Assessing the potential for Grey Squirrels Sciurus carolinensis to compete with birds at supplementary feeding stations

Abstract

Supplementary feeding of birds, particularly in urban areas, is often associated with increased population size and fecundity. In the UK, the non‐native Grey Squirrel Sciurus carolinensis is common in rural and urban habitats. It exploits supplementary feeders and may induce interference competition by excluding birds, but empirical evidence of this is unavailable. Using controlled model presentation experiments, we demonstrate that Grey Squirrels could reduce bird use of supplementary feeders and induce interference competition. Total bird resource use was reduced by 98% and most species exhibited similar sensitivities. The likelihood and magnitude of interference competition will depend on how rapidly displaced birds find alternative food sources; it will be greatest where there are high Grey Squirrel densities and few supplementary feeders. Other studies suggest that supplementary feeding increases Grey Squirrel numbers, and the species is also predicted to expand its non‐native range across most of Europe. Our data indicate that Grey Squirrels may eventually alter the net effect of supplementary feeding on bird populations across the European continent; increased use of squirrel‐proof feeders may help to minimize such effects.

Supplementing non‐target taxa: bird feeding alters the local distribution of mammals

“…At sites where mammals have direct access to food, direct competition for resources can reduce the benefits of supplemental feeding. One recent study found that interference competition with gray squirrels reduced the ability of birds to access supplemental food by upwards of 98% (Bonnington et al 2014). In another supplemental feeding initiative targeting gamebirds in England, non-target taxa accounted for 54% of feeder visits with mammals consuming upwards of 67% of the food provided (S anchez-Garc ıa et al 2015).…”

Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds

“…Grey Squirrels carry disease (squirrelpox, Bruemmer et al 2010; Borrelia burgdorferi, the agent of Lyme disease, Millins et al, 2015, Millins et al, 2016, and cause economic losses in forestry (Mayle and Broome, 2013). In the context of this work, evidence suggests that urban Grey Squirrel population size and density is associated with the provision of supplementary food in gardens (Bowers and Breland, 1996;Parker and Nilon, 2008) and there is some evidence that they can competitively exclude birds at supplementary feeders (Hewson et al, 2004;Bonnington et al, 2014a). Bonnington et al (2014a) used taxidermied Grey Squirrels on feeders, and showed that resource use by birds was reduced by 98% in the presence of a mounted animal.…”

“…In the context of this work, evidence suggests that urban Grey Squirrel population size and density is associated with the provision of supplementary food in gardens (Bowers and Breland, 1996;Parker and Nilon, 2008) and there is some evidence that they can competitively exclude birds at supplementary feeders (Hewson et al, 2004;Bonnington et al, 2014a). Bonnington et al (2014a) used taxidermied Grey Squirrels on feeders, and showed that resource use by birds was reduced by 98% in the presence of a mounted animal. However, we have no quantitative data on how the presence of live Grey Squirrels affects feeder usage by garden birds, nor how much of the food provided is taken by the squirrels.…”

“…Typically, standard feeders are surrounded by guards to prevent access by squirrels and other large species such as corvids and invasive parakeets (Antonov and Atanasova, 2003;Sorace and Gustin, 2009). Such guards should decrease the food taken by Grey Squirrels and thus their negative impact on supplementary feeder usage by target birds (Bonnington et al, 2014a;Hanmer et al, 2017a). Furthermore, if the presence of Grey Squirrels reduces resource intake rates by birds (Bonnington et al, 2014a), we may expect to see a behavioural response to their presence.…”

Jewels for Dollars: Native and Nonnative Freshwater Fish Interactions in a Stressful Dry Down Environment

“…Interspecific competition will occur among species that share the same requirements (i.e., occupying similar niches), and those with superior competitive abilities will outcompete others (Dayan and Simberloff 2005;Weiner 1990;Connell 1983;Schoener 1983). Nonnative competitors have been shown to negatively affect native species through displacement from preferred habitats Brooks and Jordan 2010) and preferred food resources (Bonnington, Gaston and Evans 2014). However, the effects of competition can be difficult to quantify (Tylianakis 2008;White et al 2006).…”