Patterns of Movement of Dark-Rumped Petrels and Newell's Shearwaters on Kauai

We used ornithological radar and night-vision scopes to study movement patterns of Dark-rumped Petrels (Pterodroma phaeopygia sandwichensis) and Newell's Shearwaters (Puffinus auricularis newelli) on the island of Kauai, Hawaii, from 1992 to 1994. Movement rates on radar (targets/hr) for both species peaked for ∼2 hr around sunset and sunrise and were low in the middle of the night. Dark-rumped Petrels generally moved during crepuscular periods, whereas Newell's Shearwaters were strongly nocturnal. Movement rates were much higher in fall 1993 than in fall 1992, probably because of effects of Hurricane Iniki in 1992, and were higher in summer than in fall, probably because of the presence of nonbreeding birds in summer. Movement rates increased through time in summer, probably because numbers of nonbreeding birds visiting colonies increased through time, but declined through time in fall because fewer adults returned to the colony as fledging progressed. Effects of the moon on movement rates appeared to be small. Movement rates varied geographically, generally being much higher on eastern and northern Kauai than on southern Kauai. Movements were predominantly inland in the evening, predominantly seaward in the morning, and both directions in the middle of the night. Birds flew between 8 and 800 m above ground level (agl) and averaged 142 m agl for all procellariid species combined. There was no relationship between elevation of a site and flight altitude of birds at that site. Flight altitudes at a site generally were highest during the evening peak of movement and lowest during the morning peak in summer but were not different among three periods of the night in fall. Dark-rumped Petrels flew at significantly higher altitudes than did Newell's Shearwaters in fall 1993 and summer 1994 but not in summer 1993.