A pair of Roseate Terns adopts another pair's egg

Most cases of adoption in Common Terns (Sterna hirundo) occur when a chick leaves (or is moved from) its nest site and adopts new parents (Ian Nisbet, pers. comm.). It is not known to what extent similar behavior occurs in Roseate Terns (S. dougallii), however, because (except for studies of chick-provisioning Richards and Schew 1989, Teets 1998, Shealer 1999) until recently, little behavioral work has been done with chicks of this endangered species (Nisbet 1989, Schew and Richards 1989, Grinnell and Spendelow 2000). Here we report a case where a pair of Roseate Terns abandoned their egg a few days prior to the hatching of the chick. Another pair took over incubation of the egg and then raised the chick to fledging, demonstrating that an adoption can be initiated by adult terns.