Family Wrens (Troglodytidae)

Least Concern

Pacific Wren (Troglodytes pacificus)

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Taxonomy

French: Troglodyte de Baird German: Pazifikzaunkönig Spanish: Chochín del Pacífico
Taxonomy:

Troglodytes hyemalis [sic] (var. pacificus

) S. F. Baird

, 1864,

Simiahmoo, Puget Sound, Washington

.

Until recently considered conspecific with T. troglodytes and T. hiemalis, given great morphological consistency, but acoustic and genetic analyses suggest otherwise, and present species proves to be very narrowly sympatric with T. hiemalis#R, so review of characters not strictly necessary; but differs from latter in its much greater number of repeated series of notes in song (3)#R; higher-pitched and shorter call note (seemingly “tsip” vs “chup”) (2); (on published evidence#R) slightly longer tail (allow 1) and shorter wing (allow 1); and usually buffier supercilium and spots on closed primaries#R (ns). Differences from T. troglodytes, whose most easterly outpost is Commander Is 400 km W of Attu, the westernmost outpost of present species, not yet determined other than in voice, with larger number of repeat series in song (2) and higher average pace of repeats in song (2), although in general it also shows a plainer (less mottled) breast and upper flanks (ns); research needed to confirm degree of difference between these taxa, especially where they approach each other in Bering Sea. Other proposed races include tanagensis, seguamensis, petrophilus and stevensoni, all included within kiskensis; and ochroleucus, muiri and obscurior, merged into pacificus. Seven subspecies recognized.

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Subspecies and Distribution
  • T. p. alascensis S. F. Baird, 1869 – Pribilof Is (St George, St Paul, Otter).
  • T. p. meligerus (Oberholser, 1900) – W Aleutian Is (Attu, Buldir).
  • T. p. kiskensis (Oberholser, 1919) – Aleutians (from Kiska E to Unalaska) and W Alaska Peninsula (including Amak I and Amagat I).
  • T. p. semidiensis (W. P. Brooks, 1915) – Semidi Is, off S Alaska Peninsula.
  • T. p. helleri (Osgood, 1901) – Kodiak I and Afognak I, off S Alaska.
  • T. p. pacificus S. F. Baird, 1864 – W North America from SE Alaska (including the islands of Baranoff, Admiralty, Chichagof, Mitkof and Kupreanof), SW Yukon and coastal British Columbia S to S California.
  • T. p. salebrosus Burleigh, 1959 – interior British Columbia and SW Alberta S to NE Oregon and W Montana; non-breeding S to Arizona and S California.
  • Descriptive notes

    9–11 cm; 8–12 g. Small, dark wren with short tail, small bill and pale supercilium, chin and throat. Upperwing-coverts rufous-brown with darker barring; primaries and secondaries brown, barred darker; upper breast light wood brown#R; belly and flanks more richly coloured than breast, with dark barring; rectrices chestnut-brown with dusky bars; irides brown; bill pale brownish, lighter at base; legs and feet light brown. Very similar to formerly conspecific T. hiemalis, but darker overall and more richly coloured with more rufous tones, especially on throat and breast; sympatric T. aedon is larger, with longer tail and less prominent barring on belly. Sexes similar. Juvenile resembles adult, but brown of back, scapulars, rump, and uppertail-coverts is unmarked, superciliary and postocular stripes are indistinct and underparts darker, with feathers distinctly fringed dusky; barring on flanks, vent and undertail-coverts less distinct#R. Races differ in size and in coloration and pattern of plumage#R: alascensis fairly large, medium brown on throat and breast, with browner flanks; meligerus is large, with dull dark, dusky-brown upperparts; kiskensis is similar to previous, but lighter and less rufescent above; semidiensis is palest of Alaskan subspecies, with greyer upperparts; helleri similar to nominate but without rufescent tones, upperparts uniformly dark brown; pacificus has short bill, dull rufous-brown throat and breast, dark rufous-brown upperparts; salebrosus is like nominate but with browner (versus rufescent) upperparts and paler, browner throat and breast.

    ssp alascensis  

    Drawing by Hilary Burn
    ssp alascensis  
    Descriptive notes:

    9–11 cm; 8–12 g. Small, dark wren with short tail, small bill and pale supercilium, chin and throat. Upperwing-coverts rufous-brown with darker barring; primaries and secondaries brown, barred darker; upper breast light wood brown#R; belly and flanks more richly coloured than breast, with dark barring; rectrices chestnut-brown with dusky bars; irides brown; bill pale brownish, lighter at base; legs and feet light brown. Very similar to formerly conspecific T. hiemalis, but darker overall and more richly coloured with more rufous tones, especially on throat and breast; sympatric T. aedon is larger, with longer tail and less prominent barring on belly. Sexes similar. Juvenile resembles adult, but brown of back, scapulars, rump, and uppertail-coverts is unmarked, superciliary and postocular stripes are indistinct and underparts darker, with feathers distinctly fringed dusky; barring on flanks, vent and undertail-coverts less distinct#R. Races differ in size and in coloration and pattern of plumage#R: alascensis fairly large, medium brown on throat and breast, with browner flanks; meligerus is large, with dull dark, dusky-brown upperparts; kiskensis is similar to previous, but lighter and less rufescent above; semidiensis is palest of Alaskan subspecies, with greyer upperparts; helleri similar to nominate but without rufescent tones, upperparts uniformly dark brown; pacificus has short bill, dull rufous-brown throat and breast, dark rufous-brown upperparts; salebrosus is like nominate but with browner (versus rufescent) upperparts and paler, browner throat and breast.

    ssp pacificus  

    Drawing by Hilary Burn
    ssp pacificus  
    Descriptive notes:

    9–11 cm; 8–12 g. Small, dark wren with short tail, small bill and pale supercilium, chin and throat. Upperwing-coverts rufous-brown with darker barring; primaries and secondaries brown, barred darker; upper breast light wood brown#R; belly and flanks more richly coloured than breast, with dark barring; rectrices chestnut-brown with dusky bars; irides brown; bill pale brownish, lighter at base; legs and feet light brown. Very similar to formerly conspecific T. hiemalis, but darker overall and more richly coloured with more rufous tones, especially on throat and breast; sympatric T. aedon is larger, with longer tail and less prominent barring on belly. Sexes similar. Juvenile resembles adult, but brown of back, scapulars, rump, and uppertail-coverts is unmarked, superciliary and postocular stripes are indistinct and underparts darker, with feathers distinctly fringed dusky; barring on flanks, vent and undertail-coverts less distinct#R. Races differ in size and in coloration and pattern of plumage#R: alascensis fairly large, medium brown on throat and breast, with browner flanks; meligerus is large, with dull dark, dusky-brown upperparts; kiskensis is similar to previous, but lighter and less rufescent above; semidiensis is palest of Alaskan subspecies, with greyer upperparts; helleri similar to nominate but without rufescent tones, upperparts uniformly dark brown; pacificus has short bill, dull rufous-brown throat and breast, dark rufous-brown upperparts; salebrosus is like nominate but with browner (versus rufescent) upperparts and paler, browner throat and breast.

    Voice

    Male’s song remarkably long and complex, a series of tumbling, tinkling trills that lasts for 5–10 seconds (mean c. 6 seconds#R#R); female not known to sing. Relative to song of T. hiemalis, quality more harsh and staccato, and rate of frequency modulation and overall mean frequency are higher#R#R. Also gives sharp “timp” and “chek chek” calls#R. Individual males recorded over two mornings produced an average of 21 song types (range = 8–47), and their songs comprised 137–385 syllables (mean = 261)#R. Singing males cock their tails forward and swing their heads from side to side; during agonistic encounters, song is stifled, harsh and usually accompanied by rapid wing-flipping#R. Ambient noise can influence singing behaviour; in British Columbia, Canada, wrens with territories near highway traffic increased song length, and those with territories near ocean surf produced songs with longer syllables and exhibited higher intra-individual variation in song duration#R.

    Habitat

    Breeds in boreal moist coniferous forest with extensive understorey, deciduous forest and mixed deciduous/coniferous forest; also on islands with stunted vegetation and no large trees in Aleutians#R. Often frequents mature and old-growth forest#R#R, and sometimes associated with wetlands (bogs, swamps, streams, lakes), but also occurs in forest far from water. In British Columbia, abundance higher along river stretches with spawning salmon (Oncorhynchus spp.) than along those without salmon, probably because presence of salmon increased the abundance of invertebrate prey#R. From sea-level to 3720 m in Sierra Nevada range. Uses wider range of habitats in winter, including more open woodland, deciduous riparian forest, logged areas with slash piles, and parks and gardens if brush piles and dense tangles of vegetation are available.

