Feeding frequency, meal size and chick growth in the threatened Pycroft's petrel (Pterodroma pycrofti)

Abstract

Many species of gadfly petrel (genus Pterodroma) are threatened or endangered, including, in New Zealand, the Chatham petrel (Pterodroma axillaris), and Pycroft's petrel (P. pycrofti). Conservation actions for these species include the establishment of new breeding colonies on predator-free offshore islands by translocation. Due to the high philopatry of most gadfly petrels, only chicks that have not yet been imprinted with their natal ground can be transferred. Translocation of Chatham petrel and Pycroft's petrel chicks are scheduled in 2002. However, data on the chick stage in these two species, and in small Pterodroma in general, are scant, and techniques to age chicks to determine their transferability are needed. The purpose of this study was to examine the feeding frequency, meal size and growth of Pycroft's petrel nestlings, to compare the results with Chatham petrel data and to identify factors that could be used to age a chick of unknown age prior to a translocation. Fifty Pycroft's petrel chicks were monitored between 17 January and 26 March 2001 on Red Mercury Island, New Zealand. Chicks were weighed every one or two days to determine their feeding frequency and meal size, and had their bill, tarsus, tail and wing length measured at regular intervals until they fledged or until 26 March. Thirty other chicks formed a control group and were weighed and measured on 29 January and 15 March. The age of first emergence from burrow was also determined. Similar data on Chatham petrel were also analysed.