In their commentary on Krams et al. (1), Lifjeld and Slagsvold (2) argue that there may be two reasons for observing mixed paternity in broods of pied flycatchers (Ficedula hypoleuca): 1) females mate with males other than their social mate or 2) females switch from being secondary mates of polyterritorial males to pairing with another male within the 2 to 3 d of their fertile period. The first instance will fall within the concept of extra-pair mating, while the latter may be categorized as sequential monogamy. We argue that this strict categorization of dynamic mating behaviors may restrict our understanding, emphasizing male–male competition at the expense of adaptive female behavior. In fact, theory predicts that paternity in a neighboring nest incentivizes males to defend against nest predators (3), as demonstrated in our experiments (1), and that females benefit irrespective of the sequence of pair bonding and copulatory events.
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