Class AVES Order PASSERIFORMESSuborder OSCINES Family TROGLODYTIDAE (WRENS) free text from the Handbook of the Birds of the World.
- Very small to medium-sized, mostly insectivorous birds with finely pointed and often decurved bill, tail variously long and graduated to extremely short, one species with sturdy legs and bill; plumage colours mostly grey and brown, often with rufous tones.
- 9-22 cm.
- New World, one species also in Eurasia and north Africa.
- Forest, forest edge, scrubland, suburban gardens, marshes, desert brushland, rock faces.
- 17 genera, 85 species, 401 taxa.
- 6 species threatened; none extinct since 1600.
Troglodytidae is essentially a New World family, most diverse in Central America and north-western South America, with only one species, the Northern Wren (Troglodytes troglodytes), having escaped to the Old World. Everywhere, the members of this family are small, highly active, and highly vocal insectivores, perhaps seldom seen but always, it seems, dominating the soundscape.
The relationships of wrens to other avian groups have been debated over the years. In 1881, R. B. Sharpe, in the Catalogue of the Birds in the British Museum, classified the wrens as a subfamily within the Timaliidae, which also included the dippers (Cinclidae). A few years later, the American Ornithologists’ Union, in its 1889 Check-list of North American Birds, included the wrens as one subfamily and the mockingbirds and thrashers (Mimidae) as another within the family Troglodytidae, which it placed just after the wagtails and pipits (Motacillidae) and the dippers, and before the treecreepers (Certhiidae) and the tits and chickadees (Paridae). In 1904, R. Ridgway discussed the long-suspected probability that other songbirds most closely related to the wrens were the treecreepers and the mimids, “not far removed” from the dippers. Ridgway used the relatively high degree of cohesion between the anterior toes to show that the wrens were more like the treecreepers and parids than like the mimids, the latter, which are often referred to as “mimic-thrushes”, being in turn more like the true thrushes (Turdidae). E. Mayr and D. Amadon, in 1951, placed the wrens in the family Muscicapidae, which they subdivided into the seven subfamilies Muscicapinae, Timaliinae, Sylviinae, Malurinae, Turdinae, Miminae, and Troglodytinae. They thereby suggested a relationship with, among others, the Old World flycatchers (Muscicapidae), the Old World warblers (Sylviidae) and the Australasian fairywrens (Maluridae). Another group that has often been associated with the wrens is the nuthatches (Sittidae). In a typical linear classification, Troglodytidae has been placed between the dippers and the mimic-thrushes, as by Mayr and Greenway in 1960, or between the treecreepers and the dippers, as by Ridgway in 1904.
In more recent decades, the data obtained by C. G. Sibley and J. E. Ahlquist from studies involving DNA-DNA hybridization suggested a novel hypothesis for the relationships of wrens. Their results indicated that the wrens, including the highly unusual Donacobius (Donacobius atricapillus), were the sister-group to the gnatcatchers (Polioptila), the gnatwrens (Microbates) and the Verdin (Auriparus flaviceps). The first two of these groups had traditionally been located within the subfamily Polioptilini of the Muscicapidae, while the Verdin had been included with the penduline tits in the family Remizidae. Furthermore, Sibley and Ahlquist suggested that the wrens, the gnatcatchers and the Verdin together formed a sister-group to the treecreepers of the genera Certhia and Salpornis, and proposed that they all be combined into a single family, the Certhiidae. This family, thus expanded, was a sister-group to Sittidae, which comprises the nuthatches (Sitta) and the Wallcreeper (Tichodroma muraria). In addition, these genetic data emphasized the groups to which the wrens appeared not to be closely related: the babblers, which were moved to the family Sylviidae, the mimic-thrushes, which were found to be a sister-group to the traditional starling family Sturnidae, placed in another superfamily, and the dippers, forming yet another superfamily.
These recent ideas concerning the relationships of wrens received considerable support from a subsequent genetic analysis undertaken by F. H. Sheldon and F. B. Gill, whose results were published in 1996. It was agreed that the wrens’ closest relatives are the gnatcatchers and gnatwrens, the treecreepers and the nuthatches. These authors’ data also supported Sibley and Ahlquist’s hypothesis that the mimic-thrushes and Sturnidae, the starlings, are sister-groups, well separated from the wrens. The Verdin, however, remained with the penduline tits.
Many of these proposed relationships were, in turn, corroborated in 2002 by F. K. Barker and colleagues, and they seem now to be generally accepted. Thus, the sister-group to the wrens is Polioptila, and the two together are sister to the treecreepers. Somewhat less certain is that all of these birds are the sister-group to the nuthatches. Further, all of these groups appear together to represent a sister-group to a clade that includes the dippers, the starlings, the mimic-thrushes, the thrushes of the genus Turdus, and the Old World Muscicapa flycatchers.
Over the last century or so, the family itself has largely been accepted as comprising a cohesive, monophyletic group of species, once several members of the Timaliidae and the Sylviidae were removed. The one remaining problem, however, concerns the Donacobius, a puzzling marsh-nesting bird found throughout most of lowland tropical South America. Details of its anatomy, social structure and behaviour (see General Habits) have suggested that it is either a wren or a mimic-thrush, and classifications over the years have alternately placed this species in either the Mimidae or the Troglodytidae. One of the last public statements, in 1982, declared that the Donacobius is a wren, and not a mimid, a view based on a still unpublished study of pterylosis by M. H. Clench and colleagues. That declaration was accepted by the American Ornithologists’ Union in 1983. A year later, the genetic data of Sibley and Ahlquist indicated that the Donacobius was, in fact, as genetically distant from the wrens as it was from the mimic-thrushes, although, somewhat surprisingly, Sibley and Ahlquist used this equivocal information to place the Donacobius among the wrens. More recent genetic analyses by Barker, however, suggest that this species is neither a wren nor a mimid but, rather, a unique “sylvioid”, a group that includes the babblers and the Old World warblers, as it clusters close to Prinia and Zosterops.
For the time being, it is deemed best to retain the Donacobius among the Troglodytidae, pending its “official” transfer to a more appropriate taxonomic position.
