EXTRAPAIR PATERNITY IN THE BLUE TIT (PARUS-CAERULEUS) - FEMALE CHOICE, MALE CHARACTERISTICS, AND OFFSPRING QUALITY

Extrapair paternity is common in many birds, and it is now generally a ccepted that female choice plays an important role. However, the benef its that females obtain from extrapair paternity are much less clear. To test the hypothesis that females obtain indirect fitness benefits, we studied paternity in a blue tit population over 4 years. Extrapair paternity occurred in 31-47% of all nests and accounted for 11-14% of all offspring. Most males that fathered extrapair young did not lose p aternity themselves, males never ''exchanged'' paternity, and within n ests the extrapair offspring were usually fathered by a single male. C omparisons between males that did and did not lose paternity and pairw ise comparisons between the extrapair male(s) and the within-pair male showed that successful males had longer tarsi and sang on average lon ger strophes during the dawn chorus. Successful males weighed less (re lative to their size) during the nestling stage, but nevertheless they survived better: Male age did not influence their likelihood of losin g paternity, but extrapair males were usually older than the within-pa ir male they cuckolded. Within nests with mixed paternity extrapair yo ung were more likely to survive than within-pair young in cases of par tial brood mortality. Our data also suggest that extrapair offspring w ere more likely to be males. Because extrapair males were usually clos e neighbors, male quality should be considered relative to the quality of the neighbors. Despite this, we found consistency in female choice over years. Our observations provide support for the hypothesis that female blue tits engage in extrapair copulations to obtain good genes for their offspring.