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It is well documented that extra-pair copulations are a strategy by which males can increase their reproductive success and females may obtain genetic benefits. Whereas in monogamous species extra-pair copulations are the only way for both sexes to increase their reproductive success, in polygamous systems both partners can benefit from mating with several individuals. Here we examine the intensity of sperm competition and the rate of extra-pair fertilizations in relation to male anti-cuckoldry tactics in a small passerine, the polygynandrous penduline tit (Remiz pendulinus), where both sexes have the opportunity to become polygamous.

The results revealed rather low rates of extra-pair paternity for this species: 6.9% (14 out of 201) of young being sired by an extra-pair male. Males build elaborate nests to attract females and because of this high initial investment, one would expect males to evolve anti-cuckoldry tactics to ensure paternity. However, male mate guarding intensity as well as within-pair copulation frequency were rather low in comparison to other polygynandrous species, and hence both strategies are unlikely to ensure paternity. In fact our results show that those males which deserted their females early in their fertile cycle (already before the second egg is laid) did not lose paternity, whereas those males which tended to guard their females throughout their whole fertile period were more likely to be cuckolded. Thus, although no obvious anti-cuckoldry tactics exist in this species, extra-pair paternity is very low. This indicates a tendency in females to cooperate with their pair-males rather than seek extra-pair copulations.