A Wren for All Seasons

Walking past the sage-scrub open space in the pre-dawn winter twilight, I heard a number of birds singing loudly.  Some sounded like Song Sparrows improvising a different intro and jazzier closing notes—maybe a different song for winter than summer?  Others made me think of extremely musical Spotted Towhees, although Spotteds (and most songbirds) don’t sing in the winter. I’d heard this winter twilight chorus each morning lately.  What on earth was going on here? Nathan Pieplow’s Peterson Field Guide to Bird Sounds of Western North America held the secret.  “Sings nearly all year; extremely varied songs.  Long versions can be confused with Song Sparrow; short versions, with … Spotted Towhee.”  Mystery solved. My multitude of pre-dawn winter singers were all Bewick’s Wrens!

A medium-sized wren (at least as wrens go) with a conspicuous white line over the eye (a supercilium) and a relatively long tail tipped with white spots, a Bewick’s Wren characteristically wags that tail from side to side. The sheer uniformity of the plain grayish brown plumage makes the long, narrow supercilium pop.

Even though he’s a mere featherweight, the feisty Bewick’s Wren nonetheless belts out his song in any season, berating any and all intruders on his territory like a pugnacious bouncer.  The bird often scolds without prompting; just your presence suffices to elicit a stream of harsh chatter. No matter what’s going on, the nimble and acrobatic Bewick’s Wren never stays still for long.

Pretty much a permanent resident along the West Coast, the Bewick’s Wren is one of San Diego County’s most widespread birds. These wrens choose a variety of habitats including chaparral, brushy thickets, riparian woodlands, sage scrub, and well-vegetated suburban areas.  In the breeding season they inhabit most of the coastal slope, ranging to the highest point in the county (Hot Springs Mountain, 6526’). The species’ abundance on the coastal slope follows no obvious pattern, although not many occur in extensively developed or heavily forested areas. Still, favorite habitats emerge.  Most notably, the only species likely to be more abundant in mature chaparral than Bewick’s Wren are the Wrentit and Spotted Towhee.

Gleaning from leaves and probing into crevices, Bewick’s Wrens ingest insect adults, eggs, and larvae as well as other arthropods and small invertebrates. They seldom feed more than 10’ off the ground and may even forage on the ground, flipping dead leaves and twigs in areas of sparse vegetation.

As a breeder, the Bewick’s Wren seems a bit of an enigma at first glance:  an obligate cavity nester often choosing chaparral and sage scrub, where no trees provide cavities.  Bewick’s Wrens certainly will use typical natural or secondary cavities (e.g., old woodpecker holes) or human-built nest boxes. Yet a broad and flexible definition of “cavity” opens a world of surprising nesting spots in otherwise unlikely environments: rocks, caves, holes in the ground, and the detritus of humanity such as a cast-off hubcap or a discarded coffee can.  Once the pair agrees on an adequate cavity, both sexes build the nest. Clutch size ranges from 3−8 eggs, which the female incubates 14−16 days. Young fledge 14−17 days after hatching.  Bewick’s Wrens commonly double-brood, if the first brood fledges early in the season. Youngsters remain together, fed by parents, for a couple of weeks after fledging.

Part of the Bewick’s Wren’s scientific name, Thryomanes bewickii, has an odd origin, at first blush.  Thryomanes means “reed lover” (from Greek thruon, “reed or rush,” and manes, “passionately fond of”).  However, this bird doesn’t inhabit moist areas where reeds grow.  Rather than implying a preference for a reed habitat, though, the genus name may instead suggest an affinity to the genus Thryothorus (e.g., the similar-looking Carolina Wren), which can indeed be found in reeds.  Bewickii honors Thomas Bewick (pronounced like the General Motors car), an English wood engraver who made plates for several natural history works.  The word “wren” arises from Anglo-Saxon warenna, their term for this type of bird.

In winter, Bewick’s Wren is even more widespread in San Diego County than during the breeding season and the male’s song, albeit varied, can help you find him.  Not many birds sing full-throated songs outside of breeding season:  White-crowned and Song Sparrows as well as California Thrashers are among the other well-known winter songsters in our area. So if you find yourself in possible Bewick’s Wren territory and hear a brightly musical song that you can’t quite place, start looking for the lively Bewick’s Wren.