species in cities promotes higher population densities for those species that can exploit the urban environment (Steinberg et al, 1997;Uno et al, 2010). Such surges in prey population densities can in turn drive predator population increases, potentially fueling human-wildlife conflict (Yirga et al, 2017;Fleming, & Bateman, 2018;Mccabe et al, 2018).…”

“…Abundant prey species associated with urban environments such as brown rats (Rattus norvegicus), rock pigeons (Columba livia), and house mice (Mus musculus) could potentially be driving predation rates and protein (i.e. nitrogen) consumption, at least for mammalian and avian predators (Corsini et al;Newsome et al, 2010;Mccabe et al, 2018;Scholz et al, 2020). Our findings are contrary to an emerging hypothesis of relaxed predation phenomenon in urban areas, described by a meta-analysis of 25 studies that found predation rates on bird nests were reduced in urban areas (Eötvös et al, 2018).…”

“…If species richness in cities declines, the relative abundance of some common urban prey species can increase significantly. Therefore, we expect DEV to decrease in urban areas (Mccabe et al, 2018). We expect the urban predator trophic niche to reflect lower δ 15 N and greater δ 13 C ratios relative to their rural counterparts due to exploitation of anthropogenic food sources rich in corn, wheat, and sugar (Murray et al, 2015;Manlick, & Pauli, 2020;Scholz et al, 2020).…”