A Mixed Brood Following Usurpation of a Carolina Chickadee Nest by Tree Swallows

Naturally occurring mixed species broods are uncommon but can occur due to nest parasitism, and in rare cases, due to usurpation. We report on a mixed brood resulting from a pair of Tree Swallows usurping a Carolina Chickadee nest. The chickadee nest was constructed in a nest box, and 1 egg was laid prior to usurpation. This egg, in addition to the clutch of swallow eggs, was incubated, hatched, and fed by the adult swallows. The chickadee nestling grew and appeared to be healthy at 6–7 days of age, but was approximately 50% smaller than its nest mates at that time. The chickadee died after 8 days, most likely due to starvation. The remaining Tree Swallow nestlings were reared to fledging by the adults.