Burrow occupancy of broad-billed prions Pachyptila vittata on South East (Rangatira) Island, Chatham Islands, New Zealand

Abstract

Competition for breeding burrows between broad-billed prions (Pachyptila vittata) and other small burrowing seabirds on South East (Rangatira) Island, Chatham Islands, New Zealand is intense. This competition has a negative impact on the endangered Chatham petrel (Pterodroma axillaris) population. Competition is occurring in the broad-billed prion non-breeding season, a stage in the prion life cycle that we know nothing about. This study investigated the non-breeding period of a broad-billed prions life cycle on South East Island, information imperative to guide management decisions for future control or manipulation of the species. Seventy-seven broad-billed prion burrows were monitored nightly during parts of the 1996 and 1997 breeding seasons and the 1997 and 1998 non-breeding seasons to determine how often and which prions were using burrows. Of the 401 broad billed prions recorded in study burrows the majority (up to 76%) were not resighted in any subsequent season. Of prions using the same burrow over consecutive years, the greatest number were recaptured in the non-breeding season following the breeding season they had visited a burrow. Marginally fewer prions were recaptured in the non-breeding season following' the non-breeding season they had visited a burrow. Up to 10 broad-billed prions were recorded in individual burrows during the non-breeding season. A small number of broad-billed prions were recorded in more than one burrow. The majority of these multiple burrow visitors were found in burrows less then 5 metres away from the one they were banded in, but 24% were found in more distant burrows, a maximum of 100 metres away from the original banding point. Blockading, to prevent broad-billed prions from using selected burrows, lowered the use of these burrows in the subsequent non-breeding season. Broad-billed prion presence on South East Island was lower in the second year than in the first year of this study. It is suggested that broad billed prion occupation of South East Island may have been affected by El Nino-southern oscillation weather patterns in the second year of study.