Woodcreepers (dendrocolaptidae)

Class AVES Order PASSERIFORMES Suborder TYRANNI Family DENDROCOLAPTIDAE (WOODCREEPERS) free text from the Handbook of the Birds of the World

Straight-billed Woodcreeper

Straight-billed Woodcreeper, near Wanica, Surinam. Picture by Jan Dolphijn

Small to medium-sized birds with broad rounded wings, long tail with rigid shafts, outer and middle toes united and much longer than inner toe, front claws strongly curved; most with brown plumage, a few grey to blackish, all with rufescent wings and tail.
13-36 cm.
Neotropical Region.
Forest and woodland, a few in semi-open habitats.
13 genera, 52 species, 270 taxa.
1 species threatened; none extinct since 1600.
The Dendrocolaptidae, the woodcreepers, are part of an endemic Neotropical group of birds known as the tracheophone suboscines. These primitive passerines possess an elaborate tracheal syrinx, of similar form in each one, and have evolved a diverse array of ecological specializations. Most woodcreepers are specialized tree-climbers, extremely well adapted to an arboreal life. Not surprisingly, their centre of diversity lies in the rich, forested lowlands of the Amazon Basin, where up to 19 species occur together. The Dendrocolaptidae were formerly known as “woodhewers”, a name derived from early accounts that referred to these birds as “picicules”, meaning “little woodpeckers (Picidae)”. This name, however, was abandoned in favour of one that more appropriately reflects their habits, which seldom include pecking or hammering in the manner of true woodpeckers.

As with most passerines, the fossil record of woodcreepers is scant, providing no insight into the age of their lineage. Only a few Quaternary fossils are known, all from two sites in Brazil. One of these is the Lapa da Escrivania, near Lagoa Santa, in Minas Gerais, where one fossil from the Pleistocene, of the White-throated Woodcreeper (Xiphocolaptes albicollis), and two others, one Pleistocene and the other Holocene, of the Narrow-billed Woodcreeper (Lepidocolaptes angustirostris) have been discovered. According to H. Alvarenga, specimens of Xiphocolaptes species have been found at another site in Brazil. The recent assertion, by J. Cheneval, that a middle Miocene fossil, Homalopus picoides, first discovered in the mid-nineteenth century at Sansan, in France, represents a dendrocolaptid must be viewed with caution. There is no evidence to suggest that tracheophone suboscines ever existed outside the New World. Any attempt to establish confidently that they did would require more than the extremely fragmentary material available, which includes only the distal end of a left tarsometatarsus and the proximal end of a right humerus. Although the fossil does show certain similarities to tree-creeping birds, S. L. Olson suggested that Homalopus might have been an oscine that was only convergently similar to suboscines. Molecular data clearly indicate that the woodcreepers diverged relatively recently from the ovenbirds (Furnariidae), with the split probably occurring during the Miocene.

Evidence from both morphology and molecular genetics strongly supports a monophyletic assemblage including both woodcreepers and ovenbirds, a much larger group of birds that has radiated into a highly diverse array of niches and forms. This close relationship has resulted in the taxonomic rank of these two groups being unsettled, with many treatments combining them as one family, either under the name Dendrocolaptidae, as in older classifications or, as in more recent ones, under the name Furnariidae; in either case, the woodcreepers have consequently been ranked as a subfamily, the Dendrocolaptinae. Only these two avian families, the Dendrocolaptidae and the Furnariidae, possess two intrinsic muscles of the syrinx, the vocalis dorsalis being absent in other tracheophone suboscines. In addition, analyses of both DNA-DNA hybridization data and sequences of nuclear and mitochondrial DNA support the view that the woodcreepers and the ovenbirds form a closely related group that is distinct from other birds. Nevertheless, dendrocolaptids differ from furnariids in a number of features. Characters traditionally used to diagnose woodcreepers include horns on the processi vocales of the syrinx, these horns being present in no furnariids other than the miners (Geositta); nostrils that are rounded at the rear, a condition known as holorhinal; and outer and middle toes that are united at the base, of similar length, and noticeably longer than the inner toe. All woodcreepers share these features to a degree, but not all ovenbirds can be excluded by them. Notably, several “intermediate” woodcreeper genera, namely Dendrocincla, Deconychura, Sittasomus and Glyphorynchus, exhibit a mixture of morphological characters, having some features of “typical” dendrocolaptids and others that are more typical of furnariids, and particularly of the foliage-gleaners, the six genera of which (Anabacerthia, Syndactyla, Philydor, Anabazenops, Automolus, Hylocryptus) are sometimes considered to constitute the subfamily Philydorinae. Some authors, therefore, cite the aforementioned four dendrocolaptid genera as demonstrating a clear link between the two families.

A diverse array of evidence indicates that all extant woodcreeper genera are more closely related to each other than they are to any furnariid. All dendrocolaptids share a particular configuration of their feather tracts (pterylosis) that distinguishes them from all other passerines. Further, they are unique among the passerines in having extensive ossification of the tendons of the hind limb, an adaptation to their tail-braced, scansorial habits that is reduced or more variable only in the genus Dendrocincla, the members of which less frequently adopt scansorial postures. Platyacarus feather mites are known to parasitize only woodcreepers, with documented hosts in every genus except the monotypic Drymornis; the latter, containing the Scimitar-billed Woodcreeper (Drymornis bridgesii), retains many morphological characters, especially those of the limb muscles, that are primitive among woodcreepers (see Morphology). DNA-DNA hybridization data, coupled with phylogenetic analyses of various morphological and molecular characters, consistently yield results suggesting that all dendrocolaptid genera are monophyletic to the exclusion of furnariids. In contrast, the Furnariidae appear not to be monophyletic with respect to woodcreepers.

The issue of whether to rank woodcreepers as a separate family has been questioned recently by M. Irestedt and colleagues, whose estimated phylogeny based on both nuclear and mitochondrial DNA suggested that the furnariid leaftossers (Sclerurus) are basal both to woodcreepers and to all other ovenbirds. Because of this arrangement, those authors recommended that the Furnariidae include three subfamilies: woodcreepers (Dendrocolaptinae), leaftossers (Sclerurinae), and all other ovenbirds (Furnariinae). An alternative classification, not mentioned by Irestedt and co-workers, would be to accord family rank to each of these groups. The placing of the woodcreepers in a family of their own seems the best course, because woodcreepers form a clearly diagnosable yet diverse group of species that share distinctive morphological and biochemical traits. Moreover, incorporation of them within the ovenbird family would also create too inclusive a group, comprising nearly 300 species, that obscures important evolutionary differences among its members.

