Why do Bulwer’s Petrels Bulweria bulwerii change nest?
Owning a nest is a prerequisite for breeding in Procellariiform seabirds, which can leave their single egg and/or chick unattended for long periods and show high nest fidelity. However, the determinants of nest fidelity vary among species. Amongst them, Bulwer’s Petrel Bulweria bulwerii lays the biggest egg relative to body size within the Family Procellariidae. Therefore, individuals should choose their nests carefully and change essentially if they can improve their reproductive performances. This study conducted on Vila islet, Azores, aimed to determine why Bulwer’s Petrels actually change nest. Nest fidelity exceeded 85%. Nest changes were most likely to occur after a breeding failure or a non-breeding year, but they did not allow improving breeding success and they often resulted in missed breeding years. On average, the new nests were not of higher quality than the old ones, except for the individuals whose first breeding attempt in the new nest was successful. In addition, the quality of the new nest was unrelated to the number of skipped years and to the distance moved. Almost half of changes occurred towards neighbouring nests. They were associated with a lower probability to skip years. Therefore Bulwer’s Petrels might prioritize proximity over nest quality to reduce the costs of nest changes.