Generally brownish birds, the true woodcreepers maintain an upright vertical posture, supported by their stiff tail vanes, and feed mainly on insects taken from tree trunks. They range from 14 to 35 centimetres in length. However, woodcreepers often form part of the core group at the center of flocks attending army ant swarms. Though unrelated, they superficially resemble the Old World treecreepers. Woodcreepers are arboreal cavity-nesting birds; 2-3 white eggs are laid and incubated for about 15 to 21 days.
These birds can be difficult to identify in that they tend to have similar brown upperparts, and the more distinctive underparts are hard to see on a bird pressed against a trunk in deep forest shade. The bill shape, extend/shape of spots/streaks, and call are useful aids to determining species.
Interestingly, the xenops, which were usually considered to be ovenbirds with a somewhat woodcreeper-like plumage, are in fact closely related to the latter (Fjeldså et al., 2005). They are best considered to form a separate tribe and give a good impression of how the ancestors of the woodcreepers must have looked like. The true woodcreepers are characterized by a belly feather growth pattern not found in any other birds.
The systematics of the Dendrocolaptinae were reviewed by Raikow (1994, based on morphology) and Irestedt et al. (2004, based on analysis of nuclear and mitochondrial DNA sequences). As the latter paper revealed, the commonplace convergent evolution of bill morphology hampered Raikow's analysis. Color patterns, on the other hand, were more in agreement with the molecular data, but the generally drab coloration of the woodcreepers renders this character less informative than desirable. The work of Irested et al., on the other hand, was severely limited by unavailability of samples of many phylogenetically interesting taxa.
For example, the Deconychura species apparently belong into separate genera, but only D. longicauda was available for molecular analysis. Moving Lepidocolaptes fuscus to Xiphorhynchus restores monophyly of Lepidocolaptes, and Xiphorhynchus was very much under-split (Aleixo, 2002a,b). Hylexetastes may contain anything from 1 to 4 species.
It remains unresolved whether the Scimitar-billed and Long-billed Woodcreepers' distinctiveness is due to strong selective pressure (and therefore rapid morphological evolution) of forms related to Lepidocolaptes and Dendrexetastes, respectively, or to long-time evolution of distinct lineages which separated early in the evolution of the group, with genetic similarity due to long branch attraction. The data gained from the myoglobin intron II DNA sequence disagrees strongly with mtDNA cytochrome b sequence data regarding the validity of Lepidocolaptes in general Irestedt et al. (2004); as the latter agrees much better with morphological and biogeographical data it therefore is used here.
More detailed studies are needed to resolve these questions, namely reevaluation of morphological data in the light of the molecular findings, and new molecular studies which thoroughly sample the questionable genera.
Additionally, the species-level taxonomy of several groups requires further study. Examples of "species" where vocal and morphological variations suggests that more than one species-level taxon could be involved are the Curve-billed Scythebill and the White-chinned, Olivaceous, Strong-billed and Straight-billed Woodcreepers.
Subfamily Dendrocolaptinae - woodcreepers
Tribe Xenopini - xenops
Tribe Dendrocolaptini - true woodcreepers