Ardea
Official journal of the Netherlands Ornithologists' Union

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Danchin E. & Monnat J.Y. (1992) Population-dynamics modeling of two neighbouring Kittiwake Rissa tridactyla colonies. ARDEA 80 (1): 171-180
Capture-mark-recapture models and Leslie matrix models were used to estimate annual adult survival rates and the demographic balance in a flourishing (annual increase 41%) and in a nearby declining Kittiwake Rissa tridactyla colony (annual decrease 15%). Age at first breeding attempt and adult survival rate did not differ much between the two colonies. However, breeding success was highest in the flourishing colony. The Leslie matrix model showed that the differences in fecundity could explain only a small part of the demographic trends. Moreover, adults breeding in the flourishing colony were more faithful in later years and young born in the flourishing colony were more philopatric when sexually mature. The flourishing colony also attracted more young from other colonies than the declining colony, and the proportion of adults that bred was higher. Observations of marked birds indicated that adults and young actually migrated from the declining colony into the flourishing colony, the movements probably being caused by egg predation by Ravens Corvus corax and by the presence of ticks in the declining colony. The study shows that even in species that are known for their faithfulness to the breeding colony, breeding birds can move to other colonies when the environment becomes unfavourable.


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