Less effort has been expended in trying to determine the relationships among the genera within the wren family. Some debate has centred on the genera Hylorchilus, Catherpes and Salpinctes. In 1904, for example, Ridgway accepted all three genera, but in 1960 Mayr and J. C. Greenway placed the Canyon Wren (Catherpes mexicanus) with the American Rock Wren (Salpinctes obsoletus) in the genus Salpinctes. Sumichrast’s Wren (Hylorchilus sumichrasti) was originally described in the genus Catherpes back in 1871, and then moved to Hylorchilus in 1897, although, 90 years thereafter, J. W. Hardy and D. J. Delany argued that, on the basis on vocal similarities, it should be returned to Catherpes. A vocally distinct former subspecies of Sumichrast’s Wren was elevated to full species status in 1993, becoming Nava’s Wren (Hylorchilus navai), and thereby providing a small point in favour of keeping these two closely related wrens in their own separate genus, Hylorchilus.
A recent survey of the wrens in the genus Troglodytes, carried out by N. H. Rice and colleagues, is consistent with some suspected relationships, but it also offers some surprises. Most of all, it encourages further study not only of this genus but also of others within the family, especially the speciose Thryothorus. The genetic data obtained by Rice and co-workers indicate, not surprisingly, that the Northern House Wren (Troglodytes aedon), the Southern House Wren (Troglodytes musculus) and the Brown-throated Wren (Troglodytes brunneicollis) represent one major clade and, perhaps less expectedly, that the Rufous-browed Wren (Troglodytes rufociliatus) is a sister to this clade; in their analysis, the two house wrens are sister-taxa. An association of the same group of three species had been found in the analysis made just a few years earlier by R. T. Brumfield and A. P. Caparella, but these authors concluded that the Northern House Wren and the Brown-throated Wren were sister-taxa, a disagreement that will have to be settled through further analyses. Another major clade identified by Rice and colleagues included the Mountain (Troglodytes solstitialis), Tepui (Troglodytes rufulus) and Ochraceous Wrens (Troglodytes ochraceus). Surprisingly, the sister-group to these two clades was the Timberline Wren (Thryorchilus browni), and the Northern Wren fell well outside this grouping and was considered sufficiently different to be placed alone in a monotypic genus, Nannus. These various hypotheses of relationships are intriguing, but they are based on relatively limited genetic sampling, and the true relationships of these species to one another must remain a mattter of debate until further study is undertaken.
The only other proposed relationships among wren genera are those implied in various linear classifications, such as the sequence that is used in the present treatment. In such linear sequences, the genera Troglodytes and Thryorchilus, for example, are placed together, implying that they are closely related, but few data exist to support one linear classification over another.
Further genetic analyses, such as those by Barker, are likely to clarify relationships among the genera. In his thorough study, Barker drew genetic samples from 20 species among the traditional Troglodytidae, and from all genera except the monotypic Ferminia, Thryorchilus and Uropsila, although, as implied in the preceding paragraphs, Thryorchilus is assumed to be closely allied to Troglodytes. This study also incorporated close relatives of the wrens, such as treecreepers, nuthatches, mimids and a gnatcatcher, as well as several more distantly related species.
Barker’s results conflict with the traditional linear series of genera, which had hitherto been the “best guess” of a sequence listed from “primitive” genera to “derived” ones. For example, although traditional linear classifications place Campylorhynchus first, and even within its own subfamily, these wrens are clearly not the sister-group to all other wrens, and phylogenetic trees show them nested well within, rather than basal to, the other troglodytids. In addition, such linear series place at the end those genera that tend to be ground-oriented, including Thryorchilus, Henicorhina, Microcerculus and Cyphorhinus, but this group is polyphyletic. Thryorchilus belongs to a clade that also includes Cistothorus and Troglodytes, while Microcerculus may be part of a basal radiation within the family, and Henicorhina and Cyphorhinus are sister-taxa, which in turn are probably sister to most Thryothorus.
Barker also concluded that Hylorchilus and Catherpes are sister-taxa, a result consistent with arguments based on similarity of song between the Canyon Wren and Sumichrast’s Wren, with the distinct songs of Nava’s Wren secondarily derived. It is possible that the sister-group of these wrens is the similarly petrophilous (rock-dwelling) American Rock Wren, which would permit all four of these species to be combined in the same genus, but other data suggest that Salpinctes, the rock wren, may be basal to all other wrens.
One of the more controversial of Barker’s hypotheses is that the Carolina Wren (Thryothorus ludovicianus) is a sister-taxon to Bewick’s Wren (Thryomanes bewickii), the two being sister-taxa to the Campylorhynchus wrens. A discovery that Thryothorus is polyphyletic, with, for example, Thryomanes nested within it, would not be so surprising in view of the large number of species currently contained in this little-studied genus, but the removal of the Carolina Wren to so distant a location is a rather novel hypothesis.
House Wren feeding young Shiny Cowbird, Wanica, Surinam. Picture by Jan Dolphijn
Clearly, these genetic data provide hypotheses for relationships that are worthy of further testing. Moreover, and above all, it is important to realize that the above-mentioned ideas are largely hypothetical, representing what are currently the best guesses based on limited data. It may be hoped that further research work will significantly clarify these relationships.
Research on vocalizations (see Voice) has suggested that recognition of additional species within the Troglodytidae may be warranted. The Marsh Wren (Cistothorus palustris), for example, consists of highly differentiated eastern and western populations in North America, as also does the Northern Wren, the Old World population of which may represent a further one or more species. As revealed by D. E. Kroodsma and co-workers, the Sedge Wren (Cistothorus platensis), too, exhibits substantial variation in plumage, vocal behaviour and style of song development, and habitat selection (see Habitat) within its large range, which extends from North America down through South America, and it is almost certain that more than one species is involved.
So far as the Marsh Wren is concerned, not only do the eastern and western populations differ in many perceivable ways, many of these differences being based on genetic differences, but they also occur together in the same marshes in central Saskatchewan, where interbreeding between them is limited. Eastern and western males defend territories against one another, and analysis of mitochondrial DNA in the population largely reveals two types of wren, one eastern and one western, with little interbreeding. If they interbred freely, then one would expect a genetically homogeneous population of Marsh Wrens in this transition zone, but the two types of wren signal that they themselves distinguish each other as two species.
Another currently recognized species in which songs provide clues to past evolutionary history is the Northern Wren. In North America alone there are two strikingly different singers, again separated along east-west lines. Eastern and boreal males occur from Nova Scotia south to North Carolina, and west at least to Michigan and Minnesota, while western males have been documented from British Columbia south to California; it is not known where these two types of singer meet, if they do at all. In addition, the songs of Northern Wrens in the Old World are different from those in North America.
