Nest Type:Open-cup nesting passerine
Migration Status:Short distance migrant
Nest Location:Ground-low nesting
The enigmatic Henslow's Sparrow is another inconspicuous occupant of grassland habitats in eastern and central North America. With its furtive habits and plain song, this species is easily overlooked. Only sketchy information is available on its historic status and distribution. Its original breeding range may have consisted of tall grass prairies in the midwest and various grassland habitats along the mid-Atlantic coastal plain (Hyde 1939). Deforestation allowed it to expand its breeding range in the Great Lakes region, primarily during the first half of the twentieth century. After 1950, its populations have been declining through most of its range (Andrle and Carroll 1988, Brewer et al. 1991, Cadman et al. 1987). However, reclaimed strip mines provide suitable habitats for this species, and the bulk of its remaining populations occupy these habitats in eastern Ohio and western Pennsylvania (Brauning 1992, Peterjohn and Rice 1991).
Breeding Henslow's Sparrows have always been locally distributed, frequently forming loose "colonies" (Hyde 1939). This local distribution, combined with its inconspicuous behavior, cause this species to be poorly represented along most BBS routes. It is recorded in small numbers throughout its current range (Relative Abundance Map). All trend estimates during 1966-1994 are in a negative direction, including significant declines in 2 states, 3 physiographic strata, the Eastern BBS Region, U.S., and survey-wide (Trend List). Similar trends are evident during both the 1966-1979 and 1980-1994 intervals. Declines predominate throughout most of its range (Trend Map). However, local increases in southeastern Ohio may correspond to the creation of habitats on reclaimed strip mines since 1970. The survey-wide indices exhibit a constant decline since the mid-1960s (Survey-wide Annual Indices). Similar temporal patterns are indicated for most states/provinces and strata.
During the breeding season, Henslow's Sparrows have very specific habitat requirements. They are mostly found in fallow fields supporting tall, dense grassy and weedy cover with a high density of standing dead vegetation as well as scattered bushes or very small trees (Zimmerman 1988). In some portions of their range, breeding pairs prefer damp habitats although they are regularly found on dry hilltops in other areas (Andrle and Carroll 1988, Brewer et al. 1991). Habitat loss is thought to be largely responsible for population declines since 1950. Successional changes producing unsuitable habitats, the conversion of native grasslands to cultivated crops, and drainage of wetlands have all contributed to the decline and disappearance of some populations (Andrle and Carroll 1988, Cadman et al. 1987).
When not singing, Henslow's Sparrows skulk through the grassy vegetation and are infrequently encountered. Hence, little information is available on their status away from the breeding grounds. They are observed in small numbers on CBCs, primarily in the southeastern states west to eastern Texas. These limited data also suggest that the populations are generally decreasing, but should be viewed with some caution since this species is under- represented on CBCs throughout its range.
Andrle, R.F., and J.R. Carroll, eds. 1988. The atlas of breeding birds in New York State. Cornell Univ. Press, Ithaca, NY. 551 pp. Brauning, D.W., ed. 1992. Atlas of breeding birds in Pennsylvania. Univ. of Pittsburgh Press, Pittsburgh, PA. 484 pp. Brewer, R., G.A. McPeek, and R.J. Adams, Jr., eds. 1991. The atlas of breeding birds of Michigan. Michigan State Univ. Press, East Lansing, MI. 594 pp. Cadman, M.D., P.F.J. Eagles, and F.M. Helleiner, eds. 1987. Atlas of the breeding birds of Ontario. Univ. of Waterloo Press, Waterloo, ON. 617 pp. Hyde, A.S. 1939. The life history of Henslow's Sparrow, Passerherbulus henslowii (Audubon). Univ. Mich. Mus. Zool. Misc. Publ. No. 41. 72 pp. Peterjohn, B.G., and D.L. Rice. 1991. The Ohio breeding bird atlas. Ohio Dept. Natur. Resour., Columbus, OH. 416 pp. Zimmerman, J.L. 1988. Breeding season habitat selection by the Henslow's Sparrow (Ammodramus henslowii) in Kansas. Wilson Bull. 100:17-24.