Marsh wrens are small North American songbirds. Adults have brown upperparts with a light brown belly and flanks and a white throat and breast. Their back is black with white stripes. They have a dark cap with a white line over the eyes and a short thin bill.
Marsh wrens are native to Canada, Mexico, and the United States. In the western United States, some birds are permanent residents. Other birds migrate to the southern United States and Mexico. The breeding habitat of these wrens includes marshes with tall vegetation such as cattails and bulrush. In winter they can be found in both freshwater marshes and salt marshes and in brushy edges of ponds.
Marsh wrens are usually seen alone or sometimes in pairs. They are active diurnal birds that constantly move near or on the ground searching for food. They forage in vegetation close to the water, occasionally flying up to catch insects in flight. They may also pick insects from the water surface. Marsh wrens are known for the males' loud song. The song is a loud gurgle used to declare ownership of territory and is often sung day and night.
Marsh wrens are polygynous, meaning that the males mate with more than one female. The nest of these birds is an oval structure attached to marsh vegetation, entered from the side. The male builds many unused or "dummy" nests in his territory. A hypothesis of the possible reason why males build multiple "dummy" nests in their territory is that they are courting areas and that the females construct the "breeding nest", where they lay the eggs in. The male may puncture the eggs and fatally peck the nestlings of other birds nesting nearby, including his own species (even his own offspring) and Red-winged blackbirds, Yellow-headed blackbirds, and Least bitterns. The female typically lays 4 to 6 eggs and incubates them alone for 12-16 days. The chicks hatch altricial (helpless) and usually fledge after about 13-15 days. They remain with their parents for a further 2 weeks after which the young become independent and the female starts to lay the second brood.
Marsh wrens are still common and widespread, however, their numbers have declined with the loss of suitable wetland habitat. The wholesale draining of marshes might also lead to the local extinction of some populations in the future.
According to the All About Birds resource the total breeding population size of the Marsh wren is 9.4 million birds. Currently, this species is classified as least Concern (LC) on the IUCN Red List and its numbers today are increasing.