Patterns of range contraction in native New Zealand passerine birds

Abstract

Two successive waves of human impacts have been associated with the colonisation of New Zealand, resulting in widespread contractions of avian species' ranges. However, variation exists in the amount of range contraction faced by different species, and also the number of species lost per region. The aim of this study was to identify factors underlying this variation by studying patterns of range contraction in 20 native New Zealand passerine species. Data was collected on the distribution of these species in 75 Ecological Regions of New Zealand using subfossil records (indicating presence pre-human or during Maori occupation), historical European records (indicating presence at some stage during European occupation) and present records.

From these data the contraction of species from regions was determined during the two periods of human occupation of New Zealand (Maori and European), and statistical models were developed to identify: (1) what regional features were associated with range contraction, and (2) what life-history traits were associated with range contraction, during both Maori and European occupation.

The strongest predictor of range contraction during Maori occupation, was the extent of deforestation. During European occupation, range contraction was associated with 1880 European population density, which may indicate the effect of higher introduced predator densities in these regions. Species with the largest range contractions during Maori occupation possessed large body masses, relating to slow reproductive rates. During European occupation, species with poor flight ability and long incubation periods were associated with range contractions, traits increasing a species vulnerability to introduced predators. These results suggest that the patterns of range contraction reflect the different impacts operating in each occupation period, and the differential susceptibility of species to those impacts. The implications of these results for conservation management are discussed.