Cavity nesting by a pendant nest–building species, the Bushtit (Psaltriparus minimus)

Abstract

Plasticity in bird nest placement is relatively understudied compared to many other aspects of breeding biology. We describe an unusual nest of a Bushtit (Psaltriparus minimus) that was placed inside an old woodpecker cavity instead of being attached to the foliage of a tree or shrub. A pair of Bushtits successfully fledged one brood inside this cavity and then immediately constructed a second nest in the same cavity. Concurrent with this second nesting effort, a Tree Swallow (Tachycineta bicolor) actively competed with the Bushtits for the same cavity and was seen nest building in the cavity as well. The apparent rarity of cavity nesting by the Bushtit suggests this nesting effort was serendipitous and perhaps facilitated by the dimensions of the cavity, which were similar to the hanging, pendulous nest this species typically builds.