Although many participants in The Birdhouse Network (TBN) report seeing House Wrens (Troglodytes aedon) or occasionally Carolina Wrens (Thryothorus ludovicianus) using their nest boxes, few are even aware of a third cavity-nesting wren in North America. And

Photo credit: Stan Pavlov/Cornell Lab of Ornithology

The Bewick’s Wren has whiter underparts than the similar Carolina Wren and is smaller and more slender. The broad white eyebrow of the Bewick’s Wren sets it apart from the smaller House Wren. It also has a distinctive way of twitching its tail from side to side. Western forms are grayer than the brownish eastern races, and they sing a simpler song than the complex eastern versions, which are distin-guishable from the rolling song of the Carolina Wren.

yet, the Bewick's Wren (Thryomanes bewickii) may be the one most in need of help from citizen scientists, given the recent population trends of the species in the East. Bewick's Wrens readily take to nest boxes and are still relatively common in many western states, but they occur in our database only 41 times in the past three years, with reports from four states: Texas, Oklahoma, California, and Oregon. We hope to use data collected by TBN members to help reverse this wren's decline.

Although records indicate Bewick's Wrens were once fairly common in many eastern states, the species is now found almost exclusively west of the Mississippi River. The range of the Bewick's Wren has fluctuated ever since John James Audubon described the species in 1821. Historically, the range expanded with the establishment of farmlands and pastures in southern Iowa and Minnesota, New York, and the western portions of the Mid-Atlantic States. By the 1930s Bewick's Wrens were considered "fairly common" to "common" breeders throughout the Appalachians and Mid-west. The trend has since reversed, however, and most of the eastern populations had essentially disappeared by the 1980s. Over the next 20 years, the populations that did remain in the East declined more than 8 percent per year, according to the Breeding Bird Survey. The Bewick's Wren is now listed as endangered, threatened, or of special concern in many of the Midwestern and all of the eastern states where it occurs.

The Bewick’s Wren is widespread, but populations are discontinuous. The migratory eastern birds are rare and local breeders. The resident midwestern and western birds expand their ranges slightly northward in the breeding season. The highest year-round concentrations occur in central Texas, southeastern Arizona, and coastal southern California. (Map adapted from Kennedy, E. D. and D. W. White. 1997. Bewick’s Wren (Thryomanes bewickii). In The Birds of North America, No. 315 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, Penn., and The American Ornithologists’ Union, Washington, D. C.)

This dramatic decline cannot be attributed to a single cause. Instead researchers suspect multiple factors, including an increase in the use of pesticides, loss of suitable breeding habitat, an unfortunate string of severe winters, and competition with other birds, most notably the House Wren. Overlap of the wrens' breeding habitats and nest sites is common, and House Wrens have been shown to displace Bewick's Wrens to adjacent, possibly less-optimal, habitats. One study found that egg removal and nest destruction by House Wrens caused 81 percent of the nesting failures of Bewick's Wrens. Perhaps not coincidentally, as the House Wren's breeding range expanded, the Bewick's Wren's shrank.

Primarily found in brushy areas or thickets, the Bewick's Wren often forages energetically for beetles, wasps, caterpillars, spiders, and other insects, rarely staying still for more than a few seconds. During the breeding season, the male sings a variable song reminiscent of a Song Sparrow's. In the West, where Bewick's Wrens are resident over much of their range, nesting may get underway by late February, with early breeders more likely to raise young successfully.

For nest sites, Bewick's Wrens use natural or artificial cavities, open crags, and stumps. They may even nest in a shed, garage, or barn. Like the House Wren, the male initiates nest building by constructing a foundation that may include sticks, twigs, rootlets, moss, leaves, or feathers. Unlike the House Wren, the Bewick's Wren does not completely fill the cavity with sticks, and it constructs only one nest instead of multiple "dummy nests." The male and female Bewick's Wrens share nest-building duties.

Bewick's Wrens usually raise a single brood, though second broods are possible. The female lays between three and eight eggs. If the clutch fails, she lays a replacement clutch in a new nest. The eggs, paler and more finely speckled than those of the House Wren, hatch after 14 to 16 days. Both parents feed the nestlings.

During the Bewick's Wren's eastern expansion during the 1800s, human habitation initially created favorable habitat-mixtures of thick scrubby vegetation near open woodlands. Vegetative succession in abandoned agricultural fields may now be limiting these habitats. To attract Bewick's Wrens in eastern and midwestern habitats, provide nest boxes in natural or disturbed areas that feature a dense, brushy understory and an open overstory. In the West, Bewick's Wrens are commonly found in scrubby chaparral, piñon-juniper shrublands.

Another way to help Bewick's Wrens, paradoxically, may be to remove nest boxes-but only in areas with high concentrations of House Wrens, which displace Bewick's Wrens from favorable nesting sites. It's best to remove nest boxes during the non-breeding season or only when you are sure they have no current occupants. Please also remember that it is a violation of federal law to harm or harass any native species such as the House Wren, including removing

nesting material and eggs from a nest site. We hope TBN participants will focus on monitoring the progress of the Bewick's Wren, a species that readily takes to nest boxes, even those placed close to human dwellings.

You should set up nest boxes as early as February to accommodate the wrens' early nesting habits. Report your results to The Birdhouse Network. And if you hear of Bewick's Wren sightings in your area, encourage others to establish and monitor a nestbox!

Have you seen Bewick’s Wrens east of the Mississippi River, especially in the Appalachian region where the species is feared to be extinct? The Birdhouse Network needs your data! For more information go to http://birds.cornell.edu/birdhouse