Radar Study of Seabirds and Bats on Windward Hawai ' i

Modified marine surveillance radar was used to study the presence/ absence, abundance, and flight activity of four nocturnal species: Hawaiian darkrumped petrel [Pterodroma phaeopygia sandwichensis (Ridgeway)], Newell's shearwater [Puffinus auricularis newelli (Henshaw)], Band-rumped storm-petrel [Oceanodroma castro (Harcourt)), and Hawaiian hoary bat (Lasiurus cinereus semotus Sanborn & Crespo). Hawaiian seabirds were recorded flying to or from inland nesting colonies at seven sampling sites on the windward side of the island of Hawai'i. In total, 527 radar "targets" identified as petrel or shearwater-type on the basis of speed, flight behavior, and radar signal strength were observed during eight nights of sampling. Mean movement rates (targets per minute) for seabird targets were 0.1, 0.1,0.3, 3.8, 0.9, and 2.2 for surveys at Kahakai, Kapoho, Mauna Loa, Pali Uli, Pu 'ulena Crater, and Waipi '0 Valley, respectively. Two percent of the petrel and shearwater-type targets detected on radar were confirmed visually or aurally. Flight paths for seabird targets showed strong directionality at six sampling sites. Mean flight speed for seabird targets (n = 524) was 61 kmIhr for all survey areas. Peak detection times for seabirds were from 0430 to 0530 hours for birds flying to sea and 2000 to 2150 hours for birds returning to colonies. Most inland, lowelevation sampling sites could not be surveyed reliably for seabirds during the evening activity periods because of radar interference from insects and rapidly flying bats. At those inland sites predawn sampling was the best time for using radar to detect Hawaiian seabirds moving seaward. Hawaiian hoary bats were recorded at eight sampling sites. Eighty-six to 89 radar targets that exhibited erratic flight behavior were identified as "batlike" targets; 17% of these batlike radar targets were confirmed visually. Band-rumped storm-petrels were not identified during our surveys. THREE SPECIES OF SEABIRDS, Hawaiian darkrumped petrel (Pterodroma phaeopygia sandwichensis), Newell's shearwater (Puffinus auricularis newelli), Band-rumped storm-petrel (Oceanodroma castro), and Hawai'i's only endemic land mammal, the Hawaiian hoary bat (Lasiurus cinereus semotus), occur on the island of Hawai'i and appear on the State of Hawai'i Endangered Species List or Federal Endangered Species List (U.S. Fish and Wildlife Service 1992). Factors contributing to the decline of I Manuscript accepted 3 April 1996. 2 USGSIBRD (formerly National Biological Service), Pacific Islands Ecosystem Research Center, Hawai'i Field Station, P.O. Box 44, Hawai 'i National Park, Hawai 'i 96718. 3 Alaska Biological Research, Inc., P.O. Box 249, Forest Grove, Oregon 97116-0249. 4 Alaska Biological Research, Inc., P.O. Box 80410, Fairbanks, Alaska 99708-0410. 97 Hawai 'i's seabird populations include predation by introduced common barn owls (Tyto alba), cats (Felis catus), dogs (Canis familiaris), rats (Rattus norvegicus, R. rattus, and R. exulans), and mongooses (Herpestes auropunctatus) (Byrd and Moriarty 1981, U.S. Fish and Wildlife Service 1983, Simons 1985, Telfer 1986, Ainley et al. in press); decreased availability of areas suitable for nesting (U.S. Fish and Wildlife Service 1983, Reynolds et al. 1994b); and modified landscapes with structures and lighting that can attract birds and lead to collisions. The mortality of Hawaiian seabirds caused by bright lights and collisions with utility wires is well documented (Reed et al. 1985, Telfer et al. 1987, Cooper and Day 1994, Ainley et al. 1995). Threats to the Hawaiian hoary bat are largely unstudied; however, bat populations across the world are threat-