Lesser Woodcreepers (Xiphorhynchus fuscus) excavate nest cavities in trees

To understand the evolution, life-history trade-offs, and population ecology of cavity nesters, it is critical to identify the avian lineages and circumstances in which birds excavate tree cavities. Woodcreepers (Furnariidae: Dendrocolaptinae; 56 species) are considered non-excavators dependent on existing cavities. We overturn this assumption by providing definitive evidence that the Lesser Woodcreeper (Xiphorhynchus fuscus, 23 g) is a facultative tree-cavity excavator. From 2007 to 2022 in the Atlantic forest of Misiones, Argentina, they nested in pre-existing tree crevices (4 nests), or excavated in trunks of large-diameter trees or stumps in advanced stages of decay (mean: 58 cm diameter; range: 22–121 cm; 22 nests). Nest entrances were vertically elongated and chambers were usually pocket-like, excavated in the exterior of the trees (sapwood), with floors that curved along the trees' circumference. Excavating woodcreepers pulled out elongated, fibrous pieces of decayed wood with a ...