Cistothorus platensis

Geographic Range

Sedge wrens are migratory, breeding in south central Canada and the north central United States and wintering in the southeastern United States, including the Gulf states and eastern Texas, and northeastern Mexico. There are some disjunct, resident populations in portions of Mexico. Northern breeding populations are found throughout the Great Lakes states, including Indiana, Iowa, Minnesota, the eastern Dakotas, Ontario, and southern Alberta, Saskatchewan, and Manitoba. Breeding also occurs in portions of Mexico, Central America, and throughout South America in appropriate habitat. Northern breeding populations winter along the Atlantic coastal plain from New Jersey to Florida, throughout the Gulf Coast states, eastern Texas, and into eastern Mexico to Veracruz.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

Habitat

Sedge wrens, as their name suggests, are found in sedge meadows and other wet grasslands, such as the shorelines of ponds, marshes, bogs, and coastal wetlands. They can also be found in agricultural areas with similar qualities, such as hayfields and early successional oldfields. They prefer areas with dense cover of grasses and sedges, where they place their nests, and avoid open areas, cattail marshes, sparse vegetation, and flooded grasslands. They prefer areas with a moderate density of shrubs as well.

• Habitat Regions
• temperate temperate
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

• Wetlands
• marsh marsh
• bog bog

Physical Description

Sedge wrens are smallm, black and brown streaked wrens. They have white bellies and throats, with soft brown on the sides, breast, and under the tail. The tails have black bars. They are from 10 to 12 cm and 7 to 10 g. Males and females are alike and there is no difference in plumage throughout the year, although males may be slightly larger in some features. Sedge wrens may be confused with other wren species, including marsh wrens ( Cistothorus palustris ), house wrens ( Troglodytes aedon ), winter wrens ( Troglodytes troglodytes ), Carolina wrens ( Thryothorus ludovicianus ), and Bewick's wrens ( Thryomanes bewickii ). They are distinguished by their striped heads and backs. They can also be distinguished by their songs.

There are 18 recorded subspecies of sedge wrens, divided into 3 "groups," each of which may deserve recognition as a species. The "stellaris" group (sedge wren) is found in North America and is primarily migratory. The "plantensis" group (western grass wren) is found in western South America, from Colombia and Venezuela to Tierra del Fuego. The "polyglottus" group (eastern grass wren) is found in eastern South America, from Colombia and Venezuela through Brazil to northern Argentina.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

Many aspects of sedge wren natural history are not well studied and there is little information on how mated pairs form. It is thought that pairs form on the breeding grounds, males arrive up to 2 weeks before female to establish nesting territories. Males may have a single female mate or may attract multiple (usually just 2) females to their breeding territory.

• Mating System
• monogamous monogamous
• polygynous polygynous

Migratory populations of sedge wrens seem to have a nomadic breeding cycle. Northern breeding populations breed from May through June. Breeding then occurs in the southern United States from July into September, coinciding with the departure of northern breeding populations. This suggests that sedge wrens migrate to their northernmost breeding range for their first nesting, then migrate farther south to nest again. The later breeding season could also be late arrivals or an adaptive response to habitat quality in the southern portion of the range.

Females arrive on the breeding grounds after males and nest building begins within 2 weeks after male arrival. Males build several globular nests made of grasses and then females choose among them and line them with fine materials. Nests are built in dense stands of sedges or grass, in small shrubs, or on the ground at the base of dense vegetation. Nest height above ground ranges from 10 to 100 cm. Nests take 7 to 8 days to build, duplicate nests may be predator decoys or can be used by secondary female mates. In one study males had an average of 7.4 nests in their territories. Sedge wrens attempt single broods in some areas, but observations of double broods are reported from other areas. Monogamous pairs have a higher likelihood of attempting 2nd broods. Females lay 2 to 8 smooth, white eggs, laying 1 egg each day while they are lining the nest, and begin incubating at the last egg laid. Incubation is for 13 to 16 days and the young fledge at 11 to 16 days after that (usually 12 to 14). Young sedge wrens become independent some time after fledging, although how long they remain dependent on females after fledging is unknown. It is likely that sedge wrens breed in their first year after hatching, as do other wrens.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Females incubate the young, which are born naked and helpless. Their eyes open at 4 days and they fledge at 11 to 16 days old. Young of secondary females lag behind the young of primary females in development. Females also provide all food for the young, although males may occasionally help. The young remain near the nest and are fed by their mother for some time after fledging. Males contribute to territory defense, so may help to protect young from predators.

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

Lifespan in sedge wrens is not known, no banded sedge wrens have been recovered. Nests and adults are destroyed during hay and rice harvesting and by cattle trampling in pastures. Sedge wrens have also been reported colliding with towers during migration.

