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Rock Wren Life History

Habitat

Habitat DesertsRock Wrens inhabit dry, rocky habitats that are sparsely vegetated, from deserts below sea level to alpine mountaintops in Colorado that top 12,000 feet. Rock Wrens breed in high-latitude and high-altitude portions of their range (southwestern Canada and the Rocky Mountains, respectively) but wintering birds also use dry, rocky habitats. In Canada, Rock Wrens favor rocky shrubsteppe with sagebrush, rock outcroppings, cliffs (often within grasslands or pine forest), canyon walls, and talus slopes. They occupy similar settings in the Rockies and the Pacific Northwest, where clearcuts, ravines, and steep valleys also provide habitat. In addition to the habitats above, Rock Wrens in California inhabit ocean bluffs, breakwaters, rocky coastal reefs, alpine meadows, dry gravelly washes and arroyos, and desert mesas. Migrants can often be found in agricultural settings and grasslands, often in distressed parts of the landscape—piles of construction debris, stone quarries, rock piles, and abandoned surface mines.Back to top

Food

Food InsectsRock Wrens feed mostly on ground-dwelling insects, among them ants, grasshoppers, crickets, leafhoppers, bugs, beetles, as well as spiders, seeds, and other plant matter. Although they inhabit dry areas, they sometimes eat aquatic insects such as dragonfly nymphs and whirligig beetles. They sometimes pirate food from spiderwebs. Rock Wrens forage in open environments, usually hunting on the ground and using the bill to probe into crevices as they hop or creep along. They often make short leaps to catch insects but rarely pursue insects in extended flights. During the heat of the day, they rest or forage in shaded areas. They may enter woodrat middens to search for food. No observation of a Rock Wren drinking water has been reported, and it seems this species takes the moisture it needs from its prey. Back to top

Nesting

Nest Placement

Nest GroundBoth sexes search for a suitable site. The nest is normally set on a stone floor, in a cavity within or between rocks.

Nest Description

Both male and female build the nest, a loose cup of grass, bark, moss, and hair, lined with rootlets, hair, wool, and spider silk. Males typically gather more material, which is placed by the female. The nest is built upon a foundation of tiny stones (and sometimes sticks), and this foundation sometimes extends into a stone “walkway” out of the crevice and into the open, where it may help conceal the nest crevice. Nest measurements average 3.5 inches across, 1.3 inches deep, with interior cup 2.6 inches across and 1.1 inches deep.

Nesting Facts

Clutch Size:4-8 eggs
Number of Broods:2-3 broods
Egg Length:0.6-0.8 in (1.58-2.03 cm)
Egg Width:0.5-0.6 in (1.37-1.57 cm)
Incubation Period:14-16 days
Nestling Period:14-16 days
Egg Description:White with fine spots of reddish brown.
Condition at Hatching:Helpless, with some down.
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Behavior

Behavior Ground ForagerRock Wrens are socially monogamous. Courtship behavior appears to be limited to males bringing food to females. Males are territorial and also guard females, particularly before egg-laying. Territory size varies depending on habitat; one study found that territories covered about 4.5 acres. Males often perch on promontories that look out over the territory. They drive out other Rock Wrens by calling and threat displays, usually a steady bobbing of the body. If that fails, they fly directly at the rival, clashing in the air or the ground and beating the opponent with bill and wings. They also chase away House Wrens, which destroy Rock Wrens’ (and many other passerines’) eggs. In turn, Rock Wrens may be evicted from the vicinity of Canyon and Cactus Wren nests, but in many areas, these species appear to coexist without conflict. Both sexes feed and care for young. Rock Wrens are solitary in winter and apparently not territorial but are usually well spaced in winter habitat. Back to top

Conservation

Conservation Low Concern

Throughout its range, Rock Wren numbers declined by an estimated 0.65% per year between 1968 and 2015, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 4.1 million and rates the species an 11 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. The reasons for the sharp decline in this species’ population are unclear. Some have become trapped in PVC posts used to mark mine claims (a pervasive problem for many bird species in the open range of the Intermountain West); in several areas, brood parasitism by Brown-headed Cowbirds has reduced nesting success. Rock Wrens appear to be able to tolerate modifications or disturbances to habitat.

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Credits

Lowther, P. E., D. E. Kroodsma, and G. H. Farley. 2000. Rock Wren (Salpinctes obsoletus). In The Birds of North America, No. 486 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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