The one thing I can always count on in nature is change. Just when I think I have a pretty good handle on the ecosystem in which I live, species appear or disappear.
Growing up in the Northern Virginia suburbs, I got used to the little brown-and-gray birds that would make their nests in just about any low depression and defend them fiercely. I’d personally witnessed my 15-pound cat being driven off by a bird that weighed no more than half an ounce. These little birds were wrens – house wrens (Troglodytes aedon), specifically.
Over the past few years I began to notice that the wrens I was seeing were bigger and brighter in color. A little research revealed that these weren’t house wrens but rather a relative newcomer, the Carolina wren (Thryothorus ludovicianus). As its name implies, this species hails from the south. The state bird of South Carolina, it was rarely seen north of there until a few decades ago, when global climate change led to warmer winters.
Unlike house wrens, which live in most parts of North America in the summer but head south for the winter, Carolina wrens don’t migrate and are vulnerable to cold winters, according to Cornell Lab of Ornithology’s AllAboutBirds.org website. That means that, although they have extended their range as far north as Canada, populations north of the Carolinas can crash with one or two bad winters. Unfortunately for many species, but fortunately for these wrens, the trend overall is toward even warmer winters, with the occasional bitter one that defies the trend.
There are other wren species in Virginia, including the winter wren, which prefers damp forest, and sedge and marsh wrens, which are found more in wetlands, but none are found in as many areas throughout the state as the house and Carolina species. Early colonial writings indicate that one other cousin, the Bewick’s wren (Thryomanes bewickii), was common throughout the state but is now mysteriously vanishing east of the Mississippi.
According to the summer 2011 edition of Cornell Lab’s newsletter “Birdscope,” the range of the Bewick’s wren has fluctuated ever since John James Audubon described the species in 1821. By the 1930s they were still considered “fairly common” to “common” breeders throughout the Appalachians and Midwest, but “most of the eastern populations had essentially disappeared by the 1980s.” The reasons for its decline is unclear, but among the several causes that have been considered, competition from the house and Carolina wrens, which share the Bewick’s habitat preferences, is most often cited.
Carolina wrens are easy to distinguish from house and Bewick’s wrens. They are larger and brighter than both, with more white with buff to orange accents but share the white line over the eye with the Bewick’s.
And then there’s the song. While all the wren species here are big chatterers and scolders, the house wren has a quieter, more disorganized song, while the Carolina wren loudly sings what sounds like “tea kettle, tea kettle” over and over.
The one thing I have to say about any wren I’ve had the pleasure to observe is that they’re all creative and bold in terms of choosing nesting sites and in foraging. That was brought home recently, when I woke on a frosty morning to a Carolina wren landing on my window screen, then using it to launch itself at bugs that were caught in spider webs and crevices under the eaves of my roof. With the temperature too cold for bugs otherwise being out and about, this bird was taking advantage of what was at hand. I’m not sure how nutritious the food they found was, since it could have been trapped for weeks and totally desiccated. But I assume the wren knew what it was doing. Wrens rarely hunt for food higher than 10 feet off the ground, with fruit rounding out their diet.
When it comes to nesting sites, wrens will choose pretty much any depression that is low to the ground. Humans have expanded the nesting options from tree cavities or depressions in brush piles or among tree roots to special wren houses, boots that have been left out, potted plants, and a host of other sites. Last summer a Carolina wren pair nested in an upside-down bike helmet in a shed on the property, and I once had a cardboard shoe organizer I left in a shed that another pair turned into an apartment building over the course of several years, choosing a new compartment to nest in each year. Wrens tend to adapt their nesting spots to suit them, so they can sometimes damage potted plants, but since they are native songbirds, their nests shouldn’t be disturbed.
Carolina wren nests can be distinguished from those of house wrens by their larger, dome-like structure and side entrance. Nests of both species are constructed mostly of twigs with dried grass, feathers, moss and other soft materials – even human trash – that are readily available.
Whether you find wrens jaunty and cute or loud and annoying, it’s hard not to admire them for their courage. Any trespasser on their nest site is likely to be loudly scolded and even dive bombed.