Wrens tend to be a retiring and secretive family. This is by no means universal—the large cactus wrens of the genus Campylorhynchus are noisy, uninhibited, and conspicuous—but most wrens tend to spend most of their time in the lower levels of dense vegetation, going about their daily lives with an immense busyness, but liable to disappear from view at the slightest disturbance. This is especially true of the nightingale wren (Microcerculus marginatus), which is legendarily difficult to observe. Wrens are almost always first detected by song. Wren vocalizations are loud beyond all proportion to the size of the bird; some tropical wrens are stated to have a vocal production ten times louder, weight for weight, than the crowing of a cockerel. Indeed, the name for the house wren in the Ojibwa language of western Ontario means "he who makes a lot of noise for his size." Many species of tropical wrens, especially in the genera Campylorhynchus and Thryothorus, have developed elaborate, mutual songs by both sexes. In some cases these are duets, with both birds singing simultaneously. More often, though, they are antiphonal, with each sex singing a different part. The contributions often are so tightly interwoven that the casual observer would not guess that more than one bird was involved.

Another peculiar fact of wren behavior, widely spread among several genera, is the destruction of eggs of other birds, sometimes of their own species, but frequently of others. In the marshland communities of Canada and the United States, the marsh wren (Cistothoruspalustris) may destroy enough eggs of the much larger red-winged and yellow-headed blackbirds as to have a significant effect on their breeding success. Marsh wrens can, in fact, be caught in traps baited with small eggs.

A Carolina wren (Thryothorus ludovicianus) with chicks at its nest. (Photo by R. & S. Day/VIREO. Reproduced by permission.)

The decline of the Bewick's wren in eastern North America has been correlated to the increase in the population of the house wren (aided, ironically, by the provision of nest-boxes). Two closely related Campylorhynchus wrens, the giant wren of southern Mexico and the bicolored wren of northern South America have the local name Chupahuevo, literally, egg-sucker, acquired apparently by their depredations in hen houses. The function of egg predation is not clear; it may reduce competition on the nesting-ground. Sometimes destroyed eggs are eaten, but frequently they are simply punctured and left.

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