Some scientists have speculated that it was in the vast Amazon Basin that the woodcreepers evolved from their supposed nearest living relatives, the foliage-gleaners. In his monograph on the relationships of furnariids and dendrocolaptids, A. Feduccia postulated that, on the basis of similarities in anatomy, behaviour and geographical distribution, ancestral woodcreepers were foliage-gleaners that were capable of tree-climbing, an adaptation that may have greatly reduced competition for feeding space in mixed-species foraging flocks. According to this hypothesis, tree-climbing foliage-gleaners then experienced an extensive radiation in this new foraging space, leading eventually to modern woodcreepers.

Cinnamon-throated Woodcreeper, near Lelydorp, Surinam. Picture by Jan Dolphijn

Shortly after Feduccia’s monograph, E. O. Willis, whose extensive observations of woodcreeper behaviour and ecology are perhaps unparalleled, suggested an alternative view of dendrocolaptid evolution. He noted that woodcreepers of the genus Dendrocincla and leaftossers of the ovenbird genus Sclerurus were strikingly similar in appearance and behaviour. On this basis, he proposed that tree-climbing woodcreepers might have evolved from terrestrial leaftosser ancestors lured upwards to exploit food on bare tree trunks in forests, and perhaps driven there through competition with the evolving thamnophilid antbirds that now dominate ant-following flocks in the understorey. Under this scenario, the genus Dendrocincla represents a primitive woodcreeper that has advanced little. This apparent link with leaftossers was not supported by anatomical analyses of woodcreeper-ovenbird relationships, but evidence of it has emerged recently in analyses of mitochondrial and nuclear DNA sequences. Using these biochemical characters, Irestedt and colleagues have proposed a phylogeny for the tracheophone suboscines. Their study included, among several other taxa, a single leaftosser, the Rufous-breasted Leaftosser (Sclerurus scansor), as well as five species of dendrocolaptid, among them the Plain-brown Woodcreeper (Dendrocincla fuliginosa). Those authors found that the leaftosser emerged as ancestral to all woodcreepers as well as to all other ovenbirds. In spite of sampling limitations, this supports the view that both families may have evolved from a woodcreeper-ovenbird ancestor that bore some similarities to extant species of leaftosser.

On the basis of anatomical and molecular characters, there are two major lineages of woodcreepers. One of these comprises species in the four genera that are “intermediate” between the Dendrocolaptidae and the Furnariidae: Dendrocincla, Deconychura, Sittasomus and Glyphorynchus. The other lineage, known as the “strong-billed” group, comprises all other dendrocolaptid species. The several characters possessed by the “intermediate” taxa that are thought to be ancestral and are shared with the ovenbirds include less stiffened shafts of the tail feathers and reduced ossification of the leg tendons in Dendrocincla, the presence of wingstripes in Sittasomus and Glyphorynchus, and particular features of the skull. The “strong-billed” woodcreeper genera exhibit several derived characters, many associated with their ubiquitous creeping behaviour and trunk-foraging lifestyle, such as the “closed” two-notched sternum, a heavily ossified skull, extensive ossification of the leg tendons, and a well-developed pygostyle.

Whether the “intermediate” lineage is the more basal within the Dendrocolaptidae remains controversial. R. Raikow’s estimate of woodcreeper phylogeny, based on characters derived from hind-limb and bill morphology, found that two monotypic genera, Nasica and Drymornis, emerged as basal to all woodcreepers; Drymornis was the more primitive of the two, as determined by its retention of ancestral character states, as opposed to its specialized bill shape and ground-foraging behaviour. By contrast, two recent phylogenetic studies employing both nuclear and mitochondrial DNA sequences supported the placement of Nasica and Drymornis in the “strong-billed” assemblage. Neither study included both genera in the same analysis with other woodcreepers, one having sampled Drymornis and the other only Nasica. A possible explanation for the conclusions of the morphological study is that the wide variability in substrates used by tree-climbing birds has led to a great plasticity in anatomical characters associated with feeding and climbing, rendering characters associated with these traits less useful for phylogenetic analysis.

As noted above, woodcreepers in the genus Dendrocincla may be the most primitive within the family, a hypothesis reflected in most linear classifications. All six species in this apparently monophyletic genus have rectrices with a somewhat less rigid shaft and a reduced spiny tip when compared with other dendrocolaptid genera, which exhibit typically rigid shafts with prominent bare, spiny tips that are often curved ventrally. Members of this genus do not depend so much on trunk-foraging, instead catching most of their food by sallying like a tyrant-flycatcher (Tyrannidae); they use vertical trunks mostly for perching, and perch on horizontal branches more often than do most woodcreepers. Within the genus Dendrocincla, species-level taxonomy is in need of study. Widespread species of Dendrocincla, such as the Plain-brown and the White-chinned Woodcreepers (Dendrocincla merula), have several well-differentiated subspecies, some of which may merit recognition as full species when more comprehensive reviews of geographical variation in genetic and vocal characters become available. Within the White-chinned Woodcreeper, differences in vocal characters, size and iris colour suggest that at least two species may be involved. In view of the vocal and plumage differences documented by Willis, it seems better to treat the Plain-winged Woodcreeper (Dendrocincla turdina) of south-eastern Brazil as being distinct from the Plain-brown Woodcreeper, with which it was formerly considered by most authors to be conspecific. Leaving aside turdina, the Plain-brown Woodcreeper has at least three other distinctive groups of subspecies, any or all of which may ultimately be found to be deserving of separate species status.

Willis also noted that the plumage and behaviour of the two Deconychura species suggest that the genus is intermediate between Dendrocincla and Glyphorynchus, with the Spot-throated Woodcreeper (Deconychura stictolaema) being closer to the latter genus. In partial agreement with this suggestion, Raikow’s phylogenetic hypothesis suggested that the two species of Deconychura are not each other’s closest relatives, his findings placing them, along with the Olivaceous Woodcreeper (Sittasomus griseicapillus), in clades intermediate between Dendrocincla and Glyphorynchus. Like the Olivaceous Woodcreeper and the Wedge-billed Woodcreeper (Glyphorynchus spirurus), the two Deconychura species were placed each in a separate clade not closely related to any extant dendrocolaptid. Relationships among the ten taxa currently divided between the two species of Deconychura remain uncertain. For example, within the Long-tailed Woodcreeper (Deconychura longicauda), birds from Central America south to north-central Colombia, forming the “typica group” of subspecies, may be more closely related to the Spot-throated Woodcreeper. Furthermore, there is marked vocal variation within the remaining four, rather morphologically uniform, taxa of the Long-tailed Woodcreeper occurring in Amazonia.

