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Species of Concern
Region 3 Decision on the Status Recommendation for Henslow's Sparrow
Region 3 of the U.S. Fish and Wildlife Service (Service) has decided to retain the Henslow's sparrow as a "Species of Concern," and will not make it a Candidate Species for Federal listing as threatened or endangered at this time. The Service believes the Henslow's sparrow currently borders on qualifying for Candidate Species status, but there is insufficient evidence that the species should become a Candidate Species at this time. Existing population trend data are not sufficiently precise to indicate the rate of the decline, and there are six breeding range states where the species' population trends are unknown. Furthermore, there are several large populations in which the species appears to be doing well. Service biologists and partners will continue to collect and review data on the status of the Henslow's sparrow, and the Service may determine at any time that the species warrants elevation to Candidate status if the data so indicate. The Service recommends increased population monitoring of the species throughout its range, especially at the locations of the larger populations and in Indiana, Kansas, and Missouri (key states where the population trend is unknown). The Service encourages owners and managers of grasslands to strive to maintain large blocks of unfragmented grassland habitat having the proper vegetative components necessary to the Henslow's sparrow for its long-term survival. The species needs active grassland management - burning, haying, light grazing, and planting - in order to create and maintain tall and dense grasses and forbs with a well-developed litter layer and sparse woody vegetation.
The U.S. Fish and Wildlife Service's Bloomington, Indiana, Ecological Services Field Office has the lead responsibility for determining whether the Henslow's sparrow (Ammodramus henslowii) should be proposed for listing as a threatened or endangered species. The Bloomington Field Office reviewed published and unpublished data for the Henslow's sparrow over its entire range. Furthermore, that office prepared a detailed range wide status assessment report on the species (Pruitt, Lori. 1996. Henslow's Sparrow Status Assessment - June 1996. Unpublished report to Nongame Migratory Bird Coordinator, U.S. Fish and Wildlife Service, Ft. Snelling, MN.) and a summary of the Henslow's Sparrow Status Assessment Report. Based on that review and status report, the Bloomington Field Office recommended that the Henslow's sparrow not be elevated to the status of a Candidate Species, but that it remain as a regional "Species of Concern." The endangered species and migratory bird program staffs in the Region 3 Regional Office support that recommendation. Therefore, Region 3 has determined that the Henslow's sparrow will not be elevated to the status of a Candidate species at this time. The species will be retained as a "Species of Concern" and Region 3 will remain the lead region for ongoing review of its status.
"Species of Concern" is an informal term that refers to those species which Region 3 believes might be in need of concentrated conservation actions. Such conservation actions vary depending on the health of the populations and the types and degree of threats. At one extreme, there may only need to be periodic monitoring of populations and threats to the species and its habitat. At the other extreme, a species may eventually require listing as a Federal threatened or endangered species and become the subject of a Federal recovery program. Species of Concern receive no legal protection under the Endangered Species Act as a result of this informal status, and the use of the term does not necessarily mean that the species will eventually be proposed for listing as a threatened or endangered species. As funding and staffing levels permit, Region 3 evaluates Species of Concern to determine the extent of their conservation needs and to determine whether additional legal protection should be sought for them. (Note: All migratory birds are protected by the Federal Migratory Bird Treaty Act).
The Henslow's sparrow is an especially difficult species to evaluate for possible elevation to candidate species status. It historically ranged across portions of 32 states in the eastern half of the United States and into southern Canada, but within this large area individuals and nesting populations have become scattered and localized. The species is affected by habitat loss and degradation stemming from a variety of causes, and the magnitude of these threats varies greatly across the species' range. It may also be threatened by habitat degradation on its southern U.S. wintering grounds. Although concern over its decline has been expressed for several decades, upon close examination the scientific data on the extent of the decline are inconclusive.
There is clear documentation of massive loss of the species' native prairie habitat, and to a lesser degree there has been a subsequent decline in acreage and suitability of the hayfields and pastures which the species has secondarily occupied. The Henslow's sparrow needs tall and dense grasses and forbs with a well-developed litter layer for nesting habitat; standing dead herbaceous vegetation or sparse short woody vegetation also may be important for song perches. Obviously, the species has undergone a resultant decline in numbers and range, especially in the eastern and northwestern portions of its breeding range.
