Responses of New Zealand forest birds to management of introduced mammals.

Abstract

Over the past 1000 years New Zealand has lost 40-50% of its bird species, with over half of the extinctions attributed to predation by introduced mammals. Populations of many extant forest bird species continue to be depredated by mammals, especially rats, possums and mustelids. The management history of New Zealand's forests over the past fifty years presents a unique opportunity in which a varied and sustained programme of mammalian predator control has created a broad-scale replicated management experiment. We present here a meta-analysis of population-level responses of forest birds to different levels of mammal control recorded across the breadth of New Zealand. We collected data from 32 uniquely treated sites and 20 extant bird species representing a total of 247 population responses to three intensities of invasive mammal control (zero, low and high intensity). The treatments varied from eradication of invasive mammals via ground-based techniques, to periodic suppression of mammals via aerially-sown toxin. We modelled population-level responses of birds according to key life history attributes in order to understand the biological processes that influence species' responses to management. Larger endemic species, such as the Kaka and New Zealand Pigeon, regularly showed positive population-level responses to mammal control. We also identified one small species of shallow endemism (the Fantail), and four non-endemic species (the Blackbird, Chaffinch, Dunnock and Silvereye) that arrived in New Zealand in the last 200 years, that tend to decline in detections after mammal control. Our study suggests that large, deeply endemic forest birds, especially those that nest in cavities, are the species most at risk of further decline in the absence of mammal control, and conversely, reveals five species that apparently tolerate the presence of invasive mammals and whose populations may be sensitive to competition from larger endemic birds. Article impact statement: Management of introduced mammals across New Zealand has preferentially benefited large and endemic forest birds. This article is protected by copyright. All rights reserved.