Among the remaining “intermediate” genera, the taxonomy of the Olivaceous Woodcreeper is perhaps the one most in need of a comprehensive, systematic revision of all included taxa. The species can be divided into five major groups according to size and gross plumage coloration. This variation, combined with concordant vocal differences among some groups, is sufficiently marked to suggest that full biological species are involved, this being especially so in the case of three of the groups: each of the two groups occupying eastern Brazil, namely reiseri in the north-east and the “sylviellus group” in eastern and south-eastern Brazil, and the disjunct form aequatorialis on the Pacific coast. Of the remaining subspecies of the Olivaceous Woodcreeper, some that appear similar to each other have distinct vocalizations, but it is uncertain how this variation should be interpreted. Lastly, the small yet distinctive Wedge-billed Woodcreeper is known to possess at least two different song types, although gene flow exists between some morphologically distinct subspecies.

In contrast to the uncertain relationships among the “intermediate” woodcreepers, monophyly of the “strong-billed” clade, exclusive of Nasica and Drymornis (see above), has been corroborated by a number of investigations. A study of mitochondrial DNA (mtDNA) sequences supported the division of the “strong-billed” woodcreepers into two clades, one containing the genera Dendrexetastes, Hylexetastes, Xiphocolaptes and Dendrocolaptes, and the other consisting of Campylorhamphus, Lepidocolaptes and Xiphorhynchus.

Molecular and anatomical characters are strongly indicative of a sister relationship between the genera Hylexetastes and Xiphocolaptes. The first of those contains only two species, both confined to the Amazon Basin, while the four species of Xiphocolaptes are distributed in a variety of forested habitats from Mexico south to central Argentina. Species-level taxonomy within these genera merits further study. In the genus Hylexetastes, two species, the Red-billed Woodcreeper (Hylexetastes perrotii) and the Bar-bellied Woodcreeper (Hylexetastes stresemanni), have traditionally been recognized, although some authors have elevated the subspecies uniformis of the former to a full species, the “Uniform Woodcreeper”. In 1995, the taxon brigidai was, on the basis of plumage, described as a new species, “Brigida’s Woodcreeper”, but its appearance is close enough to that of uniformis that hybrids would be difficult to detect. Vocal similarity among these and other Hylexetastes taxa, coupled with limited morphometric differences, supports treatment of all as subspecies of the Red-billed Woodcreeper. Plumage patterns in Hylexetastes are comparable to those in the sympatric populations of the Amazonian Barred Woodcreeper (Dendrocolaptes certhia), which appear to constitute a single species.

The four Xiphocolaptes have a significantly longer bill than that of the two Hylexetastes, to which they are otherwise nearly identical morphologically. This morphological similarity is reflected in their placement as sister taxa in a recent phylogeny. Unlike species in the genus Hylexetastes, those in the genus Xiphocolaptes differ notably in plumage and structure. Morphology within the genus is constant, all members being large and heavy-bodied, with the tail relatively short, and the bill long, massive and laterally compressed. Xiphocolaptes formed a monophyletic clade in a phylogenetic analysis that sampled three of the four species. Three species are largely restricted to discrete biogeographical regions, within which geographical variation is subtle. The White-throated Woodcreeper has three subspecies in the Atlantic and Planalto forests of eastern and south-eastern Brazil and adjacent portions of Argentina and Paraguay. The Great Rufous Woodcreeper (Xiphocolaptes major), a Chaco species, has four subspecies in Bolivia, south-west Brazil, Paraguay and northern Argentina. The rare Moustached Woodcreeper (Xiphocolaptes falcirostris) is distributed spottily in deciduous forests of the Caatinga region of north-eastern Brazil. Unlike its three congeners, the Strong-billed Woodcreeper (Xiphocolaptes promeropirhynchus) occurs over a vast range and exhibits tremendous geographical variation in plumage and habitat preference. There are currently 25 recognized subspecies, divided into three groups: the “emigrans group” in Central America, the “promeropirhynchus group” living in the Andes of northern South America, and the “orenocensis group” of the Amazonian lowlands and the foothills of the tepuis. C. Cory and C. Hellmayr hypothesized that the “orenocensis group” is a separate species, the “Great-billed Woodcreeper”, and others have raised the possibility that all three groups may represent distinct species. Some taxa in this genus have had a tortuous taxonomic history. Recent analysis of plumage characters revealed that the taxon franciscanus, formerly regarded either as a separate species, “Snethlage’s Woodcreeper”, or as a subspecies of the White-throated Woodcreeper, is instead best treated as the southernmost population of the globally threatened Moustached Woodcreeper. Conversely, a poorly known race of the White-throated Woodcreeper, villanovae from north-eastern Brazil, was formerly considered a subspecies of the Moustached Woodcreeper.

The genus Dendrocolaptes likewise forms a discrete morphological group, but its affinities to other woodcreepers remain uncertain. Some analyses suggest a close relationship between Dendrocolaptes and Hylexetastes, but more recent analyses of anatomical characters favour a sister relationship with Xiphocolaptes and Hylexetastes combined. Analyses of molecular data suggest that Dendrocolaptes occupies a basal position relative to the genera Dendrexetastes and Nasica. Species limits within and between currently recognized species in this genus also remain unsettled. The two barred woodcreepers, with joint populations extending from southern Mexico southwards to the southernmost reaches of Amazonia, were formerly united in a single species, Dendrocolaptes certhia, but differences in morphology and voice between populations occurring north and west of the Andes and those in Amazonia are sufficiently marked that two species are now recognized: the Northern Barred Woodcreeper (Dendrocolaptes sanctithomae) and the Amazonian Barred Woodcreeper, respectively. By contrast, variation in morphology and voice suggests that the form concolor, previously regarded as a separate species under the name “Concolor Woodcreeper”, is best treated as a subspecies of the Amazonian Barred Woodcreeper. Species limits within what apparently constitutes a superspecies of streaked birds, the Black-banded (Dendrocolaptes picumnus), Planalto (Dendrocolaptes platyrostris) and Hoffmann’s Woodcreepers (Dendrocolaptes hoffmannsi), are uncertain. Morphologically, the little-known Hoffmann’s Woodcreeper is unique within the genus, having a long, slim bill and unusual plumage patterns. Although Raikow grouped Hoffmann’s with the two barred woodcreepers, its voice, foraging behaviour and biogeography support Willis’s assertion that it is more closely related to the Black-banded and Planalto Woodcreepers.

