Fearing the feline: domestic cats reduce avian fecundity through trait‐mediated indirect effects that increase nest predation by other species

Abstract

Summary1. Urban areas contain high densities of non-native species, which in the UK include the domestic cat Felis catus (Linnaeus 1758) and the grey squirrel Sciurus carolinensis (Gmelin 1788). The direct predation effects of domestic cats on prey populations attract intense debate, and such influences of the nest-predatory grey squirrel are receiving increasing attention. In contrast, theory predicts that sublethal and indirect effects are more important, but empirical evidence is currently lacking. 2. We conducted controlled model presentation experiments at active urban blackbird Turdus merula (Linnaeus 1758) nests to provide the first empirical evidence that quantifies the potential sublethal and indirect effects of predators (domestic cat and grey squirrel) on avian reproductive success. 3. Domestic cat models reduced subsequent parental provisioning rates, a strong indicator of sublethal effects, by one-third relative to a nonpredatory rabbit Oryctolagus cuniculus (Linnaeus 1758) control. There was no compensatory increase in food load size. Previous experiments demonstrate that this magnitude of reduced food delivery will reduce nestling growth rates by c. 40%. The grey squirrel model induced similar but weaker effects. 4. Following the brief presence of the domestic cat model, subsequent daily nest predation rates, chiefly by corvids, increased by an order of magnitude relative to the squirrel and rabbit models. The intensity of parental nest defence elicited in response to model presentations predicts the probability of such third-party predator predation events, and the domestic cat model generated significant increases in nest defence behaviour. 5. Synthesis and applications. The brief presence of a domestic cat at avian nest sites reduces subsequent provisioning rates and induces lethal trait-mediated indirect effects. We provide the first robust evidence for these latter effects in any avian predator-prey system, although they are likely to be common in many avian assemblages with high predator densities. It is imperative that future assessments of the impact of predatory species on avian prey species take lethal trait-mediated indirect effects into account, as so doing will prevent biased estimates of predator effects and facilitate the design of more effective control strategies. Full mitigation of the sublethal and indirect effects of domestic cats would problematically require permanent indoor housing.

Assessing the effectiveness of the Birdsbesafe® anti-predation collar cover in reducing predation on wildlife by pet cats in Western Australia

“…Bonnington et al (2013) found that parental provisioning rates in birds were reduced by one third following exposure to a cat model, which could reduce nestling growth rates by 40%. Furthermore, the presence of the cat model for only 15 min at the nest significantly increased the chances of nest predation over the next 24 h by corvids detecting increases in alarm calls.…”

“…Even the presence of pet cats may alter prey behaviour, contributing to population declines (Beckerman et al, 2007;Bonnington et al, 2013). Other authors argue that pet cats hunt common species that cope with the impacts or take diseased or injured individuals, with the focus on cats deflecting attention from more significant causes of wildlife decline (Fitzgerald, 1990;Fitzgerald and Turner, 2000;Sims et al, 2008;Shochat et al, 2010;Siracusa, 2012).…”

Annual variation in prey composition of domestic cats in rural and urban environment

“…As a result, cats can efficiently compete with wild predators (Krauze-Gryz et al 2012b). Urban and suburban cats mainly focus on birds, which results in serious predation rates (Lepczyk et al 2004) or increases in sub-lethal factors, such as a reduction in fecundity (Beckerman et al 2007) or food delivery to chicks (Bonnington et al 2013). Special attention should be paid to the influence of house cats on the fauna of nature reserves located in or adjacent to cities or suburbs as the presence of free-ranging domestic cats, which are likely the most abundant predator, can reduce the effectiveness of these protected areas as a tool for protecting nature (Wierzbowska et al 2012).…”

“…Consequently, many conservation initiatives have been aimed at the eradication of feral cats on islands (Nogales et al 2004), but the threat that free-ranging house cats pose to wildlife is also serious and has gained recognition by both researchers and conservationists (e.g., Kays and DeWan 2004;Baker et al 2005;Sims et al 2008;Morgan et al 2009;Bonnington et al 2013). While there is a set of mitigation measures that can be considered (reviewed in Calver et al 2011), the application of any of them requires cooperation with cat owners, who often fail to understand the detrimental effect their pets can have on wildlife (McDonald et al 2015).…”

Ranging characteristics of the domestic cat (Felis catus) in an urban environment

“…Although the numbers and diversity of prey taken by pet cats have been widely investigated (Churcher and Lawton 1987;Barratt 1997bBarratt , 1998Robertson 1998;Woods et al 2003;Baker et al 2005Baker et al , 2008van Heezik et al 2010;Thomas et al 2012;Loyd et al 2013) the degree to which they may be negatively affecting wildlife populations in urban settings is still equivocal (Crooks and Soulé 1999;Lilith et al 2010). Furthermore, while most studies have considered the direct effects of cat predation, other studies have emphasised the potential negative indirect consequences of domestic cats (Beckerman et al 2007;Bonnington et al 2013), further depressing prey numbers in areas with high cat densities.…”