Trial of burrow flaps to protect petrel chicks

Abstract

Burrow competition between the critically endangered Chatham petrel (Pterodroma axillaris) and the locally abundant broad-billed prion (Pachyptila vittata) is the main cause of Chatham petrel chick mortality, and in an unmanaged situation between 50% and 70% of chick deaths are due to burrow competition (Gardner & Wilson 1999). We have developed a simple, cheap neoprene flap that dissuades broad-billed prions from entering burrows but still allows Chatham petrels to enter their burrow (Sullivan 2000). This report describes a trial conducted on a more common analogue species, Pycroft's petrel (Pterodroma pycrofti) on Red Mercury Island. The flaps designed for use on Chatham petrel burrows were put in place shortly after the Pycroft's petrel chicks had hatched and they were left in place until the chicks had begun fledging. The report was designed to answer the following questions: Does installation of the burrow flap designed to deter prions from entering Chatham petrel burrows adversely affect breeding success in Pycroft's petrel burrows protected by a burrow flap?; Does the installation of the burrow flap affect feeding frequencies or fledgling weights of Pycroft's petrel chicks protected by a burrow flap? Pycroft's petrels were able to raise chicks with the burrow flap in place that was designed to protect Chatham petrels from interference from broad-billed prions. The adult birds probably took longer to enter burrows when they first encountered a burrow flap and some birds may have still taken longer than control birds to enter burrows six weeks after the flap was put in place. However, the data to support this assumption are limited and the extra few minutes taken are hardly of consequence given that foraging trips are of at least several days' duration.