| Rock wren | |
|---|---|
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Troglodytidae |
| Genus: | Salpinctes Cabanis, 1847 |
| Species: | S. obsoletus |
| Binomial name | |
| Salpinctes obsoletus (Say, 1822) | |
| Subspecies[2] | |
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Breeding Migration Year-round Nonbreeding | |
| Synonyms[3] | |
Therock wren (Salpinctes obsoletus) is a smallsongbird of thewren family native to the rocky areas of westernNorth America. There are 8 subspecies of the rock wren, one of which is extinct. They are similar in size to other wrens, with a grey-brown coat, a brown rump, and a speckled white throat. They are visually similar to thecanyon wren, which they share a habitat with. They are noted for their variablesong and song pattern, used forterritory defense, as well as their habit of building "pavements" with flat rocks around their nest to help nestlings stay dry. Rock wrens areserially monogamous, forming pairs for nesting season. Nestbuilding usually begins in March, usually in crevices, and the first brood are laid late April to June, with a possible second brood later in June. They are largely terrestrial foragers, rarely flying. Their diet consists ofinsects, mostlyweevils, during the spring and summer, shifting tograin during autumn and winter. Though they are aleast-concern species, their population size has declined by 13% from 2010 to 2020.
The rock wren was first described byThomas Say, published inEdwin James' bookAccount of an Expedition from Pittsburgh to the Rocky Mountains, asTroglodytes obsoleta.[4] The work was available in 1822, even though the date printed on the title page is 1823; 1822 thus counts as the date of description of the species.[5] It was later moved to its own monotypic genus,Salpinctes, byJean Cabanis in 1847, because of its straighter tail.[6]Salpinctes formerly included thecanyon wren (synonymThryothorus mexicanus), but it was later removed.[6]
The genus name,Salpinctes, comes from theGreek word for 'trumpeter'. Its specific epithet,obsoletus, is Latin for 'worn out'. There are 8 subspecies, split into 2 groups (obsoletus andguttatus).[2]
The rock wren is between 12.5–15 cm (4.9–5.9 in) in length and has awingspan of 22–24 cm (8.7–9.4 in). It has a bill length of 18.7 mm (0.74 in) in males and 17.8 mm (0.70 in) and females. Its wing length is 70.3 mm (2.77 in) in males, and slightly less at 67.8 mm (2.67 in) in females; similarly, its tail length is 51.9 mm (2.04 in) and 47.8 mm (1.88 in) in males and females, respectively. However, males weigh 15.7 g (0.55 oz), slightly less than females, who weigh 17.2 g (0.61 oz).[2][7]
Rock wrens have grey-brown upperparts with small black and white spots and pale grey underparts with a light brown rump.[8] Additional features include a light grey line extending through the eye, a long and sharpbill,[9] a speckled light gray throat, a long barred tail, zebra-striped undertail coverts, and dark legs.[2] The juvenile plumage is similar to that of an adult, except for a slightly more vibrant buff, similar to a washed-out cinnamon color, fluffier body feathers, and the absence of a dark streak and spots on the underparts.[2]
Though they are very distinct in their habitat, it is possible to confuse them with thecanyon wren, which have superficially similar coloring; however, the canyon wren has solid white throats and generally brighter, less muddled colors.[2][10]
Rock wrens are permanent residents in the south of their range, includingCalifornia; westernWashington; northernNevada,Arizona, andNew Mexico; southernGuatemala andNicaragua; northwesternCosta Rica andPanama; and inlandMexico, includingBaja California.[2][11] They are also residents ofGuadalupeIsland andSan Benito Island.[2] They are occasional vagrants in the eastern United States. During the breeding season, their range extends to the southern interior ofBritish Columbia, as well asWyoming,Montana,Idaho, andUtah.[9] They are commonly found in rocky open habitats, such as exposed rock, canyons, cliffs; however, rock is not a firm requirement, as they can also be found in large eroded sandbanks.[2] Rock wrens are rare in urban areas, instead preferring rocky areas with at least some steep features, enough shrubbery to forage in, and ample crevices for nesting.[2] The rock wren is very tolerant of altitudes, breeding from 60 m (200 ft) to 3,600 m (11,800 ft) above sea level;[12][13] however, they are most common below 2,000 m (6,600 ft).[2]
Rock wrens areserially monogamous. During nesting season, males are territorial, guarding their area of around 1.8 hectares (4.4 acres) in size with songs, calls, and threat displays, such as bobbing. Males have been observedcourting by bringing food to females.[2]
Nest-building begins in March, and the first brood occurs late April to June, and a second brood can occur from mid-June to early August, with up to 3 broods per year. Rock wrens nest on stone surfaces in crevices, cavities, or other similar sheltered areas. They lay 5–6eggs perclutch, withincubation being around 14–16 days.[8] Incubation is handled by the female alone; however, males will occasionally bring food.[2]
