Field Sparrow Habitat Model
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Draft Date:
May 2001

Species:
Field sparrow, Spizella pusilla

Use of Study Area Resources:
Reproduction and wintering; occurs throughout most of the eastern half of North America (Carey et al. 1994).  Within the study area the range includes Massachusetts, New Hampshire, and the southern half of Maine.

Habitat Requirements:
Cover: Field sparrows nest in brushy fields, forest edges, woodland openings, roadsides, open shrublands, early successional forests, and occasionally orchards, tree farms, or nurseries (Carey et al. 1994, Dechant et al. 2001, DeGraaf and Rappole 1995).  Nesting habitat offers a combination of abundant herbaceous vegetation and shrubs or other low, woody perches (Sousa 1983). Field sparrows were described as an edge species by Johnstone (1947 in Dechant et al. 2001) who noted that they stayed "within or near the forest edge, not venturing deeper than a few meters into the forest, nor farther than 12-15 m into surrounding fields".  Sousa (1983) described optimal habitat as early successional, with 50-70% shrub cover and 50-90% grassy herbaceous cover. Optimal shrub heights were < 1.5 m, and optimal herbaceous cover height was 16-32 cm during nesting, although taller vegetation were also used (Sousa 1983). Vickery (1993) found that field sparrows used burned or herbicide treated grasslands in Maine only after a period of vegetational succession.

Nests are built on the ground early in the season when groundcover is low, and are built higher off the ground or in low shrubs as the season progresses (Carey et al. 1994). Their nests are parasitized by brown-headed cowbirds, to which they often respond by abandonment and renesting (Carey et al. 1994).

They are tolerant of urban sites (R. Boone), but do not breed near human habitation (Carey et al. 1994).

Vickery et al. (1994) observed only limited statistical correlation between habitat area and use, but Sousa (1983) proposed a minimum habitat area of 2 ha.

Winter habitats include grazed pastures, and agricultural fields in addition to the open grassy and brushy habitats used for nesting (Allaire and Fisher 1975 in Carey et al. 1994).

Forage: Field sparrows eat a combination of insects and seeds, varying with availability and seasonality. The young are fed spiders and a variety of insects including arthropods, caterpillars, grasshoppers, crickets, spiders, flies, bees, katydids, cicadas, and moths. Winter forage includes more small seeds and grains. (Carey et al. 1994).

Model:
The Breeding Bird Atlas and Breeding Bird Survey data for Maine, New Hampshire and Massachusetts (courtesy of the University of Vermont COOP Unit) were used to identify the range of the field sparrow within the study area. The range was delineated by including all USDA Forest Service Ecological subunits (Keys et al. 1995) in which sparrows were know to occur. Habitat mapping then was restricted to these areas. Field sparrow habitats were identified by selecting suitable cover types (see table, below).

The grassland class in our land cover theme included not only late successional brushy grasslands, suitable for field sparrows, but also highly managed areas such as golf courses, lawns, parks and hayfields.  Because of the range of conditions aggregated in this class, we assigned it a moderate (0.5) habitat suitability score, providing it was adjacent (within 60 m) to upland shrub cover.  Shrub cover within 60 m of grasslands was assigned  an intermediate (0.8) score. The highest score (1.0) was applied only to grass and shrub cover types at locations 1) managed so as to cycle through appropriate an successional stage (e.g., powerline corridors), or 2) areas known to be used by other grassland birds (e.g., areas having sightings of 2 or more grassland bird species or 3 or more individual grassland birds, from Shriver et al. 1999).  Fringes of such grasslands are likely to be or become suitable for field sparrows. Finally, we retained only grassland/shrub complexes 2 ha or larger in area.

Model testing: The field sparrow occurrences along Breeding Bird Survey routes throughout the study area were used to test the habitat map. We compared the presence of habitat near a random set of 618 upland points within the range of the bird, to that for Breeding Bird Survey stops at which field sparrows were observed in 1990, 1997, or 1998. Of the 35 sites with birds, 29 had mapped habitat, while only 289 sites out of the 618 randomly distributed sites had habitat. The Chi-square was highly significant, indicating that the overall model does indicate localities useful to field sparrows. Moreover, the level of significance was higher when testing just the highest suitability level (1.0), indicating that the relative assignment of scores is valid. Distribution also was checked against Pierce and Melvin (1991) surveys of major grassland habitats.

Sources:
Boone, R. Maine Gap Analysis, Maine Cooperative Fish and Wildlife Research Unit; WWW page http://www.wle.umaine.edu/progs/unit/gap/

Carey, M., D.E. Burhans and D.A. Nelson. 1994. Field Sparrow, Spizella pusilla. In A. Poole and F. Gill, (eds.) The Birds of North America, No. 103. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, Washington, D.C.

DeGraaf, R.M. and J.H. Rappole. 1995. Neotropical Migratory Birds: Natural History, Distribution and Population Change. Comstock Publishing Associates, Ithaca, NY. 1995. 676 pp.

Dechant, J.A., M.L. Sondreal, D.H. Johnson, L.D. Igl, C.M. Goldade, B.D. Parkin and B.R. Euliss. 1999 (revised 2001). Effects of management practices on grassland birds: Field Sparrow. Northern Prairie Wildlife Research Center, Jamestown, ND. 20 pages.

Keys, J.E., Jr., J.C. Carpenter, S. Hooks, F. Koenig, W.H. McNab, W. Russell and W. Smith. 1995. Ecological units of the eastern United States - first approximation (map and booklet of map unit tables), USDA Forest Service. Atlanta, GA.

Pierce, S.P. and S.M. Melvin. 1991. Assessment of barrens/grassland birds and habitats in Maine. Report to Maine Department of Inland Fisheries and Wildlife, Augusta, ME. 14 pp.

Shriver, W.G., R.J. MacCulloch, and J.V. Wells. 1999. Grassland Birds Data Compilation Project for the Northeast U.S. (USFWS Region 5). USFWS, Hadley, MA.

Sousa, P.J. 1983. Habitat Suitability Index Model: field sparrow. FWS/OBS-82/10.62.

Vickery, P.D. 1993. Habitat selection of grassland birds in Maine. Ph.D. dissertation, Univ. of Maine, Orono, ME. 124 p.

Vickery, P.D., M.L. Hunter, Jr. and S.M. Melvin. 1994. Effects of habitat area on the distribution of grassland birds in Maine. Conservation Biologist 8(4):1087-1097.