| 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., Sendecka J., Gustafsson L.
J AVIAN BIOL
2005; in press
Abstract:
An increasing number of studies have demonstrated that brood sex ratios are frequently unequal, but the proximate mechanisms underlying this deviation are largely unknown. In the current study we analysed deviation from expected 1:1 sex ratio among dead embryos from unhatched eggs collected from partially unhatched clutches of three passerine bird species. We showed that male embryos were significantly overrepresented among unhatched eggs of great tits, blue tits and collared flycatchers. Moreover, the bias in sex ratio differed among species and tended to differ among study years. We discuss several hypotheses to explain the observed male bias among unhatched eggs. We conclude that sex specific embryo mortality may contribute to explain the observed variation in sex ratios in several species of wild birds and that sexing unhatched eggs is important in the studies of sex ratio allocation.
d e s i g n e d b y P a w e ł K a p u s t a