Manipulation of male quality in wild tits: effects on paternity loss

Extrapair paternity (EPP) has proved to be widespread and highly variable among birds and other taxa, including socially monogamous species. A multitude of hypotheses have been put forward to explain this variation, but its occurrence is not fully understood. Male age, social dominance rank, song and breeding density or synchrony have been among the suggested correlates of EPP, but results so far are inconclusive. We interspecifically cross-fostered blue tits (Parus caeruleus) and great tits (Parus major) in the wild, thus manipulating males to exhibit reduced social dominance rank, sing aberrant songs, and consequently be perceived as low-quality males as compared to controls. This allowed us to test if male quality had an influence on loss of paternity. We found no statistically significant differences between cross-fostered and control males of either species, neither with respect to levels of cuckoldry nor proportions of extrapair young (EPY) in the broods. Paternity levels were comparable to other studies on the same species. No effect of density could be detected on levels of EPP either, while an age effect seemed to be present at least in the blue tit, EPY being almost absent in broods of older blue tit males. We conclude that the effects of male quality on paternity loss are minor, if any, in these populations. Copyright 2005.