Taxonomic confusion in the Dendrocolaptidae is perhaps best exemplified by the largest genus in the family, Xiphorhynchus. This has a broad distribution, and its 15 members exhibit a diverse range of body sizes and ecological adaptations. A. Aleixo’s recent phylogenetic hypothesis, based on variation in mtDNA, helped to clarify many relationships in this vexing genus while at the same time highlighting further challenges. Despite the morphological diversity in the genus, molecular evidence implies that, with the exception of the Straight-billed Woodcreeper (Xiphorhynchus picus) and Zimmer’s Woodcreeper (Xiphorhynchus kienerii), all species of Xiphorhynchus share a common ancestor. These results further combine with patterns of gross morphology and aspects of ecology to support the treatment of most species in one of four groups, but the affinities of two additional species remain unclear. The first group comprises an Amazonian radiation of small dendrocolaptids that characteristically follow mixed-species flocks through the understorey. The second group consists of four ecological generalists occurring from Mexico south to southern Amazonia and eastwards to the Atlantic Forest of Brazil; these species are larger than those in the first group, are less tied to the forest understorey, and forage alone or by following either mixed flocks or army ants. The third group contains two largely montane species, the Spotted Woodcreeper (Xiphorhynchus erythropygius) and the Olive-backed Woodcreeper (Xiphorhynchus triangularis), each of medium size and atypical plumage, that may be foraging specialists on mossy trunks.

The Straight-billed and Zimmer’s Woodcreepers, representing the fourth group, are sibling species that are sufficiently distinct from other Xiphorhynchus to have been treated for many years in the genus Dendroplex. The recent genetic analysis suggested that these two are more closely related to the genera Campylorhamphus and Lepidocolaptes. Notwithstanding this, the return of the Straight-billed and Zimmer’s Woodcreepers to their own genus is not straightforward, because an unfortunate nomenclatural problem complicates the use of the name Dendroplex. Moreover, the bill of Zimmer’s Woodcreeper does not fit the diagnosis for Dendroplex, and this species was consequently placed in Xiphorhynchus even by authors who still classified the Straight-billed Woodcreeper in Dendroplex. Further complicating matters, a recent examination revealed that the holotype of Dendrornis [= Xiphorhynchus] kienerii, described in 1856 and subsequently considered a subspecies of the Straight-billed Woodcreeper, matches Dendroplex [= Xiphorhynchus] necopinus, described in 1934 and known as Zimmer’s Woodcreeper. Dendroplex necopinus is, therefore, a junior synonym of Dendrornis kienerii, and the current scientific name of Zimmer’s Woodcreeper becomes Xiphorhynchus kienerii. Until these various problems are resolved, it is deemed best to retain the Straight-billed and Zimmer’s Woodcreepers in Xiphorhynchus.

Affinities of two other species in this genus are uncertain. The Lesser Woodcreeper (Xiphorhynchus fuscus), occurring in the Atlantic and Planalto forests of eastern Brazil and adjacent areas in Paraguay and Argentina, was for many years classified in the genus Lepidocolaptes. In 1983, Willis suggested that, because of its behaviour, it belonged in Xiphorhynchus; more recent analyses of anatomical and molecular characters place its closest relatives as members of the Amazonian radiation that combines the X. ocellatus and X. spixii species complexes. The Striped Woodcreeper (Xiphorhynchus obsoletus) is similar morphologically to species in the radiation of small Amazonian woodcreepers, but genetic analyses have not resolved its affinities.

Interpreted relationships within each of the four groups of Xiphorhynchus woodcreepers are in a state of flux. Although mtDNA data gave credence to the monophyly of the Amazonian radiation in the first group, consisting of the X. ocellatus and X. spixii superspecies groups, the basal taxon is the Lesser Woodcreeper of the Atlantic Forest. Within the radiation, mtDNA data supported a return to the treatment of the first of those superspecies as comprising three species: the Chestnut-rumped (Xiphorhynchus pardalotus), Ocellated (Xiphorhynchus ocellatus) and Tschudi’s Woodcreepers (Xiphorhynchus chunchotambo). The molecular data likewise supported the results of an independent analysis of plumage by J. Haffer, which indicated that the X. spixii/elegans species complex should be recognized as two species, the monotypic Spix’s Woodcreeper (Xiphorhynchus spixii) of eastern Amazonia and the polytypic Elegant Woodcreeper (Xiphorhynchus elegans) of southern and western Amazonia. The latter now includes not only the nominate race and ornatus, traditionally recognized within X. elegans, but also races juruanus, insignis and buenavistae, all of which have traditionally been placed within X. spixii.

Even more complicated are the taxonomic issues associated with the second group of widespread generalists, and especially the complex now combining the Buff-throated Woodcreeper (Xiphorhynchus guttatus) and the Cocoa Woodcreeper (Xiphorhynchus susurrans). The taxa contained in this complex have been treated variously as constituting either one widespread species or as many as three or four different species. The currently recognized division is unsatisfactory and requires further study. Within the Cocoa Woodcreeper, for example, geographical patterns of song types are more complex than was previously realized, and differences in size do not appear to correspond to current species limits. Taxa within the “susurrans group”, occurring in Trinidad, Tobago and the adjacent Venezuelan mainland, are significantly larger than those within the “nanus group” (“Lawrence’s Woodcreeper”), which range west from central Venezuela into Central America. Moreover, plumage patterns of the former group are so different that authors who merged taxa in the “nanus group” with the remaining South American populations of the Buff-throated Woodcreeper still recognized the Cocoa Woodcreeper proper as being distinct. Molecular analyses suggest that members of the “nanus group” are closely related to races of the Buff-throated Woodcreeper occurring in eastern Brazil and in the north-eastern part of Amazonia, these being, respectively, the nominate race and the subspecies polystictus and connectens. Because members of the “susurrans group” were not examined in this study, however, relationships between it and the “nanus group” remain uncertain.

Taxonomy is in a state of flux even within the Buff-throated Woodcreeper as presently recognized. Molecular data support the merger of the form eytoni, the “Dusky-billed Woodcreeper”, with the western Amazonian populations of the Buff-throated Woodcreeper, a move complemented by variation in plumage coloration but contradicted by marked differences in both bill coloration and vocalizations. These data also indicate a close relationship between the nominate race of the Buff-throated Woodcreeper, from coastal eastern Brazil, and the disjunct forms polystictus and connectens occurring north of the Amazon in Brazil, the Guianas and the Orinoco region of southern Venezuela, all to the exclusion of geographically intermediate Amazonian populations (both eytoni and the “guttatoides subspecies group”). Vocally, the nominate form is relatively similar to populations previously recognized as the Dusky-billed Woodcreeper, with polystictus and connectens similar but of uncertain affinities. Songs of the western Amazonian forms, by contrast, differ strikingly. It is likely, therefore, that the complex of taxa now recognized as the Buff-throated Woodcreeper includes more than one allospecies, but interpretation of variation in voice, morphology and DNA in this widespread dendrocolaptid is in need of more comprehensive sampling.

The other two species in this group of generalists, the Ivory-billed Woodcreeper (Xiphorhynchus flavigaster) and the Black-striped Woodcreeper (Xiphorhynchus lachrymosus), both occur largely or exclusively in Central America. Molecular data suggest that they are each other’s closest relatives; together, they are the sister taxon to the Buff-throated Woodcreeper complex.

