Movement Patterns of Hawaiian Petrels and Newell's Shearwaters on the Island of Hawai'i

Abstract

We studied movements and distribution and abundance of endangered Hawaiian Petrels ('Ua'u [Pterodroma sandwichensis Ridgway]) and threatened Newell's Shearwaters ('A'o [Puffinus auricularis newelli Henshaw]) on the island of Hawai'i in May-June 2001 and 2002. We recorded radar targets of either species at 14 of the 18 sites but recorded no birds visually at any site. Movement rates of petrels and shearwaters were very low (0-3.2 targets per hour) over all except one of the sites (Waipi'o Valley: 25.8 targets per hour). We saw radar targets moving from shortly after sunset throughout the rest of the sampling, suggesting that both petrels and shearwaters were present. Highest movement rates occurred 1-2 hr after sunset, when primarily Newell's Shearwaters are flying. Timing of evening movements suggests that Hawaiian Petrels fly over the northern and southern parts of the island and may dominate on Mauna Loa and Mauna Kea. In contrast, timing suggests that Newell's Shearwaters fly over essentially the entire island (except in the southwestern part, where no birds appear to occur), dominate numerically in the Kohala Mountains, and occur in low numbers on Mauna Loa, in the Puna District, and on the northern slopes of Mauna Kea. Evening flight directions were predominantly inland at all sites except four. The limited radar data suggest that a substantial population change did not occur in the Puna District from 1995 to 2001-2002.