1 Citation 54 Views
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
spongy texture, tapping only when inside cavities. Published and online
photographs of nests of Xiphorhynchus species suggest that excavation may
be widespread in the genus. Our observations that woodcreepers tore out
elongated pieces of spongy wood (rather than hammering) are consistent
with the idea that their long, thin bills are more resistant to torsion
and less resistant to impact compared to the stouter bills of other
excavators in Passeriformes and Piciformes. Research has tended to focus
on birds with chisel-shaped bills, perforating harder sapwood to create
nesting chambers in the center of heartrot-infected trees (resulting in
typical woodpecker cavities, with circular floors). We hypothesize that
Lesser Woodcreepers have adopted an alternative strategy, selecting large
trunks with soft outer wood (sapwood), stopping their excavation radially
if they reach harder wood, and then expanding the nest chamber laterally.
Furnariidae may offer a useful model family for understanding ecological
and evolutionary factors that influence cavity excavation.
54 views reported since publication in 2023.