Behavior

Sedge wren populations in North America are short-distance migrants. Northern populations begin migrating northwards in April and May. These populations have also been described as nomadic, as some migrate to northern breeding areas in the spring, then migrate to more southern portions of the breeding range in late summer and breed again there. Sedge wrens begin their southwards, fall migration in August through October. They seem to migrate in mixed-species flocks with other wrens . They migrate at night. Sexes from northern breeding populations seem to occupy different winter ranges, with females occurring farther south than males. Sedge wrens do not have high breeding site fidelity, and may be nomadic during the breeding season in North America. Fidelity to wintering sites is not known.

Sedge wrens are secretive birds. When startled, they run along the ground for a short distance before taking flight, then fly a short distance before diving into the cover of vegetation again. Sedge wrens are active during the day and either occur in pairs or in mixed-species flocks during migration. Their winter habits are not known.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• migratory migratory
• sedentary sedentary
• social social

Home Range

There is no information on territory size or home range size in sedge wrens. Nest density has been reported from 1 to 68 males per 10 hectares, with density varying by habitat type. Higher densities are found in sedge meadows and grasslands, lower densities are found in tallgrass prairies.

Communication and Perception

One of the few natural history aspects of sedge wrens that have been well studied are their vocalizations and much is known about song development. Sedge wren males develop from 29 to 63 individual song types through improvisation. Songs are not strictly learned or imitated from songs encountered in their environment, rather they are improvised by individual males to be unique. This is in contrast to closely related marsh wrens ( Cistothorus palustris ), which use songs primarily learned from the environment. Patterns seem to differ in resident populations of sedge wrens in Central and South America, where there is more evidence of song learning or imitating nearby conspecific males, rather than improvisation. Only males sing, they begin developing song as fledglings, but then cease singing until the following year, when they develop their song repertoire.

Songs have been described as "staccato chattering." All sedge wren songs begin with a stereotyped set of 3 to 4 notes, followed by various trills that vary individually. Marsh wren calls can be distinguished because of their more musical quality and less emphasis on the initial, stereotypes portion of the song sequence. Males may begin to sing on their wintering grounds in the spring, but their arrival on breeding grounds is generally discovered through the detection of singing males. Males sing from perches, usually, but will sing at other times as well. Males repeat individual song types on average 19 times before switching to another song type, although this varies substantially. Social context changes how frequently males change between song types and how many types of songs they use. Competition with nearby singing males tends to increase the number of songs and the number of types of songs expressed.

• Communication Channels
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Sedge wrens are invertivores, eating mainly insects and spiders. There is little information on details of their diet or foraging because of their cryptic habits, but a few observations suggest they mainly forage on the ground near the bases of grasses and sedges. Some stomach content analyses suggest that sedge wrens eat large proportions of spiders , along with ants , weevils , lady beetles , butterfly and moth larvae , and grasshoppers .

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • eats non-insect arthropods

• Animal Foods
• insects
• terrestrial non-insect arthropods

Predation

Sedge wren nests seem to be heavily preyed on, predation is the dominant reason for nest failure in some areas. However, few predators are reported. Red foxes are known to take sedge wrens. Responses to predators are unknown, but sedge wrens are cryptically colored and behave secretively.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Sedge wrens prey on invertebrates and are likely to be preyed on by small, terrestrial and avian predators. There are no reported parasites or diseases.

Economic Importance for Humans: Positive

Sedge wrens are unique members of wet grassland ecosystems throughout the Americas.

Economic Importance for Humans: Negative

There are no adverse effects of sedge wrens on humans.

Conservation Status

Sedge wren populations shows small increases between 1966 and 1996, but sedge wrens have suffered from the loss of mesic grasslands throughout their range and local populations have experienced declines as a result. Wet grasslands are frequently drained and converted to agriculture, making them less suitable for sedge wrens. Also, grazing, burning, and mowing, sometimes used to manage grasslands for other species, negatively effects sedge wrens because they prefer tall, dense grasslands. Overgrazing and burning in Argentina have resulted in severe population declines of sedge wrens. They are considered "least concern" by the IUCN because of their wide range, large estimated population sizes, and lack of evidence for substantial population declines. However, the U.S. Fish and Wildlife Service considers them a U.S. migratory species of concern and they are listed as endangered, threatened, or special concern in 9 eastern and midwestern United States, including Pennsylvania, Massachusetts, New York, and New Jersey. Their erratic and seasonal occurrence in areas makes it difficult to accurately assess population sizes. Populations seem to do well in years with lots of precipitation.

Other Comments

Sedge wrens were previously called "short-billed marsh wrens" but the name was changed to distinguish them more from marsh wrens ( Cistothorus palustris ). Sedge wrens are considered closely related to several South American Cistothorus species with localized distributions: Merida wrens ( Cistothorus meridae ) and Apolinar's wrens ( Cistothorus apolinari ).

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (author), Animal Diversity Web.

References

Herkert, J., D. Kroodsma, J. Gibbs. 2001. Sedge Wren (Cistothorus platensis). Birds of North America Online , 582: 1-20. Accessed May 21, 2009 at http://bna.birds.cornell.edu/bna/species/582 .