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Survival and breeding success of the Osprey Pandion haliaetus in Sweden
Published online by Cambridge University Press: 11 May 2010
Summary
During 1942–1983, the average survival rate of Ospreys in Sweden (as derived from ringing data) was 53% during the first year, and for older birds it varied between 72% and 86% (below the level recorded in North America). The annual survival rate decreased significantly among young birds (1st-3rd years of life) but not among older age classes. A weak relationship between annual survival and rainfall in wintering areas in West Africa may exist for some year-classes.
Breeding success was 2.1 young per successful breeding attempt over the period 1961-1987, which is lower than during 1938-1946. The long-term annual growth rate of the population declined from 7% around 1940 to 5% around 1990.
A local decline in breeding success occurred during the 1960s and 1970s in areas heavily affected by acid precipitation in south-west Sweden, but this trend halted during the 1980s as liming programmes restored the fish stocks in acidified lakes. There was a significant relationship between lake productivity, measured as concentrations of total phosphorus, and breeding success: at 16 lakes breeding success ranged between 1.6 and 2.3 young per nest per year, and at the most oligotrophic lakes breeding success was close to the minimum required to balance mortality.
The Swedish population of the Osprey is not in acute danger, but the decline in the potential for population growth should be noted.
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- Copyright © Birdlife International 1994
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