On the basis of singing behaviour alone, the emerging hypothesis is that the western Nearctic and eastern Nearctic Northern Wrens diverged first, followed by a divergence of eastern Nearctic wrens and Palearctic wrens. This hypothesis is now supported and enhanced by the work of Drovetski and co-workers, who analyzed the genomic DNA from 97 wrens from throughout North America and Eurasia. These authors estimate that the western Nearctic wren diverged from the Holarctic ancestor roughly 1Â·6 million years ago, and that the Holarctic ancestor diverged into eastern Nearctic wrens and Palearctic wrens about one million years ago. Within Eurasia, four more groups are now identified, having originated as follows: eastern and western Palearctic wrens diverged about 0Â·83 million years ago, and then each respective population diverged one more time, between 0Â·54 million and 0Â·67 million years ago. The proliferation of these groups thus occurred during the early and middle Pleistocene glaciations. How many species occur in this Holarctic distribution depends on one’s definition of a species, but the best guess is that at least three should be recognized, two in North America and one in Eurasia, and that perhaps each of the four clades in Eurasia could also be recognized as a full species.
Very recently, differences in songs among supposed Grey-breasted Wood-wrens (Henicorhina leucophrys) were used in helping to identify a new species in the western Andes of Colombia. This new species, the Munchique Wood-wren (Henicorhina negreti), is found only at high elevations on the Pacific slope, in the extremely wet, stunted cloudforest that is almost continuously shrouded in fog. In the taller forest at lower elevations on the west slope, it is replaced abruptly by the Grey-breasted Wood-wren of the subspecies brunneiceps, and on the drier east slope by the nominate race of the latter. Compared with the adjacent populations of Grey-breasted Wood-wrens, the Munchique Wood-wren has a more distinctly barred abdomen, a darker juvenile plumage, relatively longer tarsi and a proportionately shorter tail.
It is likely that, were it not for the fact that these wrens learn their songs and therefore have geographically differentiated song dialects (see Voice), far more species of wren would be recognized. New species are rather routinely described for various suboscines, such as the tyrant-flycatchers (Tyrannidae), the songs of which are not learnt and therefore represent a vocal signature for the genotype of the bird; in the case of Thamnophilus punctatus, another suboscine that presumably does not learn its songs, M. L. Isler and colleagues have suggested that what was previously considered a single species, the Slaty Antshrike, in fact consists of six or more species. Most species of songbird, however, offer no such obvious vocal clue as to how their populations are differentiated, and the conservative approach is therefore to keep the highly differentiated Northern Wrens in one species. The same reservations apply to the Marsh Wrens and the Sedge Wrens and, no doubt, to other troglodytids, too. Nevertheless, future research will surely lead to the elevation to species rank of a good number of these behaviourally and vocally distinctive taxa. Indeed, very recently published work suggests that the globally threatened Apolinar’s Wren (Cistothorus apolinari) of Colombia may, in fact, consist of two species, differentiated not only morphologically and by habitat preference but also by song. One form, currently described as the subspecies hernandezi, not only has a different song from the nominate race, but additionally, and in contrast to the latter, indulges in communal group song, both antiphonal and in duet.
Wrens are generally small birds. In fact, in the New World, only some of the hummingbirds (Trochilidae), kinglets (Regulus), gnatcatchers and parulid warblers are lighter in weight than the smallest wrens. The largest member of the family, the Giant Wren (Campylorhynchus chiapensis) of southern Mexico, is a giant only in comparison with its relatives. With a length of 22 cm and weighing up to 57 g, it is about the size of a smallish thrush. At the opposite extreme, the Sedge Wren is about 9 cm long, and the Northern Wren weighs as little as 6 g. Birds’ weights do, of course, vary greatly according to the condition of the individual.
Winter Wren, Brostowo, Poland. Picture by Jan Dolphijn
None of the troglodytids is brightly coloured in plumage, and reds, bright yellows, greens and blues are entirely absent in the family. Instead, all wrens are various shades of brown or rufous, often with areas of black and white. Despite this modesty of coloration, some species, particularly in the genus Thryothorus, have very attractive patterns of plumage, especially around the head and chest. One feature characteristic of virtually all wrens, and largely absent in most other passerines, is the predominance of barring on both the remiges and the rectrices. This usually takes the form of narrow alternating sections of blackish or dark brown and lighter brown on the outer webs of the primaries and secondaries; the tertials and the rectrices are typically barred on both webs. In a few species, especially the ground-dwelling wrens inhabiting thick, wet, dark tropical forest, the barring is very muted or almost absent, but, on close examination, traces are still discernible, suggesting that the ancestral wrens were barred. The plumage of wrens tends to be soft and rather fluffy.
Most members of the family have twelve rectrices, although the Timberline Wren, the two members of the genus Hylorchilus and the enigmatic Zapata Wren (Ferminia cerverai) have only ten. The rectrices tend to be rounded, with the outer ones often significantly shorter than the central ones. The tail length differs widely among genera. In the genus Odontorchilus, containing two South American species that appear to be converging evolutionarily with the unrelated Polioptila gnatcatchers, birds of similar habits and lifestyle, the tail accounts for almost half of the bird’s total length. In the cactus wren group, the genus Campylorhynchus, it is almost as long in relative terms. More usually, however, the tail is shorter, and in some genera much shorter. The Northern Wren, for example, has a tail that makes up only 25-28% of the total body length. The most extreme instance, however, is that of the ground-dwelling Microcerculus wrens, which appear almost tailless in the field, the rectrices being typically no more than one-fifth of the total length of the bird. This is a further example of convergent evolution, in this case with the small Grallaricula antpittas in the antbird family (Formicariidae), the habitat and habits of which they share.
All wrens have ten primaries. Although the tenth primary, the outermost, may be much reduced, it is always present. They have relatively short and rounded wings, with usually the middle primaries, P5 to P7, the longest. The primaries of some species, when spread out, seem almost to describe an arc of a circle. The wing shape has clearly evolved for a lifestyle centred around short flights in dense vegetation, rather than for aerodynamic efficiency. Notwithstanding this, some species, notably the Northern Wren and the Northern House Wren, undertake long migratory journeys (see Movements).
There is no sexual dimorphism in wren plumages. Males and females are essentially identical in virtually all cases. In addition, there is frequently little distinction between adults and young. In some members of the genus Campylorhynchus and a few of the genus Thryothorus, juveniles do differ markedly in plumage from the adults of the species, but in most genera the distinctions between adult and young plumages tend to be minor and subtle.