    Food and feeding

    Bulk of food invertebrates such as insects (especially Coleoptera, Hemiptera, Diptera, Lepidoptera, Hymenoptera), spiders, amphipods and centipedes; also reported to consume snails and fruits#R. Forages on ground, on decaying logs and root masses of fallen trees, in understorey vegetation, around trunks of standing trees, and cliff crevices. Of 122 stomachs examined from birds taken in British Columbia throughout year, 66% contained beetles, 51% spiders, 30% moth and butterfly larvae, 23% mites and ticks, 22% bees, wasps and ants,14% flies, 11% pseudoscorpions, 10% millipedes and 10% harvestmen#R.

    Breeding

    Egg-laying begins early to mid Apr in Oregon, mid Apr in British Columbia, late Apr in Idaho, late May in Alaska#R and may continue into mid to late Jul; two or sometimes three broods attempted per season. At two study sites in Alaska with low nest predation (2% of 65 nests depredated), 22% and 78% of males were polygynous, whereas at a third site with higher nest predation (19% of 59 nests), only 10% of males were polygynous#R. Nest typically domed, with side entrance hole, made of grass, moss, twigs, bark, rootlets, shreds of rotten wood, feathers and hair, and placed in a wide variety of substrates including old woodpecker cavities, natural cavities, in rootwads of fallen trees, in creek banks and decaying logs, in moss clumps on trees, and within upright trees, and at ground level to as high as 18 m above ground#R#R. Male does most of building and often constructs surplus nests, while female selects nest to be used and adds lining. Predation by red squirrels (Tamiasciurus hudsonicus) thought to result in higher nest heights in Alaska#R. Clutch size 3–9 eggs, typically 5–7, larger clutches (up to 12 eggs) probably result of two females laying in same nest, island races tend to lay smaller clutches; eggs clear white, spotted pale brown or reddish brown, especially at blunt end, more rarely almost immaculate, race meligerus (W Aleutian Is) pure unspotted white; size 14–19·2 mm × 11·6–14 mm, tending to be larger in Alaska#R; incubation by female alone, period c. 16 days; young fed by both parents, brooded by female alone, nestling period 14–19 days, mean c. 17 days; fledgling care continues for 9–18 days more before young become independent. Estimates of nesting success (proportion of nests raising at least one fledgling) c. 30–90%#R#R#R. Across an elevational gradient of 100–1300 m in SW British Columbia, adult philopatry, nest survival and nestling mass declined with elevation, suggesting that in some areas, at least, the species is poorly adapted to breed at higher elevations#R. Longevity record a female that was at least 6·5 years old when caught and released during ringing operation in California.

    Movements

    Resident, migratory and partially migratory; movements nocturnal. Present year-round along Pacific Coast from Aleutian Is to C California and in interior to SW Alberta and W Montana. Remaining parts of breeding range mostly evacuated in winter, including higher elevations in mountains. Even where present in winter, however, e.g. W Montana, numbers seemingly much reduced from those in summer. Spring migrants leave wintering grounds between mid Mar and late Apr and arrive on breeding grounds from late Mar to late May; autumn migrants head S from late Jul to early Nov and arrive on wintering grounds between Sept and Dec#R#R. Has wandered to New Mexico.

    Status and conservation

    Not globally threatened (Least Concern). Considered common over much of range, but no data on overall numbers. Breeding Bird Survey data indicate a well-supported decline in numbers of 1·1% per annum in the Northern Pacific Rainforest region in the period 1966–2015#R. Hard winters with prolonged snow cover can cause severe declines in numbers in non-migratory populations, although such declines typically are temporary. In the Haida Gwaii archipelago, British Columbia, wrens were less abundant on islands with a long history of browsing by deer than on deer-free islands#R. Greatest threat to species is clear-cut logging of mature and old-growth coniferous forest, which can result in decreased numbers of breeders owing to loss of critical habitat components such as downed logs, snags and large standing trees#R. Leaving snags, slash piles and rootwads from downed logs after timber harvest could help mitigate negative effects of logging.

    Recommended citation

    del Hoyo, J., Collar, N. & Marks, J.S. (2018). Pacific Wren (Troglodytes pacificus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/1343991 on 21 October 2018).