The genus Lepidocolaptes is a well-defined group of relatively small woodcreepers, all of which have a slender and decurved bill. With the Lesser Woodcreeper now placed in Xiphorhynchus, as mentioned above, anatomical and molecular data indicate that Lepidocolaptes is monophyletic. Although many earlier authors considered South American populations of the Montane Woodcreeper (Lepidocolaptes lacrymiger) to be conspecific with the Spot-crowned Woodcreeper (Lepidocolaptes affinis), these two taxa differ in voice and plumage. In eastern Brazil, the Scaled (Lepidocolaptes squamatus) and Scalloped Woodcreepers (Lepidocolaptes falcinellus) are now regarded as separate species. They were formerly combined as northern and southern populations, respectively, of a single species, but they exhibit diagnosable differences in plumage, notwithstanding a degree of intergradation where the taxa meet abruptly in south-eastern Brazil. Two of the most widespread species, the Lineated Woodcreeper (Lepidocolaptes albolineatus) and the Narrow-billed Woodcreeper, display substantial geographical variation in plumage, and each has many described subspecies. On the basis of plumage differences, Hellmayr hypothesized that populations of the Lineated Woodcreeper from southern, central and western Amazonia, the “fuscicapillus group”, represent a distinct species, referred to as the “Dusky-capped Woodcreeper”. The songs of the Lineated Woodcreeper also show marked geographical variation. The remaining two of the eight species in this genus are the White-striped Woodcreeper (Lepidocolaptes leucogaster), a Mexican endemic, and the Streak-headed Woodcreeper (Lepidocolaptes souleyetii), which is widespread in Central America and northern South America. In these two, plumage variation is far more subtle, and the latter, despite its broad distribution, exhibits little variation in vocalizations.

Genetics and anatomical features support monophyly of the final genus of the Dendrocolaptidae, Campylorhamphus. On the basis of mtDNA sequences, the five scythebills are most closely related to the genus Lepidocolaptes. Nevertheless, the Greater Scythebill (Campylorhamphus pucherani) not only is the sole member of its genus that has not yet been included in any systematic study, but is also the most divergent both morphologically and vocally. As seems to be the rule among woodcreepers, both of the widespread species, the Red-billed (Campylorhamphus trochilirostris) and the Curve-billed Scythebills (Campylorhamphus procurvoides), exhibit marked geographical variation in plumage, song and habitat preference; each may comprise multiple allospecies. Moreover, habitat preferences and vocalizations imply that some Amazonian populations of the Curve-billed Scythebill may be better treated instead as subspecies of the morphologically similar Red-billed.

Because woodcreeper plumage is cryptically patterned, and because dendrocolaptid anatomy is constrained by foraging behaviour, morphological diagnosis of many species is difficult. There are few avian groups for which the careful analysis of genetic and vocal data is more likely to improve our understanding of systematics and evolution. Future studies must strive to document variation not among a select sample of named taxa but, instead, among populations separated by either vast distances or key barriers to dispersal. Only by using sampling schemes sufficiently thorough to document genetic and vocal variation within populations, and to enable the determination, with a fair degree of certainty, of geographical barriers that correspond to these differences, can one make taxonomic recommendations confidently. Since voice is an indirect measure of reproductive isolation, the analysis of vocal data requires a caution similar to, if not greater than, that demanded in the interpretation of genetic data. Before making taxonomic recommendations based on any type of variation, it is necessary to outline geographical patterns in the characters, to develop a benchmark of variation within populations for later comparison among populations, and to determine, with a reasonable degree of certainty, that the characters being studied are, indeed, important in the process of reproductive isolation. It is essential to bear in mind that, although both genetic and vocal data may be important for understanding species limits, these data are subject to the same pitfalls as are morphological data, our understanding of which has had a century longer to develop.

Morphological Aspects
Although the Dendrocolaptidae are variable in body size, with a total length ranging from 13 cm to 36 cm, most members of the family share a rather uniform body form and plumage coloration. Bill length and shape account for much of the variation. The bill represents more than a quarter of the body length in the Long-billed Woodcreeper (Nasica longirostris), for example, while its extreme curvature in the case of the scythebills results in the distinctive placement of the eyes of those species. The smallest dendrocolaptid is the widespread Wedge-billed Woodcreeper, which, at 13 cm long and weighing 15 g, is not much larger than a Certhia creeper (Certhiidae). The heaviest is the Strong-billed Woodcreeper, up to 169 g in weight and to 35 cm in length, which is a little bigger than a Colaptes flicker of the Picidae family. The majority of woodcreepers are roughly the size of a small thrasher (Mimidae).

Males tend to be larger than females, but broad overlap in both measurements and body mass is typical of most dendrocolaptid species. Pronounced sexual dimorphism in size is exhibited only by the Long-tailed and Spot-throated Woodcreepers, the males of which are considerably larger and heavier than the females. Differences in plumage among woodcreepers are slight, both between young birds and adults and between the sexes. In a few species, especially some Dendrocolaptes, males are recognizable because they raise their crown feathers frequently, producing a somewhat shaggy crest that creates a noticeably different appearance from that of the sleek-headed females. Sexual dimorphism in plumage is otherwise not apparent.

Juveniles differ subtly from adults, but young birds already resemble adults after their first body moult. Immatures tend to be more barred, have a slightly shorter tail, and have a darker or blacker bill that is significantly shorter than the adult’s; the last feature is evident for a relatively longer time than are other characteristics of immaturity.

Woodcreeper plumage does not undergo seasonal change. The only perceivable changes in the feathering are the result of wear and fading, some birds appearing paler late in the breeding season, when many feathers, most notably the remiges and rectrices, are extensively worn.

The predominant coloration of most dendrocolaptids is brown, with the wings and tail contrastingly rufescent. Even such species as the Olivaceous, Olive-backed, Spotted and Black-striped Woodcreepers, which are mostly grey, olive or blackish, exhibit the plain, reddish-brown wings and tail typical of the family. As an overlay on their more subdued coloration, woodcreepers may possess a variegated pattern of streaks, spots and bars on the back, nape, head and underparts. Exceptions to this include the Olivaceous Woodcreeper and most members of the genus Dendrocincla, which are largely unmarked. Most species have creamy, whitish or light brown streaks and tear-shaped spots, but the Elegant, Olive-backed and Spotted Woodcreepers are unique in sharing triangular spots on the back and chest. Barring is usually restricted to the belly, and even then is obvious only on species of Dendrocolaptes, Hylexetastes and Xiphocolaptes. The degree of barring reaches its extreme in the Northern and Amazonian Barred Woodcreepers, each being extensively barred above and below. Two features present only on the Olivaceous and Wedge-billed Woodcreepers are buff axillaries and a conspicuous, buff bar running obliquely across all but the outer remiges. This bar, because it is formed by pale bars on the inner webs of the remiges, is mostly concealed when the wings are folded; it is seen most easily from below on the spread wing, a vantage seldom attainable with living woodcreepers in the field.