Although the troglodytid bill tends to be long and often substantially decurved, considerable variation exists within the family, the bill morphology being dependent on lifestyle and food preferences. Some genera, such as Salpinctes and Troglodytes, have a very fine bill. Members of Catherpes and Hylorchilus, two genera specializing in foraging on rock faces, have a bill that is especially fine and decurved; they also exhibit several other specific modifications, including a flattened skull, for obtaining prey from crevices in rocks. The two Odontorchilus wrens have a very fine bill with a peculiar little notch, of unknown function, two-thirds of the way down the cutting edge of the upper mandible. In the genus Campylorhynchus, several species of which include major quantities of hard vegetable matter as well as large, well-armoured arthropods in the diet, the bill may be quite heavy and powerful. Some members of this genus, such as the Band-backed Wren (Campylorhynchus zonatus), appear to specialize in probing for prey in epiphytes and, consequently, have a longer, finer bill.
The most peculiar bills in the family are found in the ground-dwelling genus Cyphorhinus. The bill is quite stout and powerful, with a curious upper mandible compressed into a sharp, wedge-shaped ridge along the upper surface, giving an odd “Roman-nose” appearance. The precise function of this character is not known. Another unique feature of this genus, shared with many other, totally unrelated South American suboscine passerines, is a patch of bare, coloured skin around the eye.
Rictal bristles are present in some troglodytid genera, such as Campylorhynchus, Henicorhina and Uropsila. In some cases, as in the three Cyphorhinus species and some Thryothorus wrens, they may be very short or unobvious, but in many genera, including Troglodytes, Cistothorus, Salpinctes, Catherpes, Hylorchilus and Microcerculus, rictal bristles are obsolete or absent.
As may be expected for a group of birds that spends most of its time in foraging near the ground, the legs and feet of wrens tend to be substantial in proportion to the small size of the birds, and in some cases they are rather heavy and powerful, with large claws. In contrast, the legs and feet of the canopy-dwelling Odontorchilus wrens are quite fine and dainty.
Finally, one species currently included in Troglodytidae, but almost certainly belonging elsewhere (see Systematics), differs in several respects from the “true” wrens. In general external appearance, the Donacobius resembles the mimids more than it does any wren. The wings are powerful and rather rounded, with very short primaries, and the tail is long and very graduated, almost fan-shaped in fact, with the outer rectrices much shorter than the central ones. The legs are long and very robust, and the bill is long and sturdy, with rictal bristles present but not very obvious. A unique feature of the Donacobius is the presence of a patch of bare yellow to orange skin on each side of the neck, not usually visible in the field, but distended during display.
Information on moult sequences is generally lacking for the great majority of wren species, namely those occurring in Central and South America; this would be a very fertile and productive area of study. More data are available for those species found in North America and Europe. Typically, the first moult that a bird undergoes, that in which it renews the original feathers that it grew as a nestling, occurs within a few months of fledging and is incomplete. The body feathers are replaced, but usually only some flight-feathers are renewed. The extent of this moult is variable, not only among species but also among different individuals of a single species. In Bewick’s Wren, for example, some individuals replace no tail feathers at all in the first moult and some replace all of them, but about two-thirds of individuals replace only some of the rectrices. The more southerly races of this species tend to renew more feathers than do the northern ones. Among wrens, the replacement of the remiges in this first moult is frequently incomplete and often eccentric; rather than starting at the outermost or innermost primary or secondary and proceeding inwards or outwards in sequence, it begins several feathers in, thereby producing a mixture of old and new feathers in patches. In subsequent years, the prebasic moult of all North American wrens is complete.
Most wrens do not undergo a pre-breeding moult, a spring moult that in some families, such as the parulid warblers, results in a characteristic bright breeding plumage. The exceptions to this are the Cistothorus wrens, which have a partial moult before breeding. In the case of the Sedge Wren, this results in the replacement of a variable number of greater wing-coverts, tertials and rectrices, but not, apparently, of the primaries or secondaries. A similar pattern is found in the Marsh Wren.
As a family, the wrens have been highly successful in adapting to a very wide range of habitats, occupying a variety of ecological niches which, in continents other than the Americas, are taken up by several different avian families.
The largest wren genus is Thryothorus, which has the greatest density of species occurring in southern Central America and north-western South America. Within this one genus there is a considerable diversity of habitat requirements, as may be expected since its members are found all the way from southern Canada south to Bolivia, but, in broad terms, all require areas of trees with substantial undergrowth. Some species, such as the Banded Wren (Thryothorus pleurostictus) and the Happy Wren (Thryothorus felix), are found in dry forest and bushland. The majority, however, favour more humid habitat, while some, such as the Bay (Thryothorus nigricapillus), Riverside (Thryothorus semibadius) and Coraya Wrens (Thryothorus coraya), show a preference for the vicinities of actual watercourses. Thryothorus wrens tend to live more at forest edge than in deep unbroken forest, doubtless owing to the presence of denser undergrowth in areas exposed to sunlight. Consequently, several members of the genus, such as the Plain Wren (Thryothorus modestus), have thrived in somewhat disturbed habitat where climax forest has been partially cut over or allowed to regenerate. Sometimes, there is an apparent division of habitat utilization between two species. In Colombia, for example, the Bay Wren tends to occur at forest edge, being replaced in the deeper interior by the Sooty-headed Wren (Thryothorus spadix), while in western Mexico a frequently sympatric pair of species, the Happy and Sinaloa Wrens (Thryothorus sinaloa), may have slightly different requirements, the latter being able to tolerate sparser woodland. Some species are largely associated with specific vegetation; among these are the Plain-tailed (Thryothorus euophrys) and Inca Wrens (Thryothorus eisenmanni), which usually occur in areas with Chusquea bamboo. Typically, the Plain-tailed Wren is the first colonist of highly disturbed land, such as landslips in the precipitous Andes, a habitat which is mimicked by spoil slopes from road construction. In Bolivia, Moustached Wrens (Thryothorus genibarbis) are often found in Bambusa bamboo, whereas Heliconia thickets in Costa Rica are the preferred habitat of both the Bay Wren and the Black-bellied Wren (Thryothorus fasciatoventris). Because of their preference for secondary growth, many species in this genus have survived, or even prospered, with man-made habitat change. The Stripe-breasted Wren (Thryothorus thoracicus) in Costa Rica has adapted well to cacao plantations at low altitudes and to shade coffee plantations at higher elevations.
