From its name, one might reasonably expect that the Carolina wren — Thryothorus ludovicianus — is a bird of the south. That’s certainly true in part; Carolina wrens are common in the Carolinas and across the southeastern US. However, these feisty little birds have been well established in Ohio’s southern counties since at least the late 1800s, and today they are common throughout the state.
Southwest Ohio is home to five species of wrens. All of them are small, brown birds, characteristically perching with their tail in a cocky upright posture. With their camouflaging coloration and habit of searching for food among the undergrowth, Carolina wrens can be a challenge to spot. However, they also can be bold and obvious at times, as they sing loudly from exposed perches or confront intruders with pugnacious chatter.
Of Ohio’s wren species, Carolina wrens are the only year-round residents. Three of the other four species migrate south out of Ohio for winter and one species, the winter wren, migrates south into Ohio. Year-round residency provides opportunity for an extended breeding season. Carolina wrens build a domed nest, typically within an enclosed space like a set of roots, a tree hole, or (sometimes) a mailbox or hanging plant. That nest structure provides good protection from the elements, and Carolina wren nests have been observed in Ohio as early in the year as early April and as late as December. A single pair might raise two or three broods in a single season.
Male Carolina wrens pack a remarkably loud voice into a small body, and they sing loudly and persistently when they are on a nesting territory. The song commonly includes a repeated three-note phrase, with something like two dozen variations, often described as “tea kettle, tea kettle, tea kettle” (but also as “come to me, come to me, come to me,” or “liberty, liberty, liberty,” or many other variations). An individual male might belt out 3000 of those phrases per day. Carolina wrens start their singing early; a wren nest near one’s house provides a reliable morning alarm clock!
Carolina wrens do have a couple of interesting twists to their singing repertoire. First, while males sing most persistently during the breeding season, they actually sing year-round. Songs during the breeding seasons are slightly longer and more complex, but otherwise they are structurally similar across the year. This likely reflects the fact that males are territorial all year long, and singing is an important part of defending a good territory. A second feature is that although female Carolina wrens don’t sing, they produce a variety of chirring phrases that, sometimes, are coordinated with a male’s singing. That partnership represents a rudimentary version of a phenomenon called duetting. Many tropical wrens (and other birds) engage in rich, more complex vocal duets. Carolina wrens have evolved from tropical ancestors, but the female component of the behavior has largely been lost.
The diet of Carolina wrens is mostly insects and spiders. During cold weather, meeting their energy needs would require each bird to eat something like two-thirds of its body weight in insects per day. Wrens do continue to hunt for bugs during winter by scouring among loose bark and fallen leaves. However, with insects less available, they also expand their diet to include nuts and fruits. Carolina wrens readily come to bird feeders. Though they might sound like they’re calling for “cheeseburger, cheeseburger, cheeseburger,” what they really seem to treasure is hulled peanuts.
The combination of year-round residency and reliance on insects or low-lying foods means that Carolina wrens are particularly susceptible to impacts from snow, especially when it’s deep and persistent. In one large-scale study, each additional day of snow cover during winter–spring was associated with a 1.1% decline in the population of wrens. Ohio’s blizzards in the late 1970s extirpated the species from several counties. The population has rebounded, with fluctuations, in the decades since.
Although winter is a hazardous time, the birds that do survive are the ones that figure out how to find adequate food and shelter during cold weather. Gradually, evolution of those traits, along with warming at northern latitudes and increasing availability of winter bird feeders, has allowed Carolina wren populations to expand northward. They now breed commonly in every Ohio county. Northward range expansion seems to be occurring for a number of bird species that are year-round residents in temperate North America. In contrast, species that migrate south for the winter may encounter stresses of long-distance flight and degraded winter habitat; their populations are more likely to be in decline.
In the Star Wars universe, Kylo Ren was a dark side warrior. Carolina wrens might seem to have a few characteristics in common with Kylo — they are bold, charismatic, sometimes brash to the point of aggressive. But while Kylo Ren’s good side was suppressed, Carolina wrens seem to bubble over with joy. Just give them opportunities for shelter — a brush pile, some shrubbery — and a stocked birdfeeder, and you will enjoy the pleasure of their company. May the Thryothorus be with you!
Article and photo contributed by Dr. David L. Goldstein, Emeritus Professor, Department of Biological Sciences, Wright State University.