Birds
Wren
Troglodytidae · also called wrens
A wren is one of the smallest birds in its range and, by weight, one of the loudest animals of any kind. A ball of brown feathers with a stub of a tail cocked straight up, it creeps mouse-like through the darkest tangles of a hedge or wood, then stops and delivers a song so powerful it seems impossible the bird does not fall off its perch.
Overview
Wrens are the family Troglodytidae, about 88 species, and all but one live in the Americas — the exception, the Eurasian wren, crossed the Bering land bridge and became the wren of the Old World. They eat small invertebrates hauled out of leaf litter, root tangles, and log piles, and they favour dense low cover in nearly every habitat.
Loud beyond reason
A wren weighs about 10 grams, yet its rapid, vibrant, trilling song is among the loudest of any bird for its size — the winter wren delivers over 30 notes a second, and, per unit of body weight, roughly ten times the sound power of a crowing rooster.
Nests and huddles
Male wrens build several spare “cock nests” for the female to inspect and choose from; the extras may fool predators or serve as roosts. In hard weather wrens drop their usual solitary habits and cram into a communal roost — dozens in one cavity — to share warmth through freezing nights.
Status
Least Concern — the common wrens are among the most abundant birds in their ranges, though numbers crash and rebound with hard winters. Several island and marsh specialists, like the Zapata wren of Cuba, are Endangered or Critically Endangered.
Wren: common questions
Why is the wren's tail always sticking up?
The cocked tail is simply the wren's normal posture, held up at a jaunty angle most of the time, and it flicks the tail higher when alarmed or excited. Why wrens hold the tail this way is not fully settled, but it may aid balance as the bird works through dense tangled vegetation, or serve as a visual signal to a mate or rival in the gloom of thick cover. Whatever the reason, the upright tail combined with the tiny rounded body and whirring flight makes a wren unmistakable even in a brief glimpse.
How can such a small bird be so loud?
A wren produces sound with the syrinx, the vocal organ at the base of the windpipe, and relative to its body the wren's sound-producing muscles and air capacity let it generate a remarkably high output. Measured by power per unit of body weight, the winter wren's song is roughly ten times as intense as a crowing rooster's. The song is also delivered in a fast, continuous, high-frequency trill that carries well through vegetation, and the male often sings from a slightly raised, exposed perch to project it further.
What are cock nests?
Cock nests are the spare, unfinished nests that a male wren builds around his territory, sometimes half a dozen or more. They are neat domed structures of moss, leaves, and grass with a side entrance, but the male does not line them. When a female arrives, she is shown the nests and chooses one, which she then lines with feathers and hair before laying. The unused nests may distract predators, provide roosting sites, or simply demonstrate the male's fitness and the quality of his territory, and a strong male may pair with two or three females in different nests.
Is the wren in Britain the same as the wrens in America?
It is the same family and, in the case of the common British wren, essentially the same lineage. The Eurasian wren is descended from American wrens that crossed into Asia by way of the Bering land bridge and spread west, so Europe's one wren species is a New World bird that colonised the Old World. All the other roughly 87 wren species remain in the Americas. So an American house wren and a British wren are cousins, both small, brown, loud, and cock-tailed, but the family's centre of diversity is firmly in the Americas.