The only temperate-zone Thryothorus, the Carolina Wren, which, according to recent studies, may not really belong in this genus (see Systematics), lives largely in highly modified habitats, such as abandoned farmland and well-vegetated suburbs. Its natural habitats included oak (Quercus) hardwoods and mixed woodlands of oak and pine (Pinus) having a variety of other tree species, such as hickory (Carya) and cottonwood (Populus). The two insular subspecies of the Carolina Wren, burleighi and nesophilus, are found in slash pine (Pinus elliottii) and palmetto stands.
In contrast to Thryothorus, the highly terrestrial members of the genus Microcerculus are much more restricted to undisturbed virgin lowland humid forest, and do not take at all well to habitat modification. The opening-up of the forest canopy induces lower-level growth unsuitable for these wrens. The four Microcerculus species are generally found at lower altitude, usually from sea-level to 1500 m, although the Flutist Wren (Microcerculus ustulatus) is a more montane species, being encountered at up to 2100 m on tepui summits in Venezuela.
Four troglodytids are closely associated with rocks. Ironically, the American Rock Wren exhibits the least morphological adaptation to this habitat, not differing greatly, in external form, from members of the genus Thryothorus. It occurs in habitats that range from fairly dry to very arid, and is usually to be seen in barren rocky places, including scree slopes, boulder falls and areas of bare, sunbaked mud. It will take advantage of mining and quarrying activities, occurring in areas of spoil and tailings, as well as colonizing areas temporarily made bare by clear-cut forestry. As a vagrant, with records over much of eastern North America, the American Rock Wren is often found in artificial situations which resemble its preferred habitat, such as concrete structures.
The three other rock-dwelling species are truly petrophilous, being associated with rock faces and showing major morphological adaptations to exploit this niche. Canyon Wrens are, indeed, associated exclusively with canyons, rock faces and, in California, sea-cliffs. Given this requirement, this species is quite catholic in its habitat choice, occurring in cool uplands at up to 3000 m, in dry oak-wood canyons or, in southern Mexico, in humid areas as low as 200 m. In contrast, the two members of the genus Hylorchilus are very specific in their habitat requirements and, as a consequence, have highly restricted geographical ranges. Both Sumichrast’s and Nava’s Wrens are found solely in forested karst limestone outcrops. The former can tolerate some slight changes to the forest cover, including the planting of shade coffee, since this does not impinge on the rock faces where it feeds, but for Nava’s Wren any disturbance seems to be unacceptable.
Some wrens have radiated into marshland and swamp, exploiting niches that in the Old World are occupied mainly by various warbler genera of the family Sylviidae. The four species of Cistothorus have all specialized in wet, mostly monocotyledonous habitat of varying types. The Marsh Wren, as a breeding species, is usually confined to vegetation over standing waters, normally cat-tails (Typha), bulrushes (Scirpus) and reeds (Phragmites) in northern freshwater marshes, and cordgrass (Spartina) and sedges (Juncus) in brackish coastal marshes. Northern interior populations spend the winter in other fresh and brackish marshes, in the latter case frequently co-existing with resident, non-migrating individuals of the species. The Sedge Wren, on the other hand, in North America, usually avoids areas of standing water, preferring damp sedgy meadows, often with small bushes, although it may occur also in weedy rice paddies in the southern United States. In its extensive South American range, however, this wren’s habitat varies enormously, from cold pÃ¡ramo in the Andes to open grassy savanna in Venezuela, dry cerrado grassland in Brazil, wet alder (Alnus) forest and bamboo bogs in Colombia, the borders of tidal marshes in Argentina and tussac grass in the Falklands. The great diversity of habitat occupancy, along with vocal differences, gives support to the argument for the separation of South American forms taxonomically from those in North and Central America (see Systematics).
The two subspecies of Apolinar’s Wren differ markedly in their habitat requirements. The nominate race lives in similar lake-edge habitat to that occupied by the Marsh Wren, namely reedbeds dominated by cat-tails and bulrushes, albeit at altitudes of 2500 m to slightly over 3000 m. In contrast, the race hernandezi occurs higher up, between 3800 m and 3900 m, in boggy pÃ¡ramo with low shrubs and a hirsute leafy ground plant known locally as “frailejÃ³n” (Espeletia grandiflora).
Restricted to a very small area of Cuba, and one possessing a unique habitat, the enigmatic Zapata Wren has very specific habitat requirements. These are savanna-type swamp with sawgrass (Cladium jamaicense) and rushes, and with some bushes which can be used as songposts. The water level in the Zapata Swamp is quite variable, but the Zapata Wren tends to live in drier areas, which allow it to forage on the ground.
Another wetland-dwelling species currently included within the family is the Donacobius. This relatively large bird, of uncertain taxonomic affiliation (see Systematics), inhabits brushy vegetation along riversides and the overgrown margins of water impoundments in the lowlands of tropical South America. Although it sometimes forages away from such areas, it invariably nests only in marshy vegetation.
In North America, the Northern Wren occurs in such boreal-type habitats as moist coniferous forest with extensive underbrush, but also in mixed hardwood-conifer stands. In addition, it is also found, in an extensive range of subspecies, on treeless or nearly treeless oceanic islands in the Aleutian chain. The same species, having invaded the Old World via the Bering bridge, has, in the absence of competition from other troglodytids, expanded into a catholic range of habitats in three continents. In western Europe, the most favourable habitat is damp woodland, either deciduous or mixed, with extensive undergrowth, but the species is also common in suburban gardens, in moorland scrub and on oceanic islands with scanty vegetation. In other parts of its Old World range it may be more restricted, as, for example, in the Atlas Mountains of Morocco, where it is largely confined to stream valleys and forests at altitudes between 1200 m and 1800 m; in Nepal, it is found at elevations of 2500 m to 4800 m.
In the Americas, the “house wren superspecies” (see Systematics) occupies many of the ecological niches exploited by the Northern Wren in the Palearctic Region, especially highly modified landscapes such as wood edges, well-vegetated suburban areas and regenerating abandoned farmland. The Southern House Wren, being unable to tolerate unbroken forest, does not occur over much of Amazonia, but it rapidly colonizes suitable clearings when they appear. Over the remainder of the continent, this species occupies a remarkable range of habitats, from quite highly urbanized situations to montane areas and arid regions with dry bushland, from sea-level up to 4000 m. In the Falkland Islands, the isolated Cobb’s Wren (Troglodytes cobbi), obviously closely related to the mainland house wrens, has adapted to a harsh environment consisting of moorland and the tussac grass Paradiochloa; unlike any other troglodytid species, it has learnt to forage among seaweed on tidal shores, and it does in fact occur at higher densities in places where territories actually abut the sea. In contrast to the house wrens, the group of montane Troglodytes wrens occurring from southern Mexico southwards to northern Argentina is much more specific in its habitat requirements. This group, comprising the Mountain, Santa Marta (Troglodytes monticola), Ochraceous, Rufous-browed and Tepui Wrens, is usually restricted to various forest types, always in uplands and often at considerable altitude, in the case of the Santa Marta Wren up to 4800 m. Similar habitat, that of bamboo thickets in pÃ¡ramo and sub-pÃ¡ramo, is required by the appropriately named Timberline Wren.
