Post-fledging distribution of 'ua'u (Hawaiian petrel Pterodroma sandwichensis) from Kaua'i, Hawai'i and effectiveness of rehabilitation

The 'ua'u (Hawaiian petrel Pterodroma sandwichensis) is an Endangered seabird endemic to the Hawaiian Islands. The at-sea distribution of this species is an under-studied aspect of its ecology. We tracked 10 petrels fledging from the island of Kaua'i to their first wintering grounds, an area which has not previously been described. We also compare birds fledging naturally from their burrows with birds that were grounded by light attraction, rehabilitated, and released. All fledglings travelled over 2000 km southwest after leaving Kaua'i until they reached the Inter-Tropical Convergence Zone and the frontal zone that separates the westward-flowing North Equatorial Current from the eastward-flowing North Equatorial Counter Current. At this point, birds still transmitting turned west, passing through Micronesia before eventually reaching the Philippines. Three birds entered the Lagonoy Gulf in the Philippines, 2 birds briefly entered the South China Sea and the waters off Taiwan, and 1 bird flew up to Japan before returning to the waters off the Philippines. The core use area within the wintering ground was characterized by higher temperatures, lower sea level anomaly, and higher chlorophyll a concentrations. While wild fledglings transmitted longer than rehabilitated birds, this was only weakly significant, and the fact that several rehabilitated birds made it to their first wintering grounds highlights the importance of rescue and rehabilitation efforts. The potential threats to birds over-wintering in this area include concentrated fishing activity in the Lagonoy Gulf, nocturnal squid fishing vessels across the region, marine pollution, and the impacts of climate change to the region's marine environment.