Eggs are ovate, usually 18.6 mm × 14.8 mm (0.73 in × 0.58 in) in size and around 2.27 g (0.080 oz) in mass.[14] One egg is laid per day.[2]
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The outsides of the nests are roughly 8.9 cm (3.5 in) in diameter and 3.4 cm (1.3 in) in depth, with the inside 6.7 cm (2.6 in) and 2.9 cm (1.1 in) in diameter and depth, respectively.[15] Nests are usually built in cavities with openings around 2 times the bird's height, or 10.2 cm (4.0 in).[2] They are built on top of a stone foundation, and consist of stones, plant material, trash, and other debris.[16] Nests often include a "pavement" made with stones leading up to the nest to keep the nest and nestlings dry, helping them maintain their body temperature.[17] Pavements consist of flat stones, on average 3.1 g (0.11 oz) in weight, 27 by 18 mm (1.06 by 0.71 in) in width and length, and 5 mm (0.20 in) thick. These stones weigh on average 20% of the bird's body mass, with an average of 230 stones per nest; the amount of stones vary with the size of the nest cavity, with larger cavities having more stones.[18]
Nestlings leave the nest around 14–16 days old, moving to a different rock within 75 m (246 ft) from the nest, continuing to receive care from parents for about 1 week, and remained on the parent's territory for 4 more weeks. Nestlings molted at 28–35 days, however, they still possessedgape flanges.[2]
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Rock wrens are largely terrestrial, only flying for short durations, and instead using a very rapid gait to move around.[10][2] They eatinsects, such asleafhoppers,ants, andweevils; occasionally, other arthropods likespiders; and, rarely,seeds.[10][2] Rock wrens mainly forage during the day on open ground, rummaging the surface of rocks and soil and probing crevices.[2]
Nestlings were observed being fed grasshoppers, along with other insects; however, large portions of the prey could not be identified due to their small size.[19]
| Songs and calls |
Female rock wrens do not sing; however, males have large repertoires of 69–119 syllables, each song a 1–2.5 second trill of repeated syllables, with 3–5 seconds between songs.[8][2] Rock wrens have five call types: a two-parttic-ear/spit-tee sometimes used to warn of intruders; a rough trill, sometimes following aspit, used as an alarm; an agitated chatter; and an aggressivek'chee used during confrontations.[2]
Rock wrens sing with a distinctive pattern intermediate between "eventual variety" (repeating one syllable before switching) and "immediate variety" (never repeating). A male typically sings each syllable three to four times within a burst of 10–15 syllables, rarely repeating the same syllable consecutively.[20] Song is primarily used for territorial defense, with males having greater repertoire size and pitch variety being more effective at deterring rivals.[19][2]
The rock wren is aleast-concern species on theIUCN Red List, with an estimated population of 3.4 million in the United States and Canada, with the global population being around 4.1 million.[21][2] However, the population is slowly declining, with a 13% decrease in population from 2010 to 2020.[22] The cause of this is unknown.[8] Little is known about the causes of mortality or lifespan in adults,[2] but nests are subject to predation.[2] Observed nest predators included thestriped racer snake, thedesert woodrat, and thewhite-tailed antelope squirrel,[2] as well asbullsnakes andprairie rattlesnakes.[23]Brown-headed cowbirds are brood parasites of this species.[2]
Genus Troglodytes, Cuvier — T.obsoleta, Say. Above dusky-brownish, slightly undulated with pale, tinted with dull ferruginous on the top of the head and superior portion of the back; sides of the head dull whitish, with a broad brown line passing through the eye to the origin of the neck; primaries plain, being entirely destitute of undulations or spots; tail coverts pale, each with four or five fuscous bands; chin, neck beneath, and breast whitish, each feather marked by a longitudinal line of light brown; belly white; flanks a little tinged with ferruginous; inferior tail coverts white, each feather bifasciate with black-brown; tail simple, broadly tipped with ferruginous-yellow, and with black before the tip, the remaining portion color of the wings, and obsoletely banded; these bands are more distinct on the two middle feathers, which are destitute of the black and yellowish termination; exterior plume marked by four yellowish white spots on the exterior web, and by two larger ones on the inner web; the tip is dusky, length six inches; bill, from the corner of the mouth, rather more than one inch.
Strongly migratory, departing from northern part of range for the winter. Strays sometimes wander east in fall, and have even reached the Atlantic Coast.