Bewick’s Wren often co-exists with, and perhaps suffers from competition from, the Northern House Wren in eastern North America. Here, it has benefited from European colonization, as semi-open habitat was created by the clearing of climax forest for farmland. In western North America, it occupies a very wide variety of habitats, including chaparral brushland, cactus-dominated scrub and riparian woodland, some of which are unsuitable for house wrens.
Forming a group of four closely related species, the wood-wrens are found in forested land from Mexico south to Bolivia. Notwithstanding their great morphological and behavioural similarities, they have developed distinct habitat requirements and only rarely occur together. The White-breasted Wood-wren (Henicorhina leucosticta) inhabits wet lowland broadleaf forest, mostly below 1500 m, whereas the Grey-breasted Wood-wren lives in humid mountain forest, usually above 1500 m, and extending up to pÃ¡ramo edge at 3800 m in Costa Rica. The Bar-winged Wood-wren (Henicorhina leucoptera) is found very specifically in a few high-altitude forests, usually very impoverished, with stunted trees and heavy ericaceous undergrowth, on leached quartzite soil, a habitat which it sometimes shares with the previous species. The fourth species, only recently distinguished as a separate species from the Grey-breasted Wood-wren (see Systematics), is the Munchique Wood-wren, which has hitherto been recorded only at 2250-2640 m in extremely wet, stunted cloudforest on the Pacific slope of the Colombian Andes. It is ecologically sharply separated from the two neighbouring subspecies of the Grey-breasted Wood-wren, one of which lives at lower elevations on the same slope, while the other occurs on the drier eastern slopes of the Munchique massif. Although all three taxa can be seen within a distance of 1 km in some areas, no two of them have ever been found together.
The genus Cyphorhinus contains three species which, in appearance and habits, seem to be evolving convergently with the terrestrial antbirds, the habitat of which they frequently share. All occur in wet forest with extensive undergrowth. One, the Chestnut-breasted Wren (Cyphorhinus thoracicus), is a montane form, found in wet upland forest and cloudforest, often with a luxuriant growth of mosses and epiphytes. The other two, the Song Wren (Cyphorhinus phaeocephalus) and the Musician Wren (Cyphorhinus aradus), are lowland species, inhabiting humid forest and second growth with an extensive understorey, or vÃ¡rzea, from sea-level to 1000 m.
In the Andes, from Colombia southwards to northern Bolivia, the four species in the genus Cinnycerthia are very similar to one another not only in appearance but also in habitat requirements. All are found in wet mountain forest with a luxuriant understorey, usually between 1500 m and 3500 m, and often in association with thickets of Chusquea bamboo or in areas with extensive wet mosses growing epiphytically on tree boles and low branches. This genus as a whole does not tolerate extensive habitat modification.
The two Odontorchilus species are unusual among wrens in that they feed mostly in the forest canopy. As a consequence, both are restricted to areas of suitable forest, usually those which have not undergone much human modification. The Tooth-billed Wren (Odontorchilus cinereus) is a lowland species, found in tropical Amazonian forest below 500 m, while the Grey-mantled Wren (Odontorchilus branickii) lives in humid montane upper-tropical and subtropical forest of the Andes from Colombia south to Bolivia. The latter lives at 1400-2200 m on the Amazonian drainage, but can be observed as low down as 800 m on the Pacific slope.
The large wrens in the genus Campylorhynchus have succeeded in colonizing some habitats which are denied to smaller members of the family. No other troglodytid genus has been so successful in arid areas of Mexico and the south-western United States, although several other small insectivorous birds from different families, such as the Verdin and the gnatcatchers, have managed to exploit very arid landscapes. The Cactus Wren (Campylorhynchus brunneicapillus) occurs in a number of different types of desert, although always with the proviso that there be spiny cacti, such as prickly-pear (Opuntia) or various species of cholla (Opuntia), in which to nest. In the absence of such cacti, as, for example, in uniform stands of mesquite bushes (Prosopis), the Cactus Wren is generally absent. Cactus Wrens adapt quite well, albeit at a lower density, to highly degraded and disturbed habitats, including such areas as gravel pits and junkyards, so long as sufficient suitable vegetation remains for foraging and nesting.
Several other members of the genus, such as the Fasciated (Campylorhynchus fasciatus) and Boucard’s Wrens (Campylorhynchus jocosus), also specialize in semi-arid habitats, although none has been able to exploit true desert to the same degree as has the Cactus Wren. A number of species, such as the Grey-barred Wren (Campylorhynchus megalopterus), are found at higher altitudes in Middle America, when their habitats include pine and pine-oak forest. The Rufous-naped Wren (Campylorhynchus rufinucha) occurs mostly on the drier Pacific slope, where it is frequently associated with bull’s-horn acacias (Acacia collinsii and A. cornigera). These trees are host to aggressive symbiotic ants of the genus Pseudomyrmex, which provide the nesting wrens with vicarious protection from predators such as white-faced capuchin monkeys (Cebus capucinus) (see Breeding). In other parts of Middle and South America, species of Campylorhynchus have adapted to much more humid forest, where they may specialize in foraging in epiphytes, plant forms that are generally absent in arid areas. Troglodytids occurring in such humid biotopes include the White-headed Wren (Campylorhynchus albobrunneus) and the Band-backed Wren, although, in areas where the two are sympatric, the former tends to be found in the wetter habitats. The Band-backed Wren is, in fact, a very adaptable species, occurring in a wider range of habitats than does any other member of the genus; it inhabits humid forest at sea-level in Mexico and Guatemala, palm groves, wet epiphytic and drier pure oak forest at intermediate altitude and, at 3000 m, cypress (Cupressus) forest. It can also tolerate substantially disturbed habitat, such as forest clearings and clumps of trees bordering farmland.
