Intraspecific fledgling adoption by a pair of superb fairy-wrens, Malurus cyaneus.

Adoption is a form of alloparenting in which an individual raises an unrelated offspring, although it is sometimes unclear whether this behaviour is adaptive or the product of reproductive error. Here, we report an observation of intraspecific adoption in a cooperatively breeding songbird, the Superb Fairy-wren Malurus cyaneus. In a colour-banded population at Cleland Conservation Park, South Australia, a breeding pair with three nutritionally dependent fledglings adopted an additional male fledgling from an adjacent territory. The adoptee was first observed with the new group about 2 weeks after fledging and was regularly fed by his adoptive parents. The fledgling continued to associate with his adoptive group for at least 7 months,even though his natal group remained intact in the adjacent territory. Genetic analyses confirmed that the adopted fledgling was the product of within-pair mating and was not closely related to its adoptive parents. There is some evidence that adult fairy-wrens may discriminate against offspring based on the acoustic structure of their begging calls; however, begging calls recorded at the adoptee’s nest were equally similar to incubation calls from both the genetic and adoptive mother. Finally, we discuss similar instances in the literature of intraspecific and interspecific adoption by Superb Fairy-wrens and suggest possible explanations for this behaviour.