Editor's Choice: Seasonal mortality and sequential density dependence in a migratory bird

Submitted by Johan on 28 July 2015.

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This study compares annual survival patterns of red knots Calidris canutus islandica between two periods, when winter food at the Wadden Sea was reduced by cockle harvesting and in following years when cockle-dredging was stopped.

As expected, winter survival was reduced during the years with food reduction and post-winter population size declined. However, the survival during the remaining part of the year increased in comparison with survival during the relaxation period (without cockle-dredging). This is interpreted as a case of density-dependent reduction in winter survival caused by food shortage because of the cockle-dredging, followed by density dependent increase in survival during the following summer period due to the reduced post-winter population density. In the years after cockle-dredging winter survival increased and summer survival decrease to reach a similar survival rate throughout the year. This is an interesting case study in the field of limiting and regulating population effects among migratory animals in seasonal environments, where much remains to be understood about the population dynamics.


Thomas Alerstam, Editor in Chief

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Editor´s Choice