The marsh wren (Cistothorus palustris) is a small, secretive songbird that is well known for its melodious song and energetic behavior. There are several unique features that distinguish this species from other wrens and make it well-suited for life in marshes and wetlands across North America.
Size and Appearance
The marsh wren is a relatively small wren, measuring only 10-13 cm (4-5 inches) in length and weighing approximately 10-12 g (0.35-0.4 oz). It has a short tail, rounded wings, and a thin, needle-like bill. Its plumage is mostly brown above and light brown to cinnamon below. The marsh wren has pale stripes over its eyes and brown and white bars on its wings and tail.
One of the most distinctive features of the marsh wren is the dark crown stripe on the top of its head. This stripe is always present, though it may be hidden when the wren flattens its crown feathers. The coloration of the stripe can vary geographically from blackish-brown to rufous. This crown stripe helps distinguish the marsh wren from other similar wren species like the sedge wren.
Male and female marsh wrens are mostly identical in appearance. Juveniles resemble the adults but have paler underparts and may lack the crown stripe until their first molt.
Habitat
As its name suggests, the marsh wren is strongly associated with wetland habitats, particularly freshwater marshes. More specifically, it prefers areas of dense emergent vegetation interspersed with areas of shallow, open water. Typical nesting and foraging locations include:
- Cattail marshes
- Sedges and rushes
- Reed beds and wet meadows
- Irrigation ditches
- River and lake edges
The marsh wren generally avoids brackish or saline wetlands. It prefers wetlands with shallow, slow-moving water that does not completely inundate the vegetation. This species is not often found far from some type of wetland habitat.
Nest Building
One of the most unique features of the marsh wren is the large, globular nests that it builds out of wetland vegetation. The nests are constructed entirely by the male and are placed in tall reeds, cattails, or shrubs within or just above standing water. The nests are made of woven grasses and sedges and have a side entrance hole to allow access.
A male marsh wren may build up to a dozen or more unused “dummy” nests in his territory, in addition to the breeding nest. The purpose of these extra nests is believed to be to provide safe roosting and resting sites and also serve as decoys to distract predators from the active nest. Males with more dummy nests tend to attract more females.
Song and Calls
The marsh wren is a bold and vocal species renowned for its complex, melodious song. The song consists of a gurgling jumble of rich, varied notes, trills, and whistles. It has been described poetically as resembling a “bubbling splatter of jewels”. The male sings persistently through the breeding season and may deliver hundreds of songs per day.
In addition to its elaborate song, the marsh wren uses various calls to communicate, including a sharp “chit” alarm call and a low-pitched “zeee” contact call. Males and females engage in duets of whining “pee-err” calls to solidify pair bonds and defend territories.
Diet
Marsh wrens are omnivorous and opportunistic in their feeding habits. Their diet consists mainly of small insects and other invertebrates. Some common prey items include:
- Spiders
- Dragonflies and damselflies
- Beetles
- Flies
- Bees, wasps, and ants
- Moth and butterfly larvae
They supplement their diet with small amounts of seeds and berries when available. Marsh wrens forage energetically through dense reed beds and cattails, climbing and hanging upside down to probe for food. Parents also deliver insects and spiders to their nestlings.
Breeding and Nesting
The breeding season for marsh wrens spans spring and summer, generally from May to August across their range. Males establish breeding territories centered around areas of dense emergent cover and build several dummy nests as well as a nest for breeding.
Females build a cup-shaped lining inside the globular nest. Clutch sizes are typically 5-6 eggs but may contain as many as 10. The female incubates the eggs for 12-15 days. Both parents feed the young, which leave the nest at 15-18 days old but are still dependent on their parents for 2-3 more weeks.
Marsh wrens are solitary nesters and maintain well-defended territories. However, suitable habitat often occurs in patches close together, leading to high nesting densities in optimal marsh habitat. Males may take multiple mates over the course of a breeding season.
Migration
The marsh wren is migratory across most of its range. Northern populations migrate south to the southern United States, Mexico, and the Caribbean for the winter. Migration occurs from September to November in the fall and April to May in the spring.
Some southern populations in the U.S. along the Atlantic and Gulf Coasts are permanent residents. Marsh wrens also overwinter as far north as the Great Lakes region where open water persists.
Conservation Status
The marsh wren has a very large range and global breeding population estimated at 19 million birds. Its populations appear to be stable, and it is classified as a species of Least Concern by the IUCN Red List.
However, local and regional declines have occurred in areas where wetlands have been drained or degraded. Maintaining suitable habitat across the marsh wren’s range, particularly in migration and wintering areas, is important for the continued health of this species.
Fun Facts
- A male marsh wren may build up to 15 dummy nests per breeding season in addition to 1-2 breeding nests.
- The marsh wren was once called the “long-billed marsh wren” to distinguish it from the sedge wren, which was known as the “short-billed marsh wren”.
- Marsh wren nests occasionally house the eggs of brown-headed cowbirds, which parasitize the nest and leave their eggs for the wrens to raise.
- Marsh wrens live an average of 1-3 years but the longest known lifespan in the wild is 5 years.
- The marsh wren walks and runs more than other wrens, bobbing its tail up and down in characteristically wren-like fashion.
Conclusion
The marsh wren is a remarkably unique bird that has evolved special adaptations for life in its wetland habitat. Key identifying features include its size and markings, its preference for dense emergent wetlands, elaborate domed nests, rich bubbly song, and active foraging lifestyle. This species plays an important role as an insect-eater in wetland ecosystems across North America.
Understanding the marsh wren’s specialized habitat needs and maintaining suitable wetlands will be crucial in ensuring the continued success of this species. Its large population size and extensive range are encouraging, but local declines serve as a reminder that this unique wetland songbird still faces threats from habitat loss and degradation.