Carolina Wren

The Carolina Wren is one of the more recent southern invaders to expand into New Hampshire. It was extremely rare in the state until the 1990s, occurring only as a vagrant or occasional winter visitor, and was not confirmed nesting until the early 1990s. For the next two decades it remained uncommon and restricted to lowlands in the southern part of the state. All this changed rather dramatically starting around 2010, and in the next ten years Carolina Wrens were reported in most towns south of the White Mountains except those at higher elevation or that were mostly forested. There are now even regular reports from the southern edge of Coos County, although the species should still not be expected north of the mountains.

This expansion has probably been facilitated by two things, a warming climate and the Carolina Wren’s propensity for living near people. Throughout their gradual colonization of New England, wrens have occasionally faced high mortality during unusually cold winters, presumably a consequence of their southern origins. But the wrens who survive are just a little hardier and slowly but surely the species has adapted to the local climate – while the local climate also becomes more favorable. You still might notice the absence of a local wren after a significant cold snap, but it’s likely that another will arrive to replace it in due time. Bird feeders have also likely been important during the expansion, since a reliable food source can ensure survive over cold winter nights. A nearby shed or space beneath a porch can also provide critical shelter against the elements.

Although Carolina Wrens are obviously a successful species, living in close association with people carries some risks. Because they often forage on the ground or in low shrubs, they are vulnerable to predation by cats, and this may particularly apply to recently-fledged young. A more insidious threat is that posed by various forms of pollution. One study found that wrens in areas contaminated by mercury produced fewer young and were more likely to abandon their nests. The effects of other contaminants have not been studied, but it is likely that things like pesticides could reduce food supplies or directly compromise the birds themselves, as has been shown for other species.