Written by Bryan Watts
March 3, 2010
Adult Bachman’s Sparrow in hand – Note the large bill, drab brown underparts, and streaked crown. Photo by Bryan Watts.
The Bachman’s sparrow is endemic to southeastern North America and is the only member of the Aimophila genus found within this region. Following a dramatic northerly range expansion in the late 1800s and early 1900s, this species has been contracting back to the core of its historic range in the extreme southeast. Population declines along the northern fringe of the species range have likely been due to secondary succession within abandoned farmland and the increased use of sod-forming grasses. Declines within the core of the breeding range have been due to degradation and loss of the southeastern pine ecosystem and effective fire suppression programs.
Bachman’s sparrow is a disturbance-prone species that occupies a narrow disturbance/successional niche. The species requires pine or open savannas with a high density of grasses and forbs in the first meter layer above the ground and low densities of vegetation in the second to fourth meter layer above the ground. For most locations, habitat maintenance depends on a 3-5 year disturbance interval. In the absence of such disturbance, most habitat patches will become unusable within a short period of time as succession proceeds beyond where it is suitable for the species.
This shows a typical breeding habitat of the Bachman’s sparrow near Charleston, SC. Bachman’s require good ground cover with a sparse mid-story that is characteristic of the historic fire-maintained, southeastern pine ecosystem. Photo by Bryan Watts.
For several decades, Virginia represented the northern range limit for Bachman’s sparrow breeding. First recorded as a breeder in the state in 1897, Bachman’s have been documented in all physiographic areas of the state. Distribution was widespread through the 1960’s reflecting a decades-long wave of secondary succession on abandoned farms. Following the 1960s known distribution was primarily confined to the southeastern Coastal Plain in the heart of the historic pine lands. Exceptions to this were populations that were discovered in the 1990s on bombing ranges with high fire frequencies on 2 military installations.
Map showing the reduction of the Bachman’s sparrow population in Virginia between 1897-1968. Map by the Center for Conservation Biology.
Map showing the reduction to the Bachman’s sparrow population in Virginia between 1869-1999. Map by the Center for Conservation Biology.
During the 1996 breeding season, the Center for Conservation Biology conducted a systematic survey of habitat patches for Bachman’s sparrows in Virginia that covered a 1-degree block or a 5,200 square kilometer area. The study area encompassed all records of the species for the previous 20 years except for those on military lands. This effort included 520 point counts within 280 clear cuts and resulted in the detection of only 6 individuals in 4 patches. Since this effort, the species appears to have disappeared from the state with no recent records, placing the northern range limit in the Carolinas.
Management of the Bachman’s sparrow population in Virginia has been difficult because the species has primarily relied on clearcuts for breeding. Clearcuts are ephemeral habitats that within a landscape context are spatially and temporally dynamic. Simulations in the late 1980s of Bachman’s populations within managed landscapes demonstrated that sustainability is very dependent on the availability of habitats that represent stable sources such as old-growth pine stands that are maintained with regular burning. Unlike clearcuts that may only provide breeding opportunities for short time windows, old-growth stands have the potential to support breeding populations for centuries. These populations may then serve as sources for other maturing forests and clearcuts.
Nest of a Bachman’s Sparrow – Bachman’s often contruct nests within clumps of grass with an entrance hidden by overhanging vegetation. The partially hidden entrance can be seen in the center of the photograph. Photo by Bryan Watts.
Piney Grove Preserve as a nucleus for recovery:
The Piney Grove Preserve is one of the last remnants of old-growth pine in Virginia. The site supports the northernmost population of red-cockaded woodpeckers and since its purchase by The Nature Conservancy has been maintained with an aggressive burning regime. After ten years of intensive management, this site now contains the best quality breeding habitat for Bachman’s sparrows in Virginia. The site now supports three of the four bird species endemic to the southeastern pine ecosystem including the red-cockaded woodpecker, chuck-wills-widow, and brown-headed nuthatch. Despite the ongoing vigil awaiting its return, the remaining species of this exclusive community, the Bachman’s sparrow has yet to colonize the site. Reestablishing a breeding population within Piney Grove may require intervention. Although vigorous populations of Bachman’s do occur within the deep south, potential source populations within the northern Carolinas are also contracting, making the likelihood of natural colonization remote. The translocation of individuals for the purpose of establishing a source population has never been attempted in this species. Piney Grove represents a significant opportunity to explore this management option.
Project sponsored by The Center for Conservation Biology (CCB).
Further reading from CCB:
Watts, B. D. 2000. Bachman’s sparrow management plan: Fort A. P. Hill, Virginia. Center for Conservation Biology Technical Report, CCBTR-00-06. College of William and Mary, Williamsburg, VA. 17pp.
Dunning, J. B. Jr., B. J. Danielson, B. D. Watts and J. Liu. 2000. Studying wildlife at local and landscape scales: Bachman’s sparrows at the Savannah River Site. Studies in Avian Biology. 21:75-80.
Watts, B. D., M. D. Wilson, D. S. Bradshaw, and A. S. Allen. 1998. A survey of Bachman’s sparrows in southeastern Virginia. The Raven 69:9-14.
Dunning, J. B. and B. D. Watts. 1991. Habitat occupancy by Bachman’s sparrow in the Francis Marion National Forest before and after Hurricane Hugo. Auk 108:723-725.
Dunning, J. B. and B. D. Watts. 1990. Habitat occupancy of Bachman’s sparrow: Differences in two habitat landscapes. Auk 107:463-472.