Decrypting the Breeding Biology of the Elusive and Declining Tahiti Petrel <i>Pseudobulweria rostrata</i>

Among procellariids, the Tahiti Petrel Pseudobulweria rostrata is one of the most endangered and least known species. Its global populations are declining, yet demographic and ecological studies remain scarce. Understanding the breeding cycle and behavior of Tahiti Petrel adults and chicks is essential to develop effective protection measures. To address this knowledge gap, Tahiti Petrel colonies of various sizes were studied at three sites in New Caledonia, with extensive sampling at two main sites and limited sampling at a third. A total of 157 burrows were monitored for up to two years using endoscopic cameras and camera traps. This allowed the depiction of the breeding phenology, reproductive success, frequency of adult nest visits, chick behavior, first emergence, and fledging dates. During the study, 75% of the identified burrows were visited by Tahiti Petrels. Egg-laying peaked in December but occurred year-round, indicating aseasonal breeding by Tahiti Petrels in New Caledonia. The average breeding cycle was 329 ± 11.6 days, including an average incubation period of 55.7 ± 0.9 days and an average chick-rearing period of 110.7 ± 5.6 days. Parents visited nests every 1.3 days on average during chick-rearing. After the chick’s first emergence, which typically occurred 31 days before fledging, adult visitation decreased. Chicks did not show defensive behavior against predators, and most chicks fledged after nine days without feeding. Breeding success was 50% at a predator-free site and 32% at a site with invasive predators. These findings suggest high sensitivity to disturbance and depredation, contributing to the species’ decline in New Caledonia and elsewhere in the world. Together with previous studies conducted in New Caledonia, these results provide crucial information for the implementation of adapted conservation measures for this declining species.