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= Sedge Wren =

Introduction
The sedge wren (Cistothorus platensis) is a small and secretive passerine bird in the Troglodytidae family. It is widely distributed as it can be found in North, Central and South America. However, only the sedge wrens living in North America migrate. They are often found in wet grasslands and meadows where they nest in the tall grasses and sedges and feed on insects. There are multiple subspecies of sedge wrens, several of which could potentially be considered as separate species.

Description
The sedge wren is a relatively small wren that measures 10 to 12 cm, weighs 7 to 10 g and has a wing-chord of 41 to 46 mm. Females and males have the same plumage but males are slightly larger. Their head and back are tawny brown streaked with black and white. They have a pale buff supercilium and brown irises. . Their rump is orange and tail is tawny brown bared with black. Wings are tawny brown bared with black, white and pale buff. They have a white throat and belly with pale buff on the side. Their beak is long and slender and measures on average 6.77 to 6.95 mm. The upper mandible of the beak is brown while the lower mandible is yellow. They have pink legs and feet. Juveniles are overall similar to adults but have less streaking on the head and nape and their chest is paler than adults. The plumage can also vary between subspecies. The sedge wren can be differentiated from the similar marsh wren (Cistothorus palustris) by its smaller size, streaked crown and different song.

Taxonomy
The sedge wren was formerly known as the short-billed marsh wren but was renamed to better distinguish it from the marsh wren. The sedge wren is one of the four species within the genus Cistothorus being more closely related to the marsh wren. Recent research based on genetics, geographical range and morphology suggests that the currently recognized sedge wren species actually encompasses at least 8 distinct species.

Subspecies
Currently, there are about 18 recognized subspecies divided intro three groups based on geographic range and morphological features.

Stellaris group
The Stellaris group is the largest of the three groups with 9 subspecies. This group includes the North American and migratory C. p. stellaris as well the 8 central american subspecies.

The 9 subspecies in the Stellaris group are :

• C. p. stellaris

• C. p. tinnulus

• C. p. elegans

• C. p. lucidus

• C. p. potosinus

• C. p. jalapensis

• C. p. warneri

• C. p. russelli

• C. p. graberi

Platensis group
There are 6 subspecies in the Platensis group, all of which inhabit South America. They range from Columbia and Venezuela down to the Andes, Patagonia and Tierra del Fuego. They are also found on the Falkland Islands. They generally differ from the Polyglottus group by their larger size, barred tail and longer wing length. They also usually live at higher elevations than the subspecies of the Polyglottus group. They are thought to be the descendants of a first wave of sedge wrens that left North America and moved down to South America .

The 6 subspecies in the Platensis group are :

• C. p. aequatorialis

• C. p. graminicola

• C. p. tucumanus

• C. p. platensis

• C. p. hornensis

• C. p. falklandicus

Polyglottus group
There are 3 subspecies in the Polyglottus group which are also found in South America. They range from Columbia to Venezuela and there are some local populations in southeastern Peru, northern Bolivia and southeastern Brazil. The subspecies in this group are thought to be the descendants of the second wave of sedge wren invading from the North .

The 3 subspecies in this group are : • C. p. polyglottus

• C. p. alticola

• C. p. minimus

Distribution
In North America, they can be found during the breeding season in the southern half of Alberta and Saskatchewan and in southern Ontario and Quebec in Canada and in the United States, West of the Appalachians, from the Canadian border down to Missouri and northern Arkansas. During migration and winter they are found from the southern half of Arkansas down to Texas and Florida.

In Central America, they reside in the northeastern part of Mexico during winter. They are also year-long residents in central Mexico down to Costa Rica

In South America, they are found all year in Argentina, Venezuela, Equator Peru, Chile, Bolivia, Brazil, Argentina and the Falkland Islands.

They occur as local populations throughout their range.

Habitat
During the breeding season, sedge wrens generally occupy meadows and wet grasslands. They can however live in wetter areas such as marshes and dryer habitat such as dry prairies. They prefer areas with dense and tall grasses and sedges to build their nests.

