Adoption of yellow warbler nestlings by song sparrows.

Although interspecific brood adoption has been reported in several species of birds, the process by which it occurs has seldom been reported. We observed a pair of Song Sparrows (Melospiza melodia) that adopted a brood of Yellow Warblers (Dendroica petechia) and, gradually, over several days, took over the parental duties of the original parents. During the first five days of the nestling period, the brood was only attended by Yellow Warblers. In the following three days, however, a pair of Song Sparrows took over an increasingly larger proportion of the parental duties. This adoption probably resulted from misdirected parental care. Although the factors that led to the adoption are unknown, it is clear that the absence of the original parents was not prerequisite.