Seabird Abstracts

Aircraft and vessel disturbances to Common Murres Uria aalge at

breeding colonies in central California, 1997-1999

Rojek NA, Parker MW, Carter HR & McChesney GJ (2007) Marine Ornithology 35:61-69

From 1997 to 199, we documented aircraft and vessel disturbances of Common Murres Uria aalge at three central California breeding colonies: Castle-Hurricane Colony Complex, Devil's Slide Rock, and Point Reyes. Most aircraft disturbances occurred when flyovers were <=305m above sea level. Helicopters tended to cause more disturbance than fixed-wing aircraft did, likely because of higher noise levels. At Castle-Hurricane, low aircraft flyovers occurred 49% and 656% more frequently than at Devil's Slide Rock and Point Reyes respectively. Flyovers also resulted in flushing of adult murres more frequently at Castle-Hurricane (31% of flyovers) and Point Reyes (25%) than at Devil's Slide (4%). Boat disturbance to murres also was substantially higher at Castle-Hurricane than at the other two colonies, resulting in lost eggs and chicks. Most boat disturbances occurred when vessels approached within 50m of active nesting areas and remained in the area for extended periods. The central California murre population declined extensively during the 1980s mainly because of mortality from gillnet fishing and oil spills. Although numbers increased at most colonies in the 1990s, the Castle-Hurricane Colony Complex only partly recovered - to about half of pre-decline numbers by 1997. Although population impacts are difficult to measure, disturbance effects area probably additive to impacts from continued mortality attributable to gillnet fishing and other factors that have led to slow recovery at this colony complex.

Keywords: Common Murre, Uria aalge, central California, aircraft, vessel, disturbance, alcid, colonial waterbirds, seabirds, Castle-Hurricane Colony Complex, Devil's Slide Rock, Point Reyes


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