Some adaptations designed to resist feather wear or degradation in moist environments seem apparent in the plumage. On many woodcreepers, the tips of the remiges, especially those of the outermost primaries that are exposed on the folded wing, are much darker, containing more melanin than is present in the rest of those feathers. There is a slight tendency towards darker coloration in birds occupying regions of higher relative humidity, in accordance with “Gloger’s rule”, but the pattern is subtle, as has been discussed for some Dendrocolaptes woodcreepers. Species that occupy open habitats may be dramatically countershaded, dark above and light below, in comparison with those that favour the forest interior. The Narrow-billed Woodcreeper, for instance, occurs in open country and has predominantly white underparts. Other examples of dendrocolaptids with relatively pale plumage are the Scimitar-billed Woodcreeper, the Moustached Woodcreeper, and some subspecies of the Red-billed Scythebill that inhabit predominantly open or semi-open landscapes.

Limited data, for a few species, suggest that woodcreepers undergo a single, annual moult that lasts from four to six months. The wings and the tail are typically moulted simultaneously, although wing moult may start first. As with most bird species, the remiges are replaced in sequence from the innermost primary outwards and from the outermost secondary inwards; the rectrices are moulted outwards from the innermost pair. Moult usually follows immediately after the breeding season, but for at least a small number of dendrocolaptids, such as the Northern Barred and Streak-headed Woodcreepers, moult and breeding may overlap. The Amazonian Barred Woodcreeper’s cycle of breeding and moult is believed to extend over a period of nine to ten months, while a female Streak-headed Woodcreeper possessing a brood patch was in the early stages of moult. It is thus possible that some species begin the moult process before their young leave the nest. Overlap of moult and breeding may be an adaptation either for a long moult cycle to be completed before mating and singing resume in the next breeding season or, alternatively, to allow the completion of both during a flush of prey abundance.

The most distinctive aspects of woodcreeper morphology are manifest in their adaptations for tree-climbing, or “hitching”. To some extent, these adaptations are shared with other tree-climbing birds, such as the woodpeckers, a few genera of ovenbirds (e.g. Margarornis and Pygarrhichas) and creepers (Certhiidae), but with important differences and modifications. All woodcreepers are able to hitch up vertical trunks by flexing their legs and hopping forwards; the long and spiky tail holds them in place when they stop. Rigid shafts of the tail feathers facilitate these tail-braced movements and postures. Among all tree-climbing birds, strengthening of the tail shafts appears to be best developed in woodcreepers, which tend to have proportionately longer rectrices. Unlike other birds that use the tail as a brace, however, the woodcreepers’ denuded, spiny rectrix tips are curved downwards like claws, allowing them to contact the substrate at a right angle. The stiffened rectrices with rigid, spiny tips enable the tail to support most of the bird’s weight. Woodcreepers that have lost the tail have great difficulty in climbing.

Several characteristics of the foot and leg are adapted for climbing trees. Woodcreepers have an anisodactyl foot, with three toes pointing forwards and one toe backwards, an arrangement typical of all passerines. Their feet differ from those of most passerines, however, in having the outer and middle toes united for much of their length, and of similar lengths, both being much longer than the inner toe. The hallux is reduced. The claws of the three front toes are strongly curved, aiding in clinging, whereas the claw of the hallux is long and often pressed hard against the substrate, providing support. Strong thighs dominated by strengthened flexor muscles, which have developed at the expense of extensor muscles, provide the power for climbing up trunks. Extensive ossification of the leg tendons appears to be an adaptation for resisting stress on the toes and ankle flexors while clinging to trees. Ossification of the tendons in the legs is reduced, or is more individually variable, only in those woodcreepers that do not rely exclusively on tree-climbing for foraging; these include the Tawny-winged Woodcreeper (Dendrocincla anabatina) and, probably, other species in the genus Dendrocincla. Elaborate tree-climbing adaptations allow dendrocolaptids to exploit several ecological niches, but they also greatly restrict a woodcreeper’s ability to use other modes of locomotion or the wide variety of perches available to most passerines.

Most woodcreepers are exclusively arboreal, moving between trees with a strong, slightly undulating flight. As may be expected for birds that often fly only short distances and glide frequently, the Dendrocolaptidae have broad wings with rounded tips. Many species, especially those that forage in association with army-ant swarms (see Food and Feeding), often approach or briefly land on the ground. Members of the genus Xiphocolaptes seem to spend more time on the ground than do the majority of woodcreepers, the Great Rufous Woodcreeper being the most terrestrial. Only the Scimitar-billed Woodcreeper, with its relatively short tail and unusual hind-limb musculature, seems suited to a terrestrial lifestyle. This species runs on the ground with little difficulty.

The bill is by far the most adaptively variable feature of dendrocolaptid morphology. Its size and shape are closely correlated with foraging behaviour and have evolved along four major themes: gleaning, flycatching, probing, and chiselling. The Wedge-billed Woodcreeper is the only member of the family that has the bill of a typical gleaner. The Olivaceous and Spot-throated Woodcreepers glean with a short, pointed bill, but, as they also sally after prey flushed from trunks, the bill is somewhat broadened at the base. The Long-tailed Woodcreeper and species in the genera Dendrocincla and Dendrocolaptes have a relatively short and straight flycatcher-like bill, characterized by a weak hook at the tip of the maxilla. That of Dendrocolaptes, in particular, recalls the bill of tyrant-flycatchers (Tyrannidae), being relatively short, broad-based, flattened dorsoventrally, and hooked at the tip. These species frequently sally out for prey on the ground, trunks or foliage, or in the air, catching large arthropods and even small vertebrates (see Food and Feeding). Bills used for probing are the most variable in length and shape, being narrower and more delicate compared with other types; in addition, they tend to be compressed laterally, instead of dorsoventrally. In the case of some species, the bill is extraordinarily long and either straight, as that of the Long-billed Woodcreeper, or extremely decurved, as with the scythebills. Dendrocolaptids possessing a probing bill explore a variety of cavities in tree and fern trunks, dead-leaf clusters, bamboo stems and epiphytes. Willis noted that species with a straight bill tend to probe from a lateral position, whereas those with a decurved bill probe from a vertical position. Many species with a probing bill also glean insects from bark or occasionally sally out after flushed prey.

