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Henslow's Sparrow: Summary of June 1996 Status Assessment
Prior to European settlement, Henslow's sparrow (Ammodramus henslowii) bred primarily in prairie habitat. With the loss of native prairie to agriculture, the Henslow's sparrow adapted to breeding in secondary grassland habitats, particularly hayfields and pasture. The availability of these secondary habitats also allowed the species' range to expand to the north and the east as forests were cleared for agriculture. The species currently breeds locally across the Great Lakes region of the eastern United States and southern Ontario (Canada), to New York, south to Maryland, across northern Virginia, West Virginia and Kentucky, and west to eastern portions of Oklahoma and Kansas. The breeding range, particularly in the northwestern and eastern portion of the range, is contracting. The species winters in coastal areas from South Carolina, south to Florida, and west to Texas.
Grasslands which provide Henslow's sparrow breeding habitat are characterized by tall, dense grass with a well-developed litter layer and a relatively high coverage of standing dead vegetation. The grasslands support sparse woody vegetation, but extensive woody invasion preclude use by Henslow's sparrow. Habitat area is considered a limiting factor for Henslow's sparrow; only large grasslands support persistent populations.
Winter habitats of Henslow's sparrow are similar to breeding habitats, in that they are dominated by dense groundcover. Either pine forests or open prairies are suitable winter habitat, provided that dense groundcover is present. The winter habitat requirements have not been rigorously studied until recently; 3 ongoing studies represent the first systematic research on wintering Henslow's sparrows.
The scientific community has expressed concern regarding Henslow's sparrow populations for decades, but it has been difficult to document population trends. North American Breeding Bird Survey (BBS) data clearly indicate a significant population decline for this species (since 1966) which is fairly consistent throughout its breeding range. Christmas Bird Count data indicate that the species' population is also declining on winter range. The distribution of Henslow's sparrow is scattered and localized throughout its current range. In 1987, the U.S. Fish and Wildlife Service identified Henslow's sparrow as one of 30 "migratory nongame birds of management concern in the United States" due to the species' widespread population decline and need for restricted/vulnerable habitats. The Henslow's sparrow is listed as endangered, threatened, or a species of special concern in 16 states and was designated as endangered in Canada in 1993. This status assessment includes summaries of the status of Henslow's sparrow in 38 states and Canada, which make up the current and historic range of the species.
Loss and deteriorating quality of grassland habitats is an underlying cause for Henslow's sparrow population declines. The area of native prairie in North America, which historically provided prime Henslow's sparrow breeding habitat, has declined dramatically; some estimates are as high as 99.9%. The availability and quality of secondary agricultural habitat have also declined. Much agricultural land has been lost to development or reverted to forest. In addition, many hayfields and pastures have been converted to row crop production. Disturbances in remaining hayfields have intensified with trends toward earlier and more frequent mowing. There have been large-scale losses of grassland habitats in the winter range of the species, as well as the breeding range. Fire-dependent savannas and prairies of the southeast have been destroyed and continue to be threatened by: exclusion or reduction of frequency of fire; drainage; urbanization; and conversion to agriculture or pine plantation. Not only has the overall quantity of habitat declined, but also the average patch size of remaining grassland habitats has declined. The highly fragmented nature of the remaining grassland habitats has serious implications for area-sensitive species such as Henslow's sparrow.
The future of grassland habitats is uncertain. The grassland habitats required by Henslow's sparrow are transitory in nature and require cyclic disturbance (natural or man-made) to be maintained. Publicly-owned lands, lands owned by private conservation organizations, and possibly lands enrolled in the Conservation Reserve Program (CRP) offer the most potential for Henslow's sparrow management. There is a need to evaluate the potential for improving grassland management practices, particularly on publicly owned lands which currently support most large, persistent populations of Henslow's sparrow. Opportunities to incorporate grassland bird management into agricultural programs, particularly the CRP, and innovative agricultural practices, such as rotational grazing, should also be evaluated.
Cyclic disturbances are necessary to maintain grasslands, and consequently grassland bird populations. Prescribed burning, mowing (haying), and grazing are three management tools which have been successfully applied to maintain Henslow's sparrow breeding habitat. On winter range, protection and maintenance, through fire, of natural pinelands is imperative. Mowing and/or grazing may be effective management tools for potential secondary wintering habitats, such as broomsedge fields and powerline corridors. However, the ability of these habitats to support viable wintering populations of Henslow's sparrow has yet to be determined. The timing, extent and frequency of disturbance are important considerations in managing both breeding and wintering habitat. Management plans must also address the size of the management area.
Any effort to manage for Henslow's sparrow should not be viewed in isolation, but rather should be seen as an opportunity to benefit a wide-range of species associated with grassland habitats. The grassland ecosystems on which Henslow's sparrow depends are considered among the most endangered ecosystems in North America. Integrated management for grassland-dependent species is a sound ecological approach, and also makes most efficient use of economic and logistic resources. Recent initiatives demonstrate that conservation and management of grassland birds are receiving increased attention; these initiatives need to be encouraged and expanded.
Henslow's sparrow research priorities include: 1) monitoring the status of the largest, persistent breeding populations, 2) documenting additional breeding populations, 3) systematically surveying suitable habitat on the winter range to identify key wintering areas, and 4)evaluating habitat requirements and ecology of the species in winter range.
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