Given its name, it is not too surprising that the Carolina wren (Thryothorus ludovicianus) is the official state bird of South Carolina. These little birds can also be found year-round throughout Massachusetts, though, and their range appears to be expanding. Massachusetts is at the northern end of this wren’s range, but as winters warm, these birds are making their way even as far north as Maine and Quebec.
During cold winters, the population takes a steep nosedive. Ornithologist Edward Howe Forbush first observed this phenomenon in 1929:
The Carolina Wren is nonmigratory. It stays throughout the year in its chosen location, but it is not a very hardy bird, and a severe winter will destroy most of the individuals in the northern parts of its range … During the summer after mild winters, the number of Carolina Wrens increases northward and many young or unmated birds wander into northern states. During the next severe winter most of these birds succumb to cold and starvation. As the Carolina wren gets most of its food on or near the ground, deep snow is fatal, but a succession of mild winters will favor another increase. The winter of 1903-04 was regarded at New Bedford, Massachusetts, as the most severe in the ninety-nine years in which records had been kept and the next winter was also very inclement. Undoubtedly these two winters destroyed most of the few Carolina wrens in New England. Milder winters followed … and the wrens reappeared in unprecedented numbers.
This boom-and-bust cycle continues to this day. During the winter of 2015 – remember that winter with 110 inches of snow! – Carolina wrens were hit hard in our region. During Valentine’s weekend alone, Boston had an epic blizzard with air temperatures reaching 3 below zero. Cold temperatures and deep snow stuck around for weeks, and Carolina wrens died in droves. Despite these setbacks, population in its northern range is increasing at about 1.5 percent per year.
Why are numbers increasing? One possibility is that the birds have adapted to a different diet in the winter. In the summer, 94 percent of a Carolina wren’s diet is insects. In the winter, the birds that adapt to eating seeds survive better and pass this seed-eating behavior onto their offspring. This shift in winter food preference allows Carolina wrens to take advantage of bird feeders throughout the region.
Carolina wrens are the color of cinnamon above and tan underneath. Their beaks curve down, an adaptation that helps them pluck insects from leaves and bark. Carolina wrens, like all wrens, cock their tails upright, a feature that makes it easy to distinguish them from sparrows.
Look for Carolina wrens on or near the ground, probing for hidden insects in tangled undergrowth. They especially enjoy caterpillars, moths, leafhoppers, beetles and grasshoppers. They sometimes dart up tree trunks looking for fruit pulp or spiders. When foraging for food, these little birds cock their tail upward, hopping more than they fly. They try to stay hidden in dense undergrowth.
Male Carolina wrens seem to sing anytime and anywhere. They even mimic other birds, and for this reason, are sometimes called the mocking wren. The males have a repertoire of at least 20 phrases. They choose one and repeat it for three to five minutes. People most often say their three-syllable call sounds like tea-kettle, tea-kettle, tea-kettle or come to me, come to me, come to me. When a male sings, he chooses a conspicuous location atop a bush or low tree, lifts up his head and drops his tail. He sings year-round, except in the most inclement weather. The female does not sing, although she responds with a chittering sound.
Male Carolina wrens are one of the most vocal of songbirds and use their calls and songs to establish and defend their breeding territory. These birds mate for life and are most often seen in pairs, work together to build a nest that can be almost anywhere. These birds are not choosy: They will nest in natural locations 3 to 6 feet off the ground such as tree cavities or stumps, branches or brush piles, roots of fallen trees or abandoned bird nests. But they will also nest in humanmade crannies such as mailboxes or flowerpots, boots or bicycle helmets.
Maurice Brooks wrote the following about an unusual roosting site:
My father found … a very large nest built by white-faced hornets. This nest was hung up in an out-building, and no attention was paid to it until late in the winter when we found, to our surprise, that a pair of Carolina Wrens had enlarged the opening and were using it as a nightly roosting place. The birds continued to roost there until spring, when they carefully constructed a nest of their own, in the top of the hornets’ nest, away from the opening.
Female Carolina wrens lay about four eggs, which they incubate for two weeks until the chicks hatch. Both parents bring the chicks food for another two weeks, at which point the chicks fly away. Family groups may forage together for a while, but the parents also get to work preparing for a second brood.
During the breeding season, Carolina wrens work together to build a nest and incubate eggs, but they do not necessarily roost together. During the winter, however, unlike many birds that go their separate ways, Carolina wren couples roost together. The mortality rate for Carolina wrens is highest, not surprisingly, during the winter. Roosting together the pair is warmer in the winter and safer from predators. This togetherness also reinforces their pair bonding, and the two stay together for life.
Have you taken photos of our urban wild things? Send your images to Cambridge Day and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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