engleski

Intra-seasonal changes in reproductive strategy of a multi brooded passerine: the tree sparrow, Passer montanus

Birds apply different strategies to maximize the number of offspring that they can produce and rear within a breeding season. In order to evaluate how a multi-brooded bird species adapts its breeding strategy during the breeding season, we investigated variations in clutch size, egg traits and sex of the final eggs in a population of the tree sparrow Passer montanus, in north-western Croatia. Our results show that females invest most resources in the second clutch of the season, whereas investment in the first and the last clutch is reduced. Furthermore, we show that females follow “brood survivor strategy” for their second clutches, but not for the first and the third clutch. There is also indication that females tend to produce more sons in the final eggs when resources are abundant and more daughters when they are limited. The potential value of these reproductive strategies is discussed with regard to offspring sex and changing environment over the course of the season.

reproductive strategy; egg traits; sex ratio; multi-brooded passerine; tree sparrow; Passer montanus

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