This study investigated the potential for non-native grey squirrels (Sciurus carolinensis) to compete with birds at supplementary feeding stations. Whilst it is commonly assumed that the non-native Grey Squirrel provides interference competition, excluding birds from feeders, empirical evidence of this is currently unavailable.
By placing models of Grey Squirrels at supplementary feeding stations, this study demonstrates that their presence can reduce bird use.
It reveals that total bird resource use was reduced by 98% and most species showed similar sensitivities. The likelihood and magnitude of interference competition depended on how rapidly displaced birds found alternative food sources; it was greatest where there were high Grey Squirrel densities and few supplementary feeders.
Colin Bonnington, Kevin J. Gaston and Karl L. Evans, 2014, Assessing the potential for Grey Squirrels Sciurus carolinensis to compete with birds at supplementary feeding stations, Ibis 156, 220–226