Avian habitat can be divided into three primary types: nesting cover, brood-rearing cover, and roosting cover. The ideal characteristics of these cover types vary dramatically based on primary use and with avian species. Ground-nesting species typically prefer nesting cover that is 15 to 43 cm tall and composed primarily of dead material from the previous growing season. Both warm- and cool-season bunchgrasses can provide this type of cover (Clubine, 1995). Brood-rearing cover requires a mix of bare ground for dusting and a high proportion of forbs where chicks and mothers can forage for insects, seeds, and green material. Dense, close-growing grasses are less desirable for brood cover because the matted vegetation hinders movement. Roosting locations can range from tall-growing grasses to dense erect forbs and low-growing shrubs. Birds will often use unmown grasses as roost cover early in the season, but as temperatures drop in winter they will move to the denser cover of shrub thickets (Clubine, 1995).
Extensive studies of bird behavior and species diversity in British Columbia determined that visually obvious vegetation features were sufficient to describe breeding bird-habitat relationships (Schwab et al., 2006). They also concluded that maximum avian species diversity is obtained when a variety of successional stages of vegetation is present. Grasshopper sparrows (Ammodramus savannarum) are a widely adapted grassland bird species. Evaluation of habitat characteristics preferred by grasshopper sparrows indicated that these birds preferred open grasslands with grass basal cover of 26% and bare ground of 22% (Whitmore, 1981). Open areas allow free movement of ground-feeding birds among grass clumps, while grass clumps provide nesting cover.
Bobwhite quail (Colinus viginianus) typically prefer habitat that consists of 50% open exposed ground and 50% a mix of upright woody and herbaceous vegetation. Optimal nesting habitat is considered 40 to 60% bare ground (Schroeder, 1985). Diets of the majority of quail and many other ground-feeding birds consist of seeds and insects. During the spring and summer much of the diet consists of insects, while small seeds comprise the majority of the diet when they are available. As seed availability decreases through the winter, the food supply can become limiting until early-maturing weeds start to drop seeds in mid- to late spring (Rosene, 1969). Quail require either completely bare ground or light litter cover to access these seeds. One of the major problems with tall fescue as bobwhite habitat is the development of a thick sod mat where the birds are unable to scratch for seeds (Barnes et al., 1995).
It is possible that tall fescue can be managed to improve its suitability as bobwhite habitat. Bobwhite nesting usually occurs in nearly bare ground with stems far enough apart to allow birds to walk through easily. Bobwhites rely on residual vegetation from the previous year for nest building. Ideal roosting cover varies with the season, with thicker brush preferred in the winter to reduce wind chill (Klimstra and Ziccardi, 1963). In Kentucky, management treatments designed to disturb the tall fescue canopy and create bare ground have improved the habitat for winter feeding, roosting, and nesting (Table 28-3, Fig. 28-3) (Barnes et al., 1995; Madison et al., 2001). Disking created a more open canopy with greater vegetative diversity later in the season than immediately following disking. Application of glyphosate [N-(phosphonomethyl)glycine] herbicide also opened the tall fescue canopy and improved its usefulness as bobwhite habitat.
Burger et al. (1990) similarly found that most CRP lands seeded to tall fescue were unsuitable for quail habitat in the first 3 yr after establishment if not disturbed. Improvement of tall fescue as bobwhite roosting habitat also may be accomplished through grazing management to open the canopy and create clumps. Grazing with sufficient pressure will create bare ground and reduce litter density, allowing birds to have access to seeds and the soil surface.
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Table 28-3. Characteristics of acceptable bobwhite quail cover and tall fescue pasture treated with various management practices (adapted from Rosene, 1969; Schroeder, 1985; Klimstra and Ziccardi, 1963; Madison et al., 2001).
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Fig. 28-3. Impact of grazing by beef cattle and goats on tall fescue structural characteristics (photo by Gregory L. Brann, USDA-NRCS, with permission).
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