Environmental drivers of gadfly petrel vagrancy in the Southwest Pacific

Abstract

Seabirds are important indicators of ecological change. Their vulnerability to marine and terrestrial environmental disturbances is well documented, with seabirds now among the most threatened birds globally. Coupled with their capacity for far-ranging movements, incidences of vagrancy (individuals outside their regular, known geographical range) in seabirds can be a novel, early indicator of environmental change. We collated a comprehensive dataset of vagrancy in gadfly petrels (Pterodroma spp.) across the Southwest Pacific to investigate potential drivers of vagrancy in this group. Our dataset included 115 records of 10 taxa of Pacific-breeding gadfly petrel vagrants in the Southwest Pacific. Of these taxa, eight were more likely to occur as vagrants during neutral phases of the El Niño–Southern Oscillation and seven were less likely to occur during El Niño events. More directly, increasing poleward vagrancy in Collared P. brevipes, Kermadec P. neglecta and, potentially, White-necked Petrels P. cervicalis was associated with warmer-than-average sea-surface temperatures and may reflect expanded foraging ranges in response to ocean warming. Prospecting at potential breeding sites was recorded for 23% of vagrant records. This highlights the ecological plasticity necessary to establish new populations, providing potential opportunities for conservation support for population establishment, especially for threatened taxa. Our findings underscore the potential for vagrancy events to provide insight when assessing seabirds as indicators of environmental change.