Offspring sex ratio and male quality in Goshawk Accipiter gentilis
Keywords:sexual dimorphism, mating systems, breeding biology
In some bird species, brood sex ratios have been shown to vary with male quality and time of season. Sex ratio adjustment in favour of males would be adaptive if sons inherit their fathers characters that increased their attractiveness to females. In species without obvious sexual ornaments, as in Goshawks, female choice must be based on other characters. One possible male quality character is his ability to defend and protect a good territory. Brood sex ratios skewed towards males have been reported in Goshawks, but only in broods of four young did the male/ female ratio differ significantly. In the present study of Goshawks in Sweden I registered a total number of 953 females and 1,054 males (=52.5% males) in 745 broods, which is significantly different from parity. However, in the 116 broods with four young I did not find any evidence for my hypothesis about different sex ratio among clutches or territories.
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