Straight-billed Woodcreeper, near Wanica, Suriname. Picture by Jan Dolphijn

Bills used for chiselling, seen on members of the genera Hylexetastes and Xiphocolaptes, are a variation of those used for probing. Such bills are laterally compressed and relatively deep and heavy. Species having this type of bill capture large prey on trunks, or tear apart decaying material accumulated on branch forks and in epiphytes. The bill of Hylexetastes is similar to that of Xiphocolaptes, but is shorter. The two Hylexetastes woodcreepers are more generalist foragers, at times sallying out for prey in the manner of many woodcreepers that have a flycatcher-like bill.

Woodcreepers inhabit chiefly forest or woodland, from tropical rainforest in the lowlands to stunted cloudforest near the timber-line, but a few species occur in savanna or other semi-open habitats. Most are restricted to tropical evergreen forest, although some are plentiful in semi-deciduous woodland and gallery forest in drier regions. A small number occur in pine-oak (Pinus-Quercus) woodland and pine forest in the mountains of Central America, and others frequent montane evergreen forest or cloudforest in the Andes and other mountain ranges. The Polylepis woodlands of the high Andes and the temperate forests of southern South America are perhaps the only forested habitats in the Neotropics that are devoid of woodcreepers. As a result of their sedentary nature and their aversion to crossing large unforested gaps, few dendrocolaptid species inhabit offshore islands.

Most woodcreepers are found in lowland forest, but a few occupy higher elevations. The vast majority of this family’s members are restricted to tropical lowlands from sea-level to elevations mostly below 1000 m, with some species occurring sparingly to 1500 m. Above this altitude, the Tyrannine (Dendrocincla tyrannina), Olive-backed and Montane Woodcreepers and the Greater Scythebill are among the few that are largely confined to Andean cloudforest, mostly at elevations ranging from 1500 m up to 3000 m but, depending on the species, locally down to 700 m or, in elfin forest, up to 3400 m. In the mountains of Central America, the White-striped and Spot-crowned Woodcreepers likewise frequent cloudforest, pine-oak woodland and pine-fir (Pinus-Abies) forest, ascending locally to 3600 m. Most lowland and montane dendrocolaptids are found exclusively within their preferred elevations, but a few widely distributed species occur from lowland rainforest up to montane cloudforest. The Strong-billed and Black-banded Woodcreepers are the best examples of this pattern, with some populations of each having strictly montane distributions and others being restricted to the Amazonian lowlands.

The rainforests of the Amazonian lowlands are without doubt the centre of woodcreeper distribution, with many localities harbouring in excess of 15 species and some holding more than a third of all woodcreeper species. Maximum diversity is reached at sites where upland terra firme forest and seasonally flooded várzea and igapó forests exist in close proximity. Most woodcreepers occur in the upland forest, but a few, such as the Long-billed, Striped and Zimmer’s Woodcreepers, are largely restricted to seasonally flooded and river-edge forests. Within each of these habitats, woodcreepers are often segregated by micro-habitat, often through the use of different strata or unique substrates. The scythebills’ specialization on bamboo thickets is a striking example: at some Amazonian sites, both the Red-billed and the Curve-billed Scythebills are to a great extent confined to dense stands of bamboo, mostly Guadua.

Different species of woodcreeper join different types of foraging flocks. Some associate primarily with mixed-species flocks that travel rapidly through the forest, while others join flocks that forage in association with swarming army ants. Species in the genera Xiphorhynchus and Lepidocolaptes often forage with mixed flocks in which most species frequent trunks and branches in the understorey and mid-levels of the forest, but a few, such as the Lineated Woodcreeper, choose instead to seek food in the forest canopy. By contrast, woodcreepers that forage in association with army-ant swarms, examples of which include the White-chinned, Black-banded and Red-billed Woodcreepers, often perch on trunks within a few metres of the ground while awaiting prey, which they capture on or near the ground. Differences among the members of the family in the use of habitat are discussed in greater detail below (see Food and Feeding).

Away from Amazonia, the number of dendrocolaptid species co-existing at a given site drops significantly. In the Atlantic Forest of south-eastern Brazil, for example, no more than eight species are found in sympatry. Likewise, whereas 15-19 woodcreeper species co-exist at many Amazonian sites, only nine have been recorded at the well-worked La Selva Biological Station, in the lowlands of Costa Rica; indeed, only 19 species occur in all of Central America. Regional diversity may be higher where elevational gradients are pronounced because some woodcreeper species show a pattern of altitudinal replacement; at a local level, however, species diversity decreases rapidly at higher elevations.

Most woodcreepers are relatively specialized in their micro-habitat use, with the majority frequenting the understorey and mid-levels of the forest interior. A significant percentage are more flexible in that they regularly frequent forest edge or enter older second growth when it regains the character of mature forest. Far fewer dendrocolaptids inhabit younger second growth, plantations, selectively logged forest or isolated forest fragments, and, in most cases, these are the very species that live in more open habitats.

In addition to the four woodcreepers characteristic of semi-open habitats (see below), there are a few that, despite requiring at least patches of mature forest nearby, seem to be able to exploit a variety of forest types. Near the northern limit of the family’s distribution, the Ivory-billed Woodcreeper occurs in a variety of lowland, montane, deciduous, pine-oak and secondary forests, from sea-level to about 2500 m. Willis even speculated that this species’ behavioural plasticity may give it an advantage over more specialized woodcreepers in the variable climate typical of northern latitudes. It may be a similar plasticity that has allowed the Olivaceous Woodcreeper to become the most widespread member of the family, with a range extending from near the northern edge of woodcreeper distribution, in western Mexico, to near the southern limit, in northern Argentina, and also from sea-level to nearly 2300 m. The Olivaceous Woodcreeper occurs in lowland rainforest in Amazonia and along the Atlantic coast of Brazil, in deciduous woodland on the Yucatán Peninsula and in the caatinga of north-eastern Brazil, and in montane forest in Central America, the Andes, the coastal ranges of Venezuela and the various ranges of the Brazilian Atlantic Forest. It is also one of few dendrocolaptids that is present on the offshore island of Tobago, although, surprisingly, it is absent from Trinidad.

Only a small number of woodcreepers inhabit predominantly non-forested habitats. The Narrow-billed Woodcreeper is widespread in both savanna (cerrado) and Chaco vegetation in central South America, as well as, more locally, elsewhere on the continent. It also occurs in gallery and dry forests and can even be found in gardens and city parks. Even more plastic in its habitat preferences is the Straight-billed Woodcreeper. This species is largely restricted to coastal mangroves in some parts of its range, but elsewhere it frequents arid scrub, wooded savanna, gallery forest, or seasonally flooded forest. It is equally at home near humans, frequenting plantations, scattered trees associated with agricultural lands, and even trees on the outskirts of some Amazonian cities. The only wooded situation that it avoids is the interior of mature forest. The Streak-headed Woodcreeper fills a similar niche in Central America. It shows a comparable variety of habitat preferences, and appears to be equally comfortable in the proximity of humans. The Scimitar-billed Woodcreeper occurs in arid scrub, savanna, and the Chaco woodlands of southern South America.

