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Wildlife Note

Wrens are small, active birds, basically brown in color, that often perch with their tails held straight up in the air. They forage on or just above the ground in thick brush, forest understory, or marsh vegetation. Wrens belong to the Troglodytidae family, with about 70 species in the New World, most of them in the tropics. Only one species lives in the Old World: the winter wren, which likely spread from North America to Eurasia spreading from Siberia to Britain and Iceland.

Some wrens nest in cavities, while others build roofed structures out of plant matter. The males of several species build “dummy” nests, preliminary nests placed in tree cavities, woodpecker holes, nest boxes and less frequently in odd enclosed spaces like tin cans, hats, boots, flower pots and drainpipes. Later, a female will choose one of the male’s dummy nests, finish its construction, and lay eggs in it. Wrens often pester other birds and evict them from nest cavities, puncture their eggs, or peck their young to death. They destroy nests in cavities and in the open. They also wreck other wrens’ nests. Why such belligerence? Perhaps, an abundance of empty nests discourages predators from looking further and finding an active wren’s nest. Or perhaps killing its rivals’ offspring reduces pressures on prey populations, making it easier for a wren to feed its own young.

Wrens mainly eat insects and spiders. A few species will also feed on berries and seeds. Owls, small hawks, foxes and house cats take adult wrens. Raccoons, opossums, mink, weasels, mice, squirrels, woodpeckers and snakes raid wrens’ nests. Some wrens migrate southward in winter, while other species remain as permanent residents on their breeding range. Five species are found in Pennsylvania.

Carolina Wren (Thryothorus ludovicianus)

The Carolina wren inhabits the eastern United States stretching north into southern New England and southeast Ontario and south into eastern Mexico, Guatemala and Belize. It is a permanent resident wherever it breeds. At 5½ to 6 inches long, and weighing 0.7 ounces, it is the largest of the Pennsylvania wrens. Carolina wrens are colorful birds with rusty brown upper plumage, a buffy or cinnamon breast, and a white stripe above each eye. They also have “colorful” personalities that provide a lot of entertainment for human observers. They prefer moist or bottomland woods with moderate to dense shrubby or brushy cover. They also inhabit gardens and yards. Carolina wrens forage mainly on the ground, often near downed trees or brush piles, using their curved bills to lift up leaf litter and snatch prey. They can climb up tree trunks like creepers or nuthatches.

Carolina wrens eat mainly insects and spiders. They catch caterpillars, chinch bugs, beetles, leafhoppers, grasshoppers, crickets, katydids and many other insects. They may also eat seeds of poison ivy, sumac, smartweed, and other herbaceous plants, plus fruits and acorn mast. Carolina wrens will visit feeders, pecking at suet and picking raisins, mealworms or other offerings.

The Carolina wren is monogamous and mates for life. Pairs often forage together and defend a territory year round. The species has a clear, ringing song, tea-kettle, tea-kettle, tea-kettle, which it may give year-round. Carolina wrens nest in tree cavities, bird houses, crevices in stone walls, among exposed roots and in cracks in buildings. Carolina wrens can cause amusement or consternation of their human hosts by building nests in a variety of odd places like gutters, hanging plants, stored boats and canoes, clothes pin bags, cans of nails, open tool boxes and the nooks and crannies of sheds, porches, and garages. Using leaves, twigs, and other plant materials, both sexes build a dome shaped nest with a side entrance. The normal clutch is five or six eggs. Incubation is by the female and takes 12 to 16 days. The male feeds her on the nest. The young leave the nest about two weeks after hatching. Pairs usually raise two broods per year.

In the last century, the Carolina wren has been expanding northward. Pennsylvania is on the northern edge of the species’ breeding range, which extends north after mild winters and ebbs south following harsh winters. Extended periods of ice and snow can devastate local populations.

Bewick’s wren (Thryomanes bewickii) is a similar appearing species that bred in southern Pennsylvania until around 1976. Since then, it has disappeared. Bewick’s wren is listed as an extirpated species in Pennsylvania.

House Wren (Troglodytes aedon)

The most common wren in Pennsylvania, this bird was named because it often lives around humans’ dwellings. A house wren is five inches long and weighs a third of an ounce. Its overall color is gray brown. House wrens live in open shrubby woodlands, small woodlots, woods edges, towns, suburban backyards, and city parks. They feed on insects, spiders, millipedes, and snails. The species breeds across southern Canada and the United States. House wrens in the northern parts of their range migrate south to spend the winter in the southern United States and Mexico.

Males arrive on the breeding grounds in late April or early May. They establish territories of one half acre or larger and advertise for females with a rich, liquid song. Males build dummy nests out of twigs in tree cavities, nest boxes, or hollow fence posts; one male may construct up to seven such nests, defending them and the space around them. When building dummy nests, house wrens may destroy the nests and young of tree swallows, chickadees, bluebirds, and prothonotary warblers. House wrens often nest in boxes intended for bluebirds that are positioned close to shrubs or trees. Females either arrive later than the males or stay hidden in brush until they begin inspecting the males’ territories. If a female finds a territory to her liking, she will finish one of the male’s dummy nests by adding a lining of grass, plant fibers, rootlets, feathers, and animal hair.

