Differential effects of exotic predator-control on nest success of native and introduced birds in New Zealand.

The introduction of mammalian predators has been detrimental to many native birds in New Zealand. One solution to this problem has been the creation of "mainland islands" in which exotic predators are systematically removed. Although mainland islands have been effective in increasing some native bird populations, few studies have measured the effect of predator-control on nest success nor what effect control measures have on sympatric populations of introduced birds. We measured the effect of predator-control on nest survival rates in both native and introduced passerines in a mainland island near Kaikoura, New Zealand. Nest survival was significantly higher in Waimangarara Bush (the site with experimental predator-control) than in Kowhai Bush (the site with no predator-control) and this pattern was found in both groups of birds. However, mammalian predator-control increased nest success of native species significantly more than nest success of introduced species. This suggests that native birds benefit disproportionately from control of introduced predators, most likely because they lack behavioural defences against mammalian predators that are present among the introduced birds.