Finally, there are four dendrocolaptids that can be found in semi-open woodland. The Great Rufous and Moustached Woodcreepers, in addition to some populations of the Olivaceous Woodcreeper and the Red-billed Scythebill, occur primarily in semi-deciduous and deciduous woodlands, habitats that may be transformed seasonally into semi-open environments.

General Habits
The Dendrocolaptidae are among the most characteristic avian inhabitants of Neotropical lowland forests. Their conspicuous habit of creeping, or “hitching”, up trees gives the group its name. This behaviour converges with that of the generally smaller but morphologically similar certhiid creepers of the Holarctic and treecreepers (Climacteridae) of Australia and New Guinea. In each group, the birds climb up tree trunks and branches by grasping the bark with their strong feet and long claws, and using the spine-tipped tail as a prop. Woodcreepers move with short hops, those of some species being so rapid that motion appears smooth. Although they occasionally move in reverse downwards on trunks, especially when descending into nesting or roosting cavities, or when foraging in association with ant swarms, they typically move upwards and outwards, using a direct or spiral route. Trunk-foraging woodcreepers begin near the bottom of their preferred stratum, creep to the top of this level, and then fly to the base of the next tree in order to repeat the process. Most species prefer vertical trunks, while others select horizontal limbs in the canopy, and a few seem to specialize in creeping along the undersides of branches. Only a small number of species, particularly those frequenting open situations, regularly descend to forage on the ground (see Food and Feeding). The flight of most large woodcreepers is strong but somewhat undulating, with rapid flaps interspersed with glides on outstretched wings and spread tail. Smaller species have a more direct and darting flight.

Woodcreepers are generally encountered singly or in pairs, but many species join the mixed-species flocks that are ubiquitous in the lowland forests frequented by those dendrocolaptids. Woodcreepers usually attend flocks of insectivores, rather than those of tanagers (Thraupidae) and other frugivores. Most of them associate with understorey flocks containing Myrmotherula antwrens and, especially, Thamnomanes antshrikes. A few species, most notably the Lineated Woodcreeper, associate with canopy flocks led by greenlets (Hylophilus) or other canopy-dwelling insectivores. Groups of woodcreepers consisting of more than a single pair are in general uncommon, and in most instances these groups represent families, with one or both parents tending dependent young. In the case of Dendrocincla, only one parent raises the young (see Breeding), so that groups of multiple individuals probably represent either a mother and her offspring or aggregations of wandering immatures. By contrast, the larger woodcreepers of the genera Dendrocolaptes, Hylexetastes and, presumably, Xiphocolaptes remain paired throughout the year, and the young of some species may not become independent until the beginning of the year after hatching; thus, when two individuals of a species are seen together, they probably represent pair-members, while small groups are likely to be family parties.

The aggregations of woodcreepers that gather, sometimes in fairly large numbers, over swarms of army ants are anomalous for these typically solitary birds. Ant swarms are often attended by three or fewer Plain-brown Woodcreepers, although it is not unusual for four or five individuals to be present together, and in Trinidad, in the absence of competing thamnophilid antbirds, up to twelve of this species have been found at the same swarm. Similarly, seven or eight White-chinned Woodcreepers have been noted at ant swarms in south-eastern Peru.

Although not particularly secretive, many woodcreepers are nonetheless shy. Most move rapidly and continuously, making them difficult to observe. Only rarely do trunk-foraging woodcreepers remain motionless for more than a few seconds. By contrast, those that forage over ant swarms are more sedate, primarily because they must wait to spot prey flushed by the ants. Accordingly, a disproportionate amount of what is known of the behaviour of the Dendrocolaptidae pertains to birds foraging in association with ants. At the first sign of danger, woodcreepers hide on the rear surface of large trunks while tentatively peering around to investigate the situation. Many are difficult to approach and to study at close quarters, but some become accustomed to the presence of an observer, especially during extended periods of observation while they forage over army ants.

The roosting behaviour of this family has been studied for only a few species in Costa Rica, by A. F. Skutch, and in eastern Amazonia, by Y. Oniki. Woodcreepers roost solitarily, in cavities similar to the ones used for nesting (see Breeding). Natural cavities are utilized more often than are old woodpecker holes, possibly because they are less conspicuous. The young do not return to the natal nest after fledging, but instead they seek new sites for roosting. Although documented roost-sites have been in cavities relatively close to the ground, this may reflect ease of observation as much as it does availability of suitable cavities or particular preferences. A captive Straight-billed Woodcreeper roosted in an upright position, with its head tucked into its back feathers. This posture is probably the typical one adopted by all roosting woodcreepers.

Maintenance behaviour among the members of this family is poorly known, with most information being only anecdotal. Various woodcreepers scratch the head by the indirect method, reaching over a wing with one foot while gripping the substrate with the other. In addition, many dendrocolaptids have been observed to perform “anting”, in which they rub small, presumably noxious items on the wing or tail feathers; sometimes, the items are then eaten. Anting behaviour is often thought to be a means of removing ectoparasites of the plumage or skin, but Willis suggested that it may serve to wipe distasteful secretions from prey, while H. Sick proposed the possibility that formic acid released during anting may be a physiological stimulant.

Regardless of the true function of anting, and despite a dearth of knowledge of the natural history of the Dendrocolaptidae, woodcreeper parasites are fairly well studied. G. Bennett and colleagues have studied blood parasites in many woodcreeper species. Likewise, R. Price and D. Clayton reviewed an array of feather lice, chiefly of the genus Rallicola, that are known from woodcreeper hosts. Moreover, L. Kudon described a new genus of feather mites, Platyacarus, that is specific to woodcreepers, and detailed host-parasite relationships for many new species in this genus. Within the family, the absence of Platyacarus mites on the Scimitar-billed Woodcreeper provides support for the ancestral position of the genus Drymornis, for these mites infest at least some members of all other dendrocolaptid genera. Finally, M. Marini and D. Couto correlated ecological parameters and ectoparasite infestation for several woodcreepers from central Brazil.

Some woodcreepers are remarkably aggressive towards conspecifics and even towards other woodcreepers. During his studies of ant-followers, Willis documented numerous instances of both intraspecific and interspecific aggression among dendrocolaptids, while N. Pierpont studied interspecific interactions in a guild of woodcreepers occurring in Peru. Not surprisingly, both found that larger species are generally dominant, but some highly aggressive Xiphorhynchus species periodically attack the larger, less agile and possibly somewhat more docile species in the genus Dendrocolaptes. The Buff-throated, Black-striped and Tschudi’s Woodcreepers seem to be especially aggressive. Pierpont speculated that the aggressive nature of Tschudi’s Woodcreeper may be necessar

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