Nest-site use by an introduced parrot in New Zealand

Abstract

Invasive birds that nest in cavities can monopolise cavity resources and limit breeding opportunities for cavity-breeding native species. Robust ecological information on the factors influencing selection and patterns of use of nesting sites, and a comprehensive multi-scale framework for the collection and analysis of nesting data, are essential for assessing the effects of introduced cavity nesters on communities of native cavity nesters. The native avifauna of New Zealand lacks primary cavity-excavators, and is now host to a suite of introduced cavity-nesting birds that may compete for suitable nesting sites. For most of these introduced species, however, data on nesting-site use are lacking. We studied the nesting ecology of the most successful psittacine invader, the Eastern Rosella (Platycercus eximius), in the North Island. Rosella nest-site use was investigated at the microhabitat, macrohabitat, and landscape scales. The number of potential nesting sites available in an area and proximity to fresh water were important determinants of occupancy of nest sites by Rosellas. In urban areas where mature, cavity-bearing trees were rare, Rosellas were observed using alternative nesting sites in tree ferns. This apparent flexibility in nesting behaviour may have contributed to the success and spread of Eastern Rosellas within New Zealand.