During winter, migratory sedge wrens can be found in a variety of habitat as long as there is a sufficient abundance of insects to eat. For example, they can be found in pine savannas, dry prairies , meadows , marshes and bogs.

Vocalizations
Songs usually last 1.5 to 2 seconds and start with 3 to 4 high notes or staccato chips followed by a series of thrills. While both male and females can produce calls, only the males sing. Males sing from late winter to early spring on non-breeding grounds and throughout the breeding season to attract mates. They sing both during the day and the night. While males usually sing to attract females, they can also engage in countersinging, where a male will respond to another male's song. A male will usually answer the other male with a different song type and frequently change song types during the interaction. Both males also usually sing faster during countersinging. It is hypothesized that they do so to send the maximum amount of stimuli to the listener whether it be a male, a male or a potential mate.

Improvisation
North American sedge wrens improvise their songs rather than learning them from other birds. Lab and field observations demonstrated that males had large ranges of individually unique songs and that their songs were poor imitations of the same template songs. There was also very little song sharing among males. This large variation results from the tendency of North American sedge wrens to move often. North American sedge wrens are nomadic breeders compared to their sedentary central and South American relatives. They breed where moist meadows and grasslands are available and they may not return to the same locations the next year if conditions are not right. Furthermore, adult birds may switch locations after raising their first brood to go to wetter areas. There is thus a lot of movement and mixing of populations and birds rarely have the same neighbor twice. Therefore, there is no selection for a precise imitation of the neighboring birds and variations arise in the males' songs. Moreover, because their songs vary so much naturally, it decreases the overall variation over large geographic scales and wrens from all over North America can communicate with each other regardless of which population they came from. Conversely, central and South American sedge wrens are sedentary and learn their songs by imitation rather than improvising them.

Diet
Sedge wren forage on the ground for insects and spiders. They eat many types of insects such as moths, flies and grasshoppers.

Migration
Only the North American subspecies of sedge wren migrate. Sedge wrens are short-distance and nocturnal migrants. They leave their wintering grounds between early April and mid-May and usually arrive at their breeding grounds between mid-April and mid-May. They will typically leave their breeding grounds when frost reduces significantly the abundance of insects. They depart anywhere from August in the northern part of their range to the end of October in the central states to arrive in their wintering grounds starting in early September.

Dual breeding migration
There is some evidence that some sedge wrens may go through a second migration during the breeding season to breed at a second location. Sedge wrens were observed arriving and breeding from mid to late summer in the Central Plains of the United States and in Iowa where they were previously absent in early summer. It is however not actually known if these birds bred somewhere else before. There are several hypotheses to explain this potential second migration. One hypothesis is that these birds are coming from the northern part of their range where shorter summers prevents them from having a second brood in the same location. Another similar hypothesis is that these birds come from various locations where the environmental conditions changed and were no longer suitable for raising a second brood. A final hypothesis is that males that were not able to breed at their previous location relocate to the central plains. They will then wait for the arrival of females that are relocating and try to breed with them.

Reproduction
Some males are polygynous while others are monogamous. Polygynous males are usually more successful than monogamous males because breeding with multiple females increases their number of offsprings. Males arrive earlier than females at breeding sites to establish territories and the ones defending territories with more nesting sites and food usually attract more females. Males are also the ones building the nests. They build multiple nests which serve for nesting, as dormitories and as decoys for predators. The females will then add a lining of grass, sedge and feathers to the nest she chooses. Nests are round globes of dried grass with a round opening on the side. They are usually built in grasses and sedges about one or two feet above ground or shallow water. Females usually lay 7 eggs but it can vary from 1 to 10 eggs eggs which she incubates for 12-16 days   .The eggs are oval shaped with no markings and measure on average 16 by 12 mm. The young hatchlings are altricial. The females do most of the parental care and feeding whilst the males continue to build nests and display for other females. However, males will also occasionally feed the young. The young leave the nest after 11-16 days. Some early breeding females can also have a second brood later in the season.