Breeding Bird Survey (BBS) data provide the best rangewide Henslow's sparrow population trend information, and their estimated 8.2 percent rate of average annual decline in the United States between 1966 and 1994 appears conclusive upon first examination. However, species occupying rare habitats or which are otherwise very locally distributed may not be suitably surveyed by BBS methodology (roadside counts from fixed locations) since they are generally detected at very low relative abundances on relatively small numbers of BBS routes. In addition, the species' secretive nature and its very short, soft vocalizations make Henslow's sparrows especially difficult to survey, and they can be easily overlooked by BBS participants. While BBS data indicate a decline of Henslow's sparrow populations, these trend estimates are relatively imprecise and may not accurately reflect the rate at which the populations are actually changing.
Furthermore, BBS routes do not cover several areas where there are known to be relatively large and stable-to-increasing populations of Henslow's sparrows. Information from these areas suggests the species may be expanding in range and numbers in portions of its historical range, but the BBS is unable to provide any insight into this possibility. Additionally, in Ohio and western Pennsylvania the species colonized grasslands that had been planted on reclaimed strip-mined areas; for the most part, BBS surveys do not sample these areas. More detailed and longer term studies are needed at sites such as these to determine long-term population trends and the factors promoting those trends.
The presettlement range of the Henslow's sparrow will never be known, but it is believed that the creation of suitable grassland habitat in the form of hayfields and pastures allowed the species to expand its breeding range eastward and northward as European settlement of North America progressed and the clearing of forested land accelerated. There is evidence that the species expanded its range and numbers in New England and the Middle Atlantic states in the early 1900's. Thus, the more recent declines and local extirpations of the species in New England and parts of several other eastern and northern states must be viewed cautiously when evaluating the species' status. By themselves these declines are insufficient justification for proposing the species for threatened or endangered status, even though some unique genetic material may be lost if the declines continue.
There are six breeding range states Indiana, Kansas, Kentucky, Missouri, New Jersey, and Virginia where the species' population trends are unknown. Because Indiana, Kansas, and Missouri contain substantial and seemingly stable or increasing Henslow's sparrow populations, better data on trends in most of these states should be obtained before the Service makes a decision on the species' status.
Grasslands created by enrolling former croplands in the Conservation Reserve Program appear to be important, or to have potential importance, to Henslow's sparrow populations in several states. Because of the uncertain long-term security of these areas (beyond the 10-year CRP lease), it remains to be seen if they will stabilize the species' population at more than a local scale.
Christmas Bird Count (CBC) data are the only population trend data available for wintering Henslow's sparrows, but CBC data are not suitable for statistical analysis. In these counts there is no requirement for year-to-year consistency in numbers or experience of observers, intensity of effort, or the amount of the count area that is covered. For the three states where rudimentary trend estimates can be made, Texas showed a 1963-87 average annual decline of 2.2 percent and Florida a decline of 2.5 percent annually, while Louisiana had a stable winter population over that period.
In conclusion, while there is clear evidence of a decline in range and numbers of the Henslow's sparrow in the eastern and northwestern corners of its range, it is unclear whether this decline has taken the species across thethreshold of endangerment, i.e., "in danger of extinction throughout all or a significant portion of its range" or threatened status, i.e., "likely to become an endangered species throughout all or a significant portion of it range." The apparent stability and expansion of two large western populations (Kansas and Oklahoma) and the apparent stability or large size of two Midwestern populations (southwestern Missouri, southern Indiana) suggest the species is faring better than previously believed in some areas. The inconclusive data, and especially the need for additional population trend data from the six breeding range states where the population trend is unknown, put the Henslow's sparrow somewhere in the gray area between "well justified for listing" as threatened or endangered and "clearly not in need of listing."
The USGS Migratory Bird Research website provides additional information on the Henslow's sparrow.
Status Assessment Prepared July 31, 1997