Bird of the Month: Rock Wren
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
The Rock Wren is a bird of arid, rocky country where its ringing song echoes off rocky cliffs and canyon walls.
A BIRD OF ARID ROCKY HABITAT
The Rock Wren is well-named and well-adapted to its rocky environment. It is found in canyons, on rocky cliffs and boulder fields, along talus slopes, and on the occasional human-constructed retaining wall ranging from British Columbia to Costa Rica. It builds its nest in rocky crevices and lives on a variety of insects including grasshoppers, crickets, leaf-hoppers, and beetles. It has adapted to the dry environment by being able to survive without drinking free water. This was confirmed in an experiment in which five Rock Wrens were kept in captivity with water available for them, but they did not drink (Benedict, et al). It is presumed that the Rock Wren is able to obtain enough moisture from its insect diet.
In general, Rock Wrens are easily seen as they often perch on top of rocks, but they can sometimes sing from hidden places (Bell and Kennedy). The song is a ringing series of repeated phrases which peal across long distances. The song can be heard and their unique “bobbing” behavior, which looks like quick deep knee bends, can be seen on video at the Macaulay Library.
Rock Wren
Scientific Name: Salpinctes obsoletus
Length: 6”
Wingspan: 9”
Weight: 0.58 oz (16.5g)
AOU Alpha Code: ROWR
NEST PAVED WITH STONES
Rock Wrens begin their nest construction by laying a walkway or trail of small, flat stones or pebbles which lead to the nest site. Speculation about the purpose of the walkway includes suspicion that by raising the surrounding area the opening to the nest site is made smaller as a protection against predators. The raised area may also help keep the nest area dry, or it may be decoration. The stones comprising the walkway can number into the hundreds (Benedict, et al).
The nest site is at the end of the walkway in a crevice among rocks, under a rock ledge, and sometimes in a hole in a dirt bank. The cup nest is built from grass, weeds, and small twigs and lined with animal hair, spider webs, and feathers. Usually, 5-6 white eggs dotted with reddish-brown are deposited. Details of incubation and time to fledging are not known due to limited study of these hard-to-reach nests.
STATUS AND DISTRIBUTION
Rock Wrens are common, year-round residents within much of their range which extends from southern British Columbia through the Pacific Northwest east of the Cascades and through the western United States and central Mexico. The breeding range has been expanding northward to part of central British Columbia over the past century (Aversa, et al). Some individuals that breed in north-central Washington withdraw to the south of Washington in winter.
The Rock Wren is the sole member of the genus Salpinctes, which is from the Greek, salpigktes, for a trumpeter. The name is a reference to the Rock Wren’s ringing song. The species epithet obsoletus is Latin for shabby and dingy with reference to the bird’s dull grayish-brown plumage (Holloway). The Rock Wren is sympatric with the Canyon Wren (Catherpes mexicanus) as both breed in canyons and on cliffs. Distinguishing the two species in the field is clear by their different songs, and also by the Rock Wren’s overall gray and pale buffy coloration when compared to the bright white throat and upper chest and rufous belly of the Canyon Wren.
CONSERVATION
The Rock Wren is rated by Bird Life International as a species of Least Concern. This wren spends most of its life away from humans at higher elevations and around rocky outcroppings and is little disturbed by human activity. There are no conservation measures in place. However, there is a need for further research as little is known with certainty about the bird’s population. There are trend data that suggest the Rock Wren has expanded its range into southern British Columbia and the Great Plains. On the other hand, some data reflect an overall increase in the North American population from the 1970s to the 1990s and a gradual decline since then. The current world population in North America, Mexico, and Central America is estimated at 4,100,000 individuals.
Photo credit by Mick Thompson. References available upon request from amccormick@eastsideaudubon.org.