In late May or early June, the female lays five to eight eggs, which are white and speckled with reddish brown. She incubates them for twelve to fifteen days. After the eggs hatch, the male helps with feeding the young, bringing grasshoppers, crickets, caterpillars, and spiders to the growing nestlings. About two weeks after hatching, the young leave the nest. Females typically produce one to two broods. A female may abandon her first brood soon after the young have fledged, leaving the male to rear them. He may then move to another male’s territory, mate again, and lay a second clutch. A male house wren may mate with two or more females in his territory, although he will usually help only the primary female raise her young. A “floater” is an unmated male who enters an established territory and tries to drive away the resident male or mate with the female. If he succeeds in taking over a territory, he may destroy the female’s eggs or young. At that point, she will usually renest.

Most house wrens leave the breeding range in September and early October. They migrate by night. Some are killed when they collide with communications towers. On their southern wintering grounds, they forage in thick brush. The oldest house wren on record lived nine years, but most individuals probably survive for only a year or two. Ornithologists believe the species has been expanding southward since European settlement began. The house wren benefits from forest fragmentation and does well in towns and residential areas.

Winter Wren (Troglodytes hiemalis)

At just over four inches in length, the winter wren is Pennsylvania’s smallest wren. Its plumage is dark brown, and its tail is stubby. Unlike the similar house wren, the winter wren is a bird of forests and not usually found near human habitations. The winter wren is strongly associated with hemlocks and is an indicator species for high quality forests. Look for this secretive bird in deep woods, particularly old growth conifers, where it forages in low shrubs, tangled roots of downed logs and shady ravines behaving “more like a mouse than a bird,” notes ornithologist Kenn Kaufman. The male’s song is a very loud and complex series of warbles and trills, one of the most remarkable of Pennsylvania bird songs. Foods include insects, spiders, small fish taken from stream shallows, and berries. In the East, winter wrens breed from Newfoundland south to Georgia in the Appalachians. They nest in cavities, and a brood of five to six young is the norm. Males may mate with more than one female. Populations in Pennsylvania have been growing in recent years according to breeding bird surveys with a more than twofold increase between the first and second atlas projects. Winter wrens head south in early fall, although some remain in the north and winter along streams and in swamps. Some are reported during Christmas Bird Counts in Pennsylvania.

Sedge Wren (Cistothorus platensis)

This small (four and a half inches), shy wren inhabits moist upland sedge meadows with little or no standing water. It was formerly known as the short-billed marsh wren. Sedge wrens often breed in small colonies. They may occupy a suitable habitat for several years, then disappear. Some sedge wrens move into the state after nesting in the Mid-western states, reacting to drought. Some have attempted to nest in wet hayfields as well as “proper” marshland and meadows. Males sing a dry, rattling song. They can form small “colonies” of nesting pairs. Hal Harrison once counted 35 to 40 singing males on a 10-acre site. The actual nest is a ball of dried or green sedges woven into growing vegetation two to three feet above the ground. The usual clutch is seven eggs. A female generally produces two broods per year, and males may mate with more than one female. Breeding bird studies have shown that the sedge wren is a rare and local breeder in Pennsylvania and declining in parts of the Northeast. The sedge wren is listed as an endangered species in Pennsylvania because of its extreme rarity as a nesting species

Marsh Wren (Cistothorus palustris)

This is the typical wren of the cattail marsh. It is four and a half to five and a half inches long. Its brown plumage is marked with black and white stripes on the back and a white eye stripe. Marsh wrens arrive on the breeding range in late April or early May. The male’s song is reedy and gurgling, lasts one to two seconds, and is given up to twenty times per minute, by day and at times by night. Not particularly musical, it reminded one naturalist of “air bubbles forcing their way through mud or boggy ground when trod upon.”

The marsh wren forages on the marsh floor, flitting up and clinging to stalks and leaves of cattails, bulrushes, and other plants while searching for prey. It gleans aquatic insects and their larvae, other insects, spiders, and snails from vegetation and often nabs larvae from the surface of the water. Both males and females will peck and destroy the eggs of other birds in their territory. Red-winged blackbirds often attack marsh wrens on sight. Males typically build dummy nests ¬around six for each breeding nest used by a female. The female weaves an oblong nest out of cattails, reeds, and grasses, secured to standing vegetation. A short tunnel leads to a central cavity in which three to six eggs are laid. The female incubates the clutch for about two weeks. Fed by both parents, the young fledge after twelve to sixteen days. The adults care for them for another two weeks. One to two broods are produced each year. Male marsh wrens are polygamous. Up to half of all breeding males may mate with two or more females. Marsh wrens in the East winter along the Atlantic and Gulf coasts.

Marsh wren populations have sharply declined over several decades. They occupy fewer wetlands than in decades past, raising concern for their status in the state. The decrease in the size and quality of wetlands has had a negative impact on this small wetland bird and even more on larger wetland species like bitterns and rails. The marsh wren is listed as a species of High Level Concern in the state Wildlife Action Plan.