11 research outputs found
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Reproductive performance of seabirds: the importance of population and colony size.
Compared reproductive performance of 5 species of seabirds at St. George Island (2.5 million birds) and St. Paul Island (250 000 birds), in the SE Bering Sea. All species had lower chick growth rates at the larger colony; differences were statistically significant in 4 species. Fledge weights of common murres Uria aalge on St. George Island were 84-88% of those on St. Paul. Average fledge weights of thick-billed murres U. lomvia on St. George were only 74% of those for chicks from St. Paul. No significant differences were found in clutch size or breeding success between populations breeding at the 2 colonies. For black-legged kittiwakes Rissa tridactyla common murres, and thick-billed murres, analysis was extended to include published data from other colonies. There were consistently negative relationships between population size and several measures of breeding performance (clutch size, growth rate, fledge weight, and breeding success). In addition to the lower breeding success at colonies that support large populations, chicks from these colonies may be subject to higher postfledging mortality because of fledging at lower weights.-from Author
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Foraging radii and energetics of least auklets (Aethia pusilla) breeding on three Bering Sea Islands
The authors studied the relationship between the foraging radius and energy economy of A. pusilla breeding in colonies on three islands in the Bering Sea (St Lawrence, St Matthew, and St George Islands). The distance to which auklets commuted on foraging trips varied by more than an order of magnitude c5-56 km), but mean field metabolic rate did not vary significantly among birds from the three islands. The authors modeled the partitioning of energy to various activities and hypothesized that the added cost of commuting incurred by auklets from St Lawrence Island (foraging radius, 56 km) was offset by reduced energy costs while foraging at sea. Data indicated that auklets from St Lawrence Island fed on larger, more energy-rich copepods than auklets from St Matthew Island (foraging radius, 5 km). -from Author
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Breeding biology of the Xantus' murrelet.
Synthliboramphus hypoleucus were studied on Santa Barbara Island, California. Clutch initiation occurred from March-June and usually peaked in April. The 2-egg clutch was 45% of the female's weight. Eggs were laid eight days apart. Both sexes shared duties during a 34-day incubation period; partners relieved one another every 3-4 days. Eggs were typically left unattended in the interval between laying of successive eggs, immediately after clutch completion, and sporadically during incubation. Breeders and non-breeders of both sexes followed similar patterns of weight change, reflecting similar patterns of colony attendance; murrelets lost weight after the egg-laying period, then gradually gained weight through the rest of the breeding season. The downy young left the nest two nights after hatching, unfed and weighing <30 g. Chicks and their parents apparently moved well offshore their first night at sea. Even though most murrelets on Santa Barbara nested in concealed rock crevices, irregular nest attendance patterns left eggs vulnerable to predation, resulting in the loss of 44% of the eggs laid. Predation by deer mice Peromyscus maniculatus is currently the greatest risk to breeding.-from Author
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Breeding biology of the Xantus' murrelet.
Synthliboramphus hypoleucus were studied on Santa Barbara Island, California. Clutch initiation occurred from March-June and usually peaked in April. The 2-egg clutch was 45% of the female's weight. Eggs were laid eight days apart. Both sexes shared duties during a 34-day incubation period; partners relieved one another every 3-4 days. Eggs were typically left unattended in the interval between laying of successive eggs, immediately after clutch completion, and sporadically during incubation. Breeders and non-breeders of both sexes followed similar patterns of weight change, reflecting similar patterns of colony attendance; murrelets lost weight after the egg-laying period, then gradually gained weight through the rest of the breeding season. The downy young left the nest two nights after hatching, unfed and weighing <30 g. Chicks and their parents apparently moved well offshore their first night at sea. Even though most murrelets on Santa Barbara nested in concealed rock crevices, irregular nest attendance patterns left eggs vulnerable to predation, resulting in the loss of 44% of the eggs laid. Predation by deer mice Peromyscus maniculatus is currently the greatest risk to breeding.-from Author