Sperm numbers on the perivitelline layers of blue tit eggs are repeatable within a clutch, but independent of the occurrence of extra-pair paternity

Peter Santema, Kim Teltscher & Bart Kempenaers
In many socially monogamous bird species, females produce offspring sired by males other than their social partner. A large body of research has aimed to elucidate the evolutionary causes and consequences of such extra-pair paternity, but relatively little is known about the underlying behaviour. The number of sperm on the egg’s perivitelline layers (PVL) is related to recent copulation activity and may thus give some insight into the female’s mating behaviour. We used a simple...
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