Experimental mate replacement does not increase extra-pair paternity in tree swallows

Before the onset of female fertility, we removed 12 early–settling male tree swallows (Tachycineta bicolor) from their nest–boxes and mates, and allowed replacement males which had been floaters to settle with the original female residents. We predicted that females which had their original mate choice altered (experimentals) would be more likely to obtain extra–pair fertilizations than females which remained paired with their original, early–settling mates (controls). The proportion of females obtaining extra–pair fertilizations, however, did not differ between controls and experimentals, indicating that mating tactics of female tree swallows were unaffected by mate replacement. However, differences between early–settling and replacement males did exist. Replacement males had shorter wing chords than early–settling males, suggesting that they were younger. Moreover, a significantly greater proportion of replacement males than early–settling males were unringed and thus new to the study site. Our results suggest that if females are choosing males for good genes, then early–settling males are not superior in genetic quality to the smaller replacement males which had originally been floaters.