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

Extrapair paternity (EPP) has proved to be widespread and highlyvariable among birds and other taxa, including socially monogamousspecies. A multitude of hypotheses have been put forward toexplain this variation, but its occurrence is not fully understood.Male age, social dominance rank, song and breeding density orsynchrony have been among the suggested correlates of EPP, butresults so far are inconclusive. We interspecifically cross-fosteredblue tits (Parus caeruleus) and great tits (Parus major) inthe wild, thus manipulating males to exhibit reduced socialdominance rank, sing aberrant songs, and consequently be perceivedas low-quality males as compared to controls. This allowed usto test if male quality had an influence on loss of paternity.We found no statistically significant differences between cross-fosteredand control males of either species, neither with respect tolevels of cuckoldry nor proportions of extrapair young (EPY)in the broods. Paternity levels were comparable to other studieson the same species. No effect of density could be detectedon levels of EPP either, while an age effect seemed to be presentat least in the blue tit, EPY being almost absent in broodsof older blue tit males. We conclude that the effects of malequality on paternity loss are minor, if any, in these populations.