Systematics
There are two distinct groups of Marsh Wrens in North America and 14 subspecies. The two groups are divided into eastern and western populations largely on the basis of vocal characteristics, although there are differences in color, pattern, size and molt (Kroodsma and Verner 1997).
Perception Channels: visual ; tactile ; acoustic ; chemical
Habitat degradation is the greatest threat to Marsh Wren vitality, although some migrants are killed every year in collisions with communication towers and other structures. Destruction of marshes and wetlands used by Marsh Wrens as breeding or wintering grounds results in a great reduction in numbers in the area. Marsh Wrens readily colonize newly created or restored wetland habitats, however, resulting in increasing population sizes in some areas (e.g. high numbers of Marsh Wrens were found in marshes created by dam construction along the Colorado River) (Kroodsma and Verner 1997). Marsh wrens are a species of special concern in Michigan.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: special concern
IUCN Red List of Threatened Species: least concern
Conservation concerns may prevent development of wetland habitat.
Unknown.
Marsh Wrens mainly eat invertebrates, especially insects (e.g. bees, ants, wasps, beetles, and moths) and spiders as well as aquatic invertebrates in freshwater marshes. Foraging occurs on or near the marsh floor; Marsh Wrens glean insects from stems and leaves of vegetation and the water's surface. Some birds may forage in thickets or shrub patches that occur near the marsh (Kroodsma and Verner 1997).
The breeding range of the Marsh Wren (Cistothorus palustris) extends west from the Atlantic coast to Nebraska and North from southern Illinois to northwestern. In the western United States C. palustris is a year round resident. There are also breeding and resident populations along coasts of the southern Atlantic and Gulf states. The wintering range extends south from the southwestern states of New Mexico, Arizona and Texas and into Mexico; Florida is also a wintering ground for Marsh Wrens (Kroodsma and Verner 1997).
Biogeographic Regions: nearctic (Native )
Marsh Wrens use a variety of wetland habitats. Cattails and bulbrush is the vegetation that dominates most Marsh Wren habitat. This wren occurs in salt and brackish marshes in addition to freshwater sites. The habitat of the winter range is similar to that of the breeding range (Kroodsma and Verner 1997).
The Marsh Wren is a small wren, ranging from 10.4 and 14.0 cm in total length and weighing between 9.0 and 14.0 grams. Males and females have similar plumage. This species has a black crown, white superciliary stripes, warm-brown upperparts with faint black bars, a black and white striped triangular region on the upper back, buffy sides and breast, whitish below, and dark barring on the tail. Marsh Wrens have brown eyes, pale brown feet and legs, and a brownish bill. Males are larger than females, though body size varies geographically. Juvenile plumage is similar to adult plumage except there are fewer black markings on back, the superciliary stripe is faint or absent, and wings are only faintly barred (Kroodsma and Verner 1997).
Range mass: 9 to 14 g.
Other Physical Features: endothermic ; bilateral symmetry
Marsh Wrens are polygynous, but the percentage of males mating with more than one female varies among populations (e.g. in Georgia 5% of males had more than one mate, while 41-54% of males in Manitoba had more than one female). Timing of pair formation is variable depending on population and year. Males begin singing within one to two days of their arrival on the breeding grounds. In migrant populations females usually arrive on breeding grounds seven to ten days after males and then mate with males a few days after their arrival.
Males build numerous, single-opening dome-shaped nests on their territory prior to female arrival. Female choice is dependent upon territory quality and nesting status of other females (i.e. females tend to prefer unmated males). When a female approaches a male's territory he flies over to her and sings. If she enters his territory the male will show her several nests he has constructed, and if she chooses to mate with the male she may line a nest with strips of grass, small stems, cattail downs, feathers and rootlets or she may build an entirely new nest (Kroodsma and Verner 1997).
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