Winter Wren, Bronnesund, Norway. Picture by Jan Dolphijn
Among the different groups of wrens there is a considerable diversity of habits. The great majority of the species are found in forest of various types or at forest edges, mostly in tropical areas. These are complex biotopes, with several different ecological niches, the exploitation of which by different troglodytid genera has given rise to quite diverse behavioural patterns. Several groups of wrens keep on or close to the ground. The most highly terrestrial are the Microcerculus nightingale-wrens, which spend most of their time on the forest floor, walking with a mincing gait, constantly teetering the tail in the manner of an Ovenbird (Seiurus aurocapilla). Nightingale-wrens fly only infrequently, and they are rarely caught in mist-nets, as they simply walk underneath them. In both behaviour and external appearance they are obviously converging evolutionarily with a group of small formicariids, the antpittas, the habitat of which they share. Almost equally terrestrial are the Cyphorinus wrens, which forage on or near the forest floor and which, again, share many morphological characteristics with the unrelated terrestrial antbirds.
Wrens enjoy a reputation for furtiveness. Indeed, the majority of species are relatively difficult to observe, as they readily disappear into dense vegetation at the slightest disturbance. The Microcerculus wrens have developed this behaviour to a fine art and can be extraordinarily difficult for even the most patient watcher to see. By contrast, the large wrens of the genus Campylorhynchus are raucous, boisterous and extrovert birds, frequently singing from exposed posts, in suburban areas even from the tops of lampposts, and generally acting in a rambunctious and uninhibited fashion, travelling in noisy groups that are very easy to locate. In terms of general behaviour, however, most members of the family fall somewhere in between these two extremes. Species such as Sumichrast’s Wren can be very secretive, but frequently are overcome by a sense of curiosity that impels them to emerge in order to sneak a look at the intruder. Without their loud and persistent songs, many wren species, especially those inhabiting dense tropical forest, would go largely undetected.
The wrens living in temperate climates tend to be solitary or to occur in pairs, the young associating with their parents for only a limited period of time. Among tropical genera the situation is more variable. The genus Cinnycerthia is notably gregarious. The Rufous Wren (Cinnycerthia unirufa), for example, occurs in parties of up to 20 individuals, more than can be accounted for by an extended family, and frequently joins mixed flocks with other species. Several other tropical wrens occur in mixed flocks, as typified by the two Odontorchilus species, the Tooth-billed and Grey-mantled Wrens, which frequently associate with mixed parties of tanagers (Thraupidae), becards (Pachyramphus) and other canopy-dwellers. Similarly, the Stripe-throated Wren (Thryothorus leucopogon) routinely occurs in mixed flocks of antwrens (Thamnophilidae) and other species, whereas several of its congeners, such as the Plain-tailed Wren, apparently never do so. Some species routinely follow swarms of army ants (see Food and Feeding). For species with co-operative nesting strategies, notably the tropical members of the genus Campylorhynchus, groups of blood-relatives associate and act collaboratively to defend the nest and rear the young (see Breeding).
A few troglodytids, such as the Marsh Wren, will sing at night, especially in moonlight, but generally wrens are strictly diurnal. Most members of the family roost in cavities or in nests. Multiple nest-building during the breeding season is common among wrens, in some cases, as in the Marsh Wren, to an extraordinary degree, leaving numerous surplus nests for roosting. Some species, however, build nests for specific use as roosting sites. These include many of the Campylorhynchus wrens. Cactus Wrens, for instance, build nests throughout the year, and the juveniles may make tentative efforts at nest-building within days of fledging, with serious construction by ten weeks, obviously long before there is any chance of the youngsters themselves breeding. Wood-wrens, too, construct special roosting nests. In the case of the lowland-dwelling White-breasted Wood-wren, these are quite different from the breeding nest, being of very flimsy construction, and often with little effort at concealment; they are usually placed higher up in forks of slender saplings, so that a predator climbing to the nest cannot avoid shaking the support and alerting the occupant. In contrast, the Grey-breasted Wood-wren, living in the colder highlands, builds a thick-walled, well-insulated and snug roosting nest. White-bellied Wrens (Uropsila leucogastra) also build two types of nest, one a flimsy, thin-walled construction that is presumably intended for roosting only.
Many wrens roost as family groups, or the female sleeps with the young. Juveniles may then roost alone, sometimes, as with the Cactus Wren, in nests not of their own construction. Communal roosting also occurs among Northern Wrens. In this case, the birds forage as individuals during the daytime, gathering together only at dusk, the incentive being mutual body-heat conservation during long, cold nights. Northern Wrens frequently roost in cavities, usually with up to ten individuals together, but up to 96 have been found in one site in Europe and 31 in North America. In roosting aggregations of this kind, the wrens position themselves in layers, and the individuals in each layer hold the head pointing inwards, so that a rough circle is formed.
One extraordinary type of behaviour, found among many wrens of different genera and in totally different habitats, is the destruction of the eggs and, sometimes, the young of other birds, sometimes of conspecifics but very frequently those of other species. Both the Giant Wren of southern Mexico and the Bicoloured Wren (Campylorhynchus griseus) of northern South America have acquired the local dialectal name of “chupahuevo”, meaning literally egg-sucker, apparently owing to a propensity of these wrens to enter chicken coops and attack the eggs therein.
Other troglodytids have developed egg destruction to a much greater degree than an occasional raid on a hen-house. In temperate North America, the Northern House Wren can be extremely destructive of other species. House wrens will enter the nests of other cavity-using species, such as the Carolina Chickadee (Poecile carolinensis), the Tufted Titmouse (Baeolophus bicolor) or the White-breasted Nuthatch (Sitta carolinensis), and either pierce the eggs or throw them out. Not all of the wren’s aggression, however, is directed at cavity-nesters; species such as the Chipping Sparrow (Spizella passerina) may also be victimized, and quail (Odontophoridae) eggs experimentally placed in open nests in Northern House Wren territories may be attacked. The destructive effect of this troglodytid on other avian species has been observed for more than a century, and gave rise to a superbly vitriolic paper by a certain A. Sherman, published in the Wilson Bulletin of 1925, entitled “Down with the House Wren boxes”. Sherman documented in great detail the crimes of the “felonious House Wren”, prophesying that “if no steps are taken to stop his unrestricted breeding it is safe to predict the time will come when all true bird lovers will wring his neck as cheerfully as they now wring the neck of the pestiferous English Sparrow”. Her solution was that persons who put up nestboxes used by these wrens should take them down again, so that “a kind Providence need not protect his memory from the just execrations of future generations”. In one interesting instance observed by Sherman, a Northern House Wren entered a building where there was a preserved shrike (Lanius) nest with blown eggs; the wren pitched the eggs out on to the floor. On being replaced, the eggs were again tossed out by the wren on a second raid, by which time they were a little the worse for wear.
