Traits influencing range contraction in New Zealand's endemic forest birds.

Abstract

Understanding vulnerability of endemic taxa to predation is clearly important for conservation management. In New Zealand, predation by introduced mammals such as rats and mustelids is widely recognized as the primary factor responsible for declines of indigenous fauna. The aim of our study was to evaluate the vulnerability of New Zealand's surviving endemic forest bird species to impacts of introduced mammalian predators, and identify key life history attributes underlying this vulnerability. We measured range contraction following the introduction of exotic mammalian predators for 23 endemic forest bird species using information on both pre-human and current distributions. We used Bayesian modeling techniques to analyze whether variation in range contraction was associated with life history traits potentially influencing species' predation vulnerability, while accounting for phylogenetic relatedness. Our results showed that the extent of range contraction varied greatly among species, with some species remaining in available forest habitat throughout most of their pre-human range, and others having disappeared completely from the main islands. Cavity nesting was the key trait associated with more extensive range decline, suggesting that cavity-nesting species are more vulnerable to predation than species that nest in more open sites.