| department of population ecology | ::: | institute | ::: | university | ::: |  |
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dr hab. Mariusz Cichoń
cichon@eko.uj.edu.pl |
Dep. of Population Ecology Inst. of Environmental Sciences Jagiellonian University Gronostajowa 7, 30-387 Kraków Poland tel. + 48 12 664 52 01 fax + 48 12 664 69 12 |
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Cichoń M., Linden M.
IBIS
1995; 137: 364-370
Abstract:
The relationship between the timing of breeding, offspring weight and offspring recruitment was investigated in two populations of Great Tits Parus major. In two of six seasons a significant negative correlation was found between laying date and fledgling weight, in three seasons the opposite was true, and in one season no significant correlation existed between these variables. Offspring recruitment was quantified in five seasons and late nesting birds were found to produce significantly fewer recruiting offspring in two of these, the same two seasons when late fledglings had significantly lower weights. No significant correlation existed between the number of recruits and laying date in the three seasons when late fledglings were as heavy or heavier than early fledglings. The potential detriment to reproductive success by lateness was thus offset when late nesting parents managed to produce heavy young. Between year variations in the seasonal pattern of reproductive success has previously been suggested to contribute to the maintenance of variability in the timing of breeding in Great Tits. In this paper it is suggested that producing heavy offspring late in the season might be a proximate factor influencing the seasonal patterns of reproductive success. Producing heavy offspring late in the season is probably not a "strategy", but rather an effect of chance differences between years in the seasonal availability of food, or the seasonality of other factors important for the nesting birds.
d e s i g n e d b y P a w e ł K a p u s t a