Rock Wren

The rock wren is between 12.5–15 cm (4.9–5.9 in) in length and has a wingspan 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) in 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). Rock wrens have grey-brown upperparts with small black and white spots and pale grey underparts with a light brown rump. Additional features include a light grey line extending through the eye, a long and sharp bill, a speckled light gray throat, a long barred tail, zebra-striped undertail coverts, and dark legs. 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. Though they are very distinct in their habitat, it is possible to confuse them with the canyon wren, which have superficially similar coloring; however, the canyon wren has solid white throats and generally brighter, less muddled colors.

Rock wrens are permanent residents in the south of their range, including California; western Washington; northern Nevada, Arizona, and New Mexico; southern Guatemala and Nicaragua; northwestern Costa Rica and Panama; and inland Mexico, including Baja California. They are also residents of Guadalupe Island and San Benito Island. They are occasional vagrants in the eastern United States. During the breeding season, their range extends to the southern interior of British Columbia, as well as Wyoming, Montana, Idaho, and Utah. 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. 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. The rock wren is very tolerant of altitudes, breeding from 60 m (200 ft) to 3,600 m (11,800 ft) above sea level; however, they are most common below 2,000 m (6,600 ft).

Rock wrens are serially 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 observed courting by bringing food to females.

Breeding. 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 5–6 eggs per clutch, with incubation being around 14–16 days. Incubation is handled by the female alone; however, males will occasionally bring food. 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. One egg is laid per day.

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. Nests are usually built in cavities with openings around 2 times the bird's height, or 10.2 cm (4.0 in). They are built on top of a stone foundation, and consist of stones, plant material, trash, and other debris. 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. …