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Isthmian Wren formerly was known as "Plain Wren", and included with two taxa that now are recognized as separate species, Cabanis's Wren (Cantorchilus modestus) and Canebrake Wren (Cantorchilus zeledoni). "Plain Wren" indeed was a good name of this species, as it possesses rather few obviously distinguishing field marks. This overall similarity is one reason why Cabanis's, Canebrake, and Isthmian wrens were considered conspecific until phylogenetic analyses revealed that each was more distantly related to each other than previously was thought; this genetic divergence also is complemented by differences in their songs. Isthmian Wren has a rather restricted distribution, occurring from southwestern Costa Rica south into Panama. Cabanis's Wren is present on the Pacific coast of northwestern Costa Rica; Cabanis's and Isthmian wrens probably were allopatric, but they may be coming into contact now, in the wake of deforestation in this region. Isthmian Wren builds two different types of nests, a thin-walled, cylinder-like construction that is used by the birds for roosting, and a much more substantial, elliptical structure with a downward-facing entrance, which serves for breeding.
12·5–14 cm. Overall, Isthmian Wren is rather featureless and dull-colored , without strong facial markings or prominent barring or streaking. Adults of both sexes ares similar and have a narrow white supercilium, gray-brown lores and eyestripe; cheeks and ear-coverts mottled dark grayish-brown and gray-white; crown dull gray-brown, back gray-brown, rump pale russet; primaries and secondaries warm brown with obscure darker bars; rectrices dull russet brown with narrow darker bars; throat white, chest pale grayish, center of belly grayish-white, flanks, belly side and undertail-coverts buffy cinnamon (1).
Differs from C. zeledoni in smaller size, much warmer coloration, and is generally duller and paler than C. modestus. Compared with the latter it has a longer bill and shorter tail (2).
maxilla black, mandible grayish
Tarsi and Toes
legs bluish-slate to dull gray
wing 58.6-65 mm (mean 61.4 mm); tail 46-54.5 mm (mean 50 mm); exposed culmen 17-18.5 mm (mean 17.7 mm); tarsus 22-25 mm (mean 23.8 mm); middle toe 13.5-14.5 mm (mean 14.2 mm) (n = 9; 5)
wing 55-58 mm (mean 56.2 mm); tail 44.6-45.5 mm (mean 45 mm); exposed culmen 15.5-16.5 mm (mean 16 mm); tarsus 23-24 mm (mean 23.5 mm); middle toe 13.5-14.5 mm (mean 14 mm) (n = 3; 5)
Frequently, and until recently, treated as conspecific with C. modestus (5, 6, 3, 2), and sometimes also with C. zeledoni (6, 7, 8, 9). A recent study involving mtDNA, morphometrics and colorimetrics has proposed the separation of elutus and modestus into distinct species (10) and, despite some disagreement (11, 2), this treatment has been followed by some authors (12).
Isthmian Wren is found in the southern half of the Pacific Slope of Costa Rica, from the vicinity of San Isidro de El General, San Jose, south and east to just east of the Canal Zone in Panama (7, 13, 4, 10).
Forest edge, second growth, well-vegetated gardens, overgrown citrus plantations with epiphytes, and similar habitats. Mostly in humid forest, but avoids dense wet forest (14, 15, 16, 3). Sea-level to c. 2000 m (13, 8, 9).
None reported, presumably a sedentary resident.
Diet and Foraging
The diet of Isthmian Wren has not been reported in detail, but is presumably similar to that of Cabanis's Wren (T. modestus), and consists largely of arthropods and small invertebrates. Nevertheless, adult seen to feed a berry to fledgling (15). Has been seen to attack eggs of other species, but more probably as a means of reducing competition than for actual food (17). Usually found in pairs, foraging low down in dense vegetation, occasionally higher up in trees (15, 16, 3).
Sounds and Vocal Behavior
Song a loud motif of 3–4 clear whistles, “chin-cheer-gwee” or “chin-cheery-gwee,” sometimes given entirely by male, but frequently as a perfectly timed antiphonal performance, male giving first 2 or 3 notes and female the final one; unmated male has softer, less strident song; recently fledged juvenile sings quite differently, a low diffuse rambling song reminiscent of that of Grey Catbird (Dumetella carolinensis). Calls include harsh “chur” and tinkling “chi-chi-chi” (10, 11, 2)
The nesting of Isthmian Wren is, on the whole surprisingly poorly known. Despite the description of a fair number of nests, little is known of its breeding ecology and behavior, and the nestling period remains poorly defined.
Nest elliptical, the short axis being horizontal, circular entrance hole facing slightly downwards and sometimes protected by short lintel, made from grasses and vegetable fibres, lined with plant down or feathers (19, 15, 18, 3). Dormitory nests are similar to breeding nests, but much more flimsy and usually unlined (19, 15).
Brood Parasitism by Other Species
Disease and Body Parasites
Not evaluated (as separate from T. modestus). Despite small range, is unlikely to be considered globally threatened. Common or abundant in much of its range. Adapts well to modified and regenerating habitat (3, 13, 24).