Comparison of predation by two suburban cats in New Zealand

Abstract

AbstractTo study the effects domestic cats may have on surrounding wildlife, a complete list was made of 558 items caught in the garden or brought into the house by one cat over 17 years, from 1988 to 2005. The effect on prey populations was assessed by comparing their abundance with the previous 15 years’ population without a cat. On balance, this cat (Cat 1) was clearly beneficial to the native bird species by killing rodents and deterring mustelids. The diet of a second cat (Cat 2) was recorded in the same way from 2006 to 2016. This cat caught half the number of items 148:287, but in the same proportions: house mice (37.8:42.6); ship rats (12.8:12.1); European rabbits (all young) (8.1:6.7); weasels (0.7:0.4); dunnock (12.8:9.2); house sparrow (2.0:3.1); blackbird (2.7:2.5); song thrush (1.4:1.3); European greenfinch (0.7:5.8); chaffinch (0.7:3.3); silvereye (10.1:8.3); New Zealand fantail (2.0:1.0); lizards (8.1:1.7). Despite this, there were significant differences: Cat 2 avoided finches (2:28, P = 0.004), and took a few more lizards (12:5). For both cats, birds apparently formed about a third of their diet: 33.4% and 34.5%, but comparison of the proportion of birds and rodents brought into the house (12:92) and found dead away from the house (49:45) implies that 320 rodent kills may have been missed, being far more difficult to find. As top predators, these cats were clearly beneficial to native birds, and proposed control or elimination may precipitate mesopredator release and a rabbit problem.