There is circumstantial evidence that nest predation by house wrens may have been heavily implicated in the decline of Bewick’s Wren in eastern North America. In most areas, the appearance of the one coincided with the disappearance of the other. Certainly, the Northern House Wren has a substantial impact on the Prothonotary Warbler (Protonotaria citrea) in Canada, where this cavity-nesting parulid is considered endangered (see Status and Conservation). In southern Ontario, nest predation by the wrens is one of the major causes of nesting failure among the warblers.
Although egg predation by Northern House Wrens has attracted the most attention by virtue of the species’ close association with humans, other, non-cavity-nesting troglodytids, notably the marsh wrens in the genus Cistothorus, are also well known as predators of eggs. In eastern North America, the Marsh Wren frequently attacks the eggs of Red-winged Blackbirds (Agelaius phoeniceus), as well as those of species up to the size of the Least Bittern (Ixobrychus exilis). Intraspecific egg destruction also occurs; females have been seen to kill the chicks of wrens in adjacent territories and to throw them out of the nests. Marsh Wrens can even be caught in traps baited with small eggs. Furthermore, incubating females of the Marsh Wren may show considerable hostility towards their mates, doubtless in order to protect their own eggs; these are unusually thick-shelled, perhaps as a defence against attack. Marsh Wren predation may have a significant negative effect on the breeding success of Red-winged Blackbirds, which, for their part, are very aggressive towards wrens. In western North America, a similar state of mutual hostility exists between Marsh Wrens and Yellow-headed Blackbirds (Xanthocephalus xanthocephalus); the blackbirds may destroy wren nests in order to prevent a brooding female from returning to her eggs. In Colombia, Apolinar’s Wren appears to have an equivalent mutually hostile relationship with the local icterid, the Yellow-hooded Blackbird (Agelaius icterocephalus).
The Sedge Wren in North America exhibits the same behaviour towards marsh-dwelling icterids and may have a significant adverse effect on their populations. Sedge Wrens have been seen to attack the eggs of species as large as the Cinnamon Teal (Anas cyanoptera), but without being able to penetrate the shell. Several other troglodytids, such as the Plain Wren in the genus Thryothorus, have been seen to prey on other species’ eggs or young, and additional observation and fieldwork would doubtless reveal that this behaviour is quite general.
A number of explanations have been advanced for the phenomenon of egg predation by wrens. In some cases the eggs may be wholly or partially eaten, but frequently they are not; eggs are not, therefore, a significant food source. Intraspecific egg destruction may be a useful way of reducing competition for food resources at the period of maximum demand, and it may be relevant that Marsh Wrens, for example, sometimes nest at very high densities with tiny territories. This explanation, however, is less plausible when applied to interspecific predation involving large unrelated species such as the Yellow-headed Blackbird. In the case of the cavity-nesting house wren, the act of destroying the nests of other cavity-nesting species may, in the long run, ensure a supply of nesting sites for the wrens; the latter, being migratory, arrive and commence nesting later than do some resident victims such as the Carolina Chickadee or the Tufted Titmouse. Perhaps significantly, the non-cavity-nesting Northern Wren appears not to prey on eggs. On the other hand, the highly predatory marsh wrens are also non-cavity-nesters.
The behaviour and general habits of the Donacobius resemble those of the mockingbirds more than they do those of the wrens, a fact that, prior to recent DNA investigations, was used by some authors to argue that this species belongs in the family Mimidae (see Systematics). This is a noisy, extrovert bird, usually occurring in small groups of up to four, blood-related individuals. Pairs perform ritualized mutual displays, with much flirting and wagging of the long tail, which is held such that the conspicuous white tips are on show. A more intense form of display involves the adoption of a hunched-back posture, with the head and tail held down, the throat grossly distended, and sometimes with the wings drooped to reveal the conspicuous white flash on the primaries. Both sexes sing. During mutual song sessions, the pair-members may sit close to one another, waving the long tail rhythmically from side to side, with the inflatable yellow throat patch distended. As the Donacobius seems to form long-term pair-bonds, breeds co-operatively and has a rather extended breeding season, it is somewhat difficult, if not impossible, to distinguish between possible breeding displays and general social activity.
For many troglodytids living in arid conditions, water-bathing is not an option. Indeed, even when water is available, the American Rock Wren and the Canyon Wren have not been observed to indulge in this activity, preferring instead to dust-bathe. Cactus Wrens, too, habitually dust-bathe, but they will bathe in water when it is present, even visiting suburban birdbaths for that purpose. Marsh Wrens, but not Sedge Wrens, have been seen to bathe in swamp water. Curiously, water-bathing has not been reported for Northern House Wrens, although both this species and the Carolina Wren do dust-bathe. Bewick’s Wren bathes in both water and dust. There are a few reports of sun-bathing. Carolina Wrens have been seen to lie in the sun with the eyes half-closed, the wings and tail partially spread, and the feathers of the head, back and rump raised.
Most species of wren have been seen to preen, head-scratching being of the indirect type, with the foot lifted over the wing. Allopreening is apparently rare among troglodytids, although it has been observed for a few species.
Aggressive behaviour by wrens is generally associated with territoriality and breeding. Threat displays usually involve the fanning of the wings and the drooping and partial spreading of the tail, while pointing the bill at the object of aggression. Actual physical combat, however, is uncommon. Typically, two individuals will fly vertically upwards for a short distance, while flapping the wings into each other, grasping each other’s feet and sometimes pecking. Occasionally, such efforts are directed against other species. American Rock Wrens, for example, have been seen to attack Northern House Wrens which were attempting to pilfer nesting material from their nest, and have also been observed to attack the much larger Western Kingbird (Tyrannus verticalis).
The Troglodytidae include some of the finest and most appreciated singers among all birds. The Northern Wren, for example, heard throughout the Holarctic Region, is appreciated for the long duration of its song and for the degree of expressiveness contained within its singing. This species’ songs range from barely audible whispered ones, given while courting a female, to songs delivered with a truly surprising vehemence for so tiny a bird. It is the songs of wrens that define certain habitats throughout much of the New World. Examples are the cascading, sweet liq