Breeding Habitat:Grassland
Nest Type:Open-cup nesting passerine
Migration Status:Short distance migrant
Nest Location:Ground-low nesting
Breeding Savannah Sparrows occupy a wide range of habitats, from alpine tundra and bogs to coastal dunes, but throughout most of their range, they are normally associated with grasslands. Their preferred habitats consist of patches of bare ground or short vegetation interspersed among taller dense grasses (Wiens 1973), habitats that may be found in pastures, hayfields, native prairies, the grassy edges of marshes, and reclaimed strip mines (Brewer et al. 1991, Brauning 1992). In western North America, they also inhabit montane meadows (Andrews and Righter 1992).
Savannah Sparrows are one of very few grassland birds to noticeably expand their breeding range during the twentieth century. This expansion is most noticeable in the Great Lakes region, where the breeding range has spread southward from the upper Great Lakes to the vicinity of the Ohio River (Brewer et al. 1991, Peterjohn and Rice 1991). Its breeding range is still expanding in Kentucky (Monroe et al. 1988). Similar expansions have not been apparent elsewhere in its range, which has remained fairly stable in recent decades. Along BBS routes, this species is numerous across southern Canada and the northern U.S., except for the Pacific northwest (Relative Abundance Map). A few records along the southern boundary of the range shown on this map may pertain to late migrants or nonbreeders.
As is true for most grassland birds, Savannah Sparrow populations have generally declined since the mid-1960s. During 1966-1994, significant declines occur in 9 states/provinces, 10 physiographic strata, the Eastern BBS Region, U.S., and survey-wide (Trend List). In contrast, increases are limited to 4 states/provinces, one stratum, and the Western BBS Region. Similar trends are evident during the 1966-1979 and 1980-1994 intervals, with decreases outnumbering increases within the states/provinces and strata. The regional trends present a more varied pattern, with increases in the Western BBS Region during 1966-1979, declines in the Eastern BBS Region after 1980, and stable trends in the Central BBS Region during both intervals. The trend maps also shows varied geographic patterns to the population trends. Declines are most prevalent from Ontario, Minnesota, and Iowa eastward (Trend Map). A mosaic of increases and decreases are evident elsewhere, with increases most prevalent along the northern Rocky Mountains and adjacent Great Plains.
The survey-wide indices are fairly stable through 1978, but show an abrupt decline through 1980 followed by stable trends (Survey-wide Annual Indices). While trends in the Eastern BBS Region are similar, trends in the Central BBS Region have remained fairly stable throughout the survey period and those in the Western BBS Region have shown a slight increasing tendency (Central BBS Region Annual Indices) (Western BBS Region Annual Indices). A variety of temporal patterns are exhibited by the populations in states/provinces and strata. In eastern North America, Savannah Sparrow populations have generally declined since the mid-1960s, as exemplified by the trends in Pennsylvania, New Brunswick, and the Great Lakes Plain (S16) stratum (Pennsylvania Annual Indices) (New Brunswick Annual Indices) (Great Lakes Plain Annual Indices). In Wisconsin and Nova Scotia, declines are most apparent during 1975-1980 (Nova Scotia Annual Indices) (Wisconsin Annual Indices). The North Dakota population declined through the late 1970s, followed by fairly stable trends (North Dakota Annual Indices). In the Great Lakes Transition (S20) stratum, the population increased through 1977, followed by a decline through 1982 and then fairly stable trends (Great Lakes Transition Annual Indices). Where Savannah Sparrows have increased, such as Alberta, these trends are most apparent prior to 1980 (Alberta Annual Indices). In the Aspen Parklands (S30) stratum, however, increases are most apparent beginning in the late 1980s (Aspen Parklands Annual Indices).
During the winter months, Savannah Sparrows are numerous residents across the southern U.S. from California to the Carolinas, with small numbers wintering farther north. This winter range is primarily south of the regions affected by the severe winter weather of the mid-1970s, and no marked declines were apparent during those years. Population trends on CBCs are mixed increases and declines, although most significant trends are in a negative direction.
In the northeastern U.S., reforestation has eliminated many suitable habitats and is the primary factor responsible for recent population declines (Laughlin and Kibbe 1985). Habitat loss is probably responsible for declines elsewhere, primarily the conversion of grasslands to cultivated fields or other unsuitable habitats (Andrews and Righter 1992, Peterjohn and Rice 1991). The more frequent mowing of hayfields may also be a factor, as breeding pairs may not have sufficient time between mowings to successfully raise a brood.
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Natur. Hist., Denver, CO. 442 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.
Laughlin, S.B., and D.P. Kibbe, eds. 1985. The atlas of breeding
birds of Vermont. Univ. Press of New England, Hanover, NH.
456 pp.
Peterjohn, B.G., and D.L. Rice. 1991. The Ohio breeding bird
atlas. Ohio Dept. Natur. Resour., Columbus, OH. 416 pp.
Wiens, J.A. 1973. Interterritorial habitat variation in
Grasshopper and Savannah sparrows. Ecology 54:877-884.