Distribution of Xantus' Murrelet Synthliboramphus hypoleucus at sea in the Southern California Bight, 1995–97 |
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| Authors: | DARRELL L. WHITWORTH JOHN Y. TAKEKAWA HARRY R. CARTER SCOTT H. NEWMAN THOMAS W. KEENEY PAUL R. KELLY |
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| Affiliation: | US Geological Survey, Biological Resources Division, Western Ecological Research Center, San Francisco Bay Estuary Field Station, PO Box 2012, Vallejo, California 94592, USA;US Geological Survey, Biological Resources Division, Western Ecological Research Center, Dixon Field Station, 6924 Tremont Rd, Dixon, California 95620, USA &Department of Wildlife, Humboldt State University, Arcata, California 95521, USA;Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, California 95616, USA;Environmental Division, Naval Air Weapons Station, Point Mugu, California 93042, USA;California Department of Fish and Game, Office of Oil Spill Prevention and Response, 1700 'K' St, PO Box 944209, Sacramento, California 94244, USA |
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| Abstract: | We radiomarked 153 Xantus' Murrelets Synthliboramphus hypoleucus captured at sea near Santa Barbara Island (SBI), the largest murrelet colony in the California Channel Islands, USA. We tracked these radiomarked murrelets in the Southern California Bight (SCB) off coastal southern California during the 1995-97 breeding seasons. In 1995 during mild El Niño conditions, the murrelets were distributed in non-upwelling areas. In 1996-97, they were distributed in dense patches, aggregating in cool upwelled waters near the northern Channel Islands or south of San Nicolas Island. Murrelets flew longer distances from SBI to foraging areas in 1997 (̄= 111 ± 44 km) than in 1996 (̄= 62 ± 25 km), but the distances they travelled did not differ between months (Apr and May) within years. Mean foraging distances from SBI were similar for 'incubating' murrelets (determined on the basis of repeated visits to SBI) and 'non-incubating' murrelets during the colony attendance period. We attributed the low return rate of radiomarked murrelets to SBI to the capture and marking of a large proportion of birds that were not actively incubating rather than to any adverse effects of radio attachment. We believe changes in murrelet foraging patterns between the 1970s and 1990s are associated with changes in prey resources in the SCB. Flexibility in the foraging strategies of these murrelets may be related to the highly variable marine environment at the southern end of the California Current Up welling System. |
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