Movement of the Hawaiian Petrel to Inland Breeding Sites on Maui Island, Hawai’i

Abstract

We studied nightly movement rates, behavior, flight directions, and flight altitudes of Hawaiian Petrel (Pterodroma sandwichensis) and possibly Newell’s Shearwater (Puffinus auricularis) at 15 sites on Maui, Hawaiian Islands, in June 2001. We observed no Newell’s Shearwaters visually, but saw Hawaiian Petrels at all of the nine sites around eastern Maui and at two of the six sites around western Maui. Mean nightly movement rates on radar generally were higher in eastern Maui than western Maui, although movement rates in the northeastern part of western Maui were comparable to those at several sites in eastern Maui. The highest movement rates occurred at the Ke’anae Valley, Mokuia Point, Nu’u Bay, and Kaupo sites, all of which are located on the northeastern or southeastern slopes of Haleakala in eastern Maui. Hawaiian Petrels (identified visually) flew inland primarily between 10 min after sunset and the point of complete darkness (about 30 min after sunset), with no movements observed beyond 50 min after sunset. Radar movements peaked just before the point of complete darkness, but a substantial number of radar targets also flew inland at 30-50 min after sunset, with some movement occurring even after that period. These later movements suggest that small numbers of Newell’s Shearwaters are flying inland at several locations. Further, there was a higher proportion of these late flights in western Maui than in eastern Maui, suggesting that Newell’s Shearwaters, if present, form a higher proportion of the two species in western Maui than in eastern Maui. Mean flight directions at all sites were in an inland direction, with little variation in flight directions at most sites. Mean flight altitudes of the Hawaiian Petrel were 190 m above ground level, similar to those at Kaua’i Island. The data suggest that the number of Hawaiian Petrels on Maui may be higher than the current estimate of 1,800 birds.