Quantifying the benefits of long-term integrated pest control for forest bird populations in a New Zealand temperate rainforest

The control of introduced mammalian predators has become a standard response to protecting the viability of threatened wildlife species on oceanic islands. However, examples of successful outcomes of integrated pest control in forests are few. We investigated the efficacy of a pest control programme in the Landsborough Valley, New Zealand, during 1998–2009, which used continuous trapping to control mustelids and pulsed aerial application of the toxin 1080 to control rats (Rattus spp.) and brushtail possums (Trichosurus vulpecula). We predicted recovery in the populations of mohua (Mohoua ochrocephala) and other predator-sensitive hole-nesting birds and maintenance of numbers of South Island kaka (Nestor meridionalis meridionalis). In addition, we examined whether annual mean counts of mohua and kaka, as potential ‘population indicator species’, could predict those of other forest bird species. Annual counts of nine species (eight indigenous: bellbird Anthornis melanura, brown creeper Mohoua novaeseelandiae, fantail Rhipidura fuliginosa, grey warbler Gerygone igata, mohua, rifleman Acanthisitta chloris, tui Prosthemadera novaeseelandiae and yellow-crowned parakeet Cyanoramphus auriceps; one introduced: song thrush Turdus philomelos) showed significant increases during the 12-year study period. South Island kaka and redpoll (Carduelis flammea) showed no change with time. In general, trends in the two focal threatened taxa (mohua and kaka) were poor predictors of trends in other bird species. Lack of correlation in annual counts between bird species that share a recovery trajectory are likely due to differences in breeding biology and resource use. Our results suggest that an integrated strategy for predator management is effective at mitigating the impacts of predation by introduced mammals on forest birds, including the most vulnerable species, at a landscape scale.