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Cistothorus platensissedge wren

By Tanya Dewey

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    7 to 10 g
    0.25 to 0.35 oz
  • Range length
    10 to 12 cm
    3.94 to 4.72 in

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

  • Breeding interval
    Sedge wrens may have multiple broods in a breeding season. Double broods are known from some areas and these wrens may migrate south for another breeding attempt before the summer is over.
  • Breeding season
    Sedge wrens breed from May into September in North America, although the timing of breeding varies latitudinally, earlier in the northern and later in the south. Breeding season in the southern hemisphere is unknown.
  • Range eggs per season
    2 to 8
  • Range time to hatching
    13 to 16 days
  • Average time to hatching
    13.8 days
  • Range fledging age
    24 to 32 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

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. (Herkert, et al., 2001)

  • Parental Investment
  • 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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

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. (Herkert, et al., 2001)

  • 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. (Herkert, et al., 2001)

  • Anti-predator Adaptations
  • 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. (Herkert, et al., 2001)

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). (Herkert, et al., 2001)

Contributors

Tanya Dewey (author), Animal Diversity Web.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

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.

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