Seasonal variation in reproductive success and post-nuptial moult of blue tits in southern Europe: an experimental study |
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Authors: | Juan José Sanz |
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Institution: | (1) Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), José Gutierrez Abascal 2, E-28006 Madrid, Spain e-mail: sanz@mncn.csic.es, ES |
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Abstract: | Post-nuptial moult and reproductive success were studied in relation to timing of breeding in blue tits, Parus caeruleus, breeding in southern Europe. A group of experimentally delayed pairs was created by removing first clutches, thereby inducing
late repeat clutches. Reproductive success and post-nuptial moult of delayed pairs were compared with both control pairs that
bred early and unmanipulated late-breeding pairs. Delayed pairs fledged fewer young and with a lower body mass than control
pairs. However, the number of fledged young and fledgling mass did not differ between delayed and late-breeding pairs. These
results were more consistent with the date hypothesis, and it is concluded that the timing of breeding and reproductive success
may be causally related in the blue tit. This study reveals a harmful effect of relaying on female body mass at the end of
the nestling period. Therefore, females apparently pay the costs of relaying, since a reduction in body mass during the nestling
period may be accompanied by a lowered survival probability. Delayed and late-breeding males often began moulting while still
feeding young, but neither control males nor females from the three study groups did so. These results support the view that
timing-related energy constraints on breeding may be important causes of a seasonal decline in reproductive success at different
latitudes.
Received: 15 March 1999 / Accepted: 19 July 1999 |
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Keywords: | Blue tit Southern latitude Moult-breeding overlap Parus caeruleus Reproductive success |
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