Sexual promiscuity in female songbirds increases the reproductive success of their offspring.Nicole Gerlach at Indiana University in Bloomington and her colleagues studied free-living dark-eyed juncos (Junco hyemalis). The birds form a 'social pair' with one partner but produce more than one-quarter of their offspring from 'extra-pair' mating. These young go on to reproduce more successfully than those sired within the social pair.
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