Corruíra-do-campo (Cistothorus platensis). Formerly the Short-billed Marsh Wren, this species was renamed Sedge Wren to better distinguish it from the closely related Marsh Wren (Cistothorus palustris) by emphasizing habitat differences between the two species. The Sedge Wren is a broadly distributed, polygynous species, with many disjunct populations occurring in North, Central, and South America. The Sedge Wren appears to be one of the most nomadic terrestrial birds in North America, with breeding concentrated in widely different portions of its range at different times of the breeding season. A first period of nesting is concentrated primarily in the upper-midwestern United States (Wisconsin, Minnesota, North Dakota) and adjacent Canada (Saskatchewan) and occurs during late May and June. A second, more widespread, nesting period occurs later in the summer (July¿September), with birds expanding out into southern (for example, Nebraska, Kansas, Missouri) and northeastern (for example, Vermont, Massachusetts) portions of the breeding range. Sedge Wren habitats are characterized by vegetation and soils that are highly susceptible to drying or flooding caused by annual and seasonal variation in rainfall. Vegetative succession or disturbance caused by grazing, haying, and planting also impart a highly transitory character to Sedge Wren nesting habitats. This habitat instability apparently has led to high mobility and low site tenacity in many areas. The Sedge Wren's communication system also appears to be adapted to high population mobility, suggesting that opportunistic breeding has occurred for a long time rather than being of recent origin, such as in response to recent agricultural changes or habitat loss.
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