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Effects of Fire on Bird Populations in Mixed-grass Prairie

A Proposed Conservation Strategy


Results presented here suggest a conservation strategy for the northern Great Plains involving prescribed burning. On large areas, such as wildlife refuges, only portions should be burned in any particular year, and these on a rotational basis. The same prescription would apply to smaller areas that can be considered as components in a landscape, such as waterfowl production areas. They should be burned periodically, but not all in the same year. That strategy will assure that in any given year habitats in a variety of successional stages will be available for a variety of breeding bird species.

This prescription will provide habitat for birds in two of the three categories, although those that benefit from long-term protection from fire will suffer. True grassland species should be emphasized in the management of mixed-grass prairies. Birds that favor short and sparse vegetative cover are common and widespread, or have positive or neutral population trends, as indicated by Breeding Bird Survey results (Table 2). Also, many of these birds use habitats such as cultivated fields and heavily grazed pastures, which are made available from agricultural operations (Best et al. 1995), although the reproductive success in such habitats may be inadequate. Further, a regime of prescribed fires will provide suitable habitat for these species immediately following each fire.


Table 2. Trends from Breeding Bird Survey for Central Region, 1966-94 and 1980-94, and route averages for 1966-94.
 
1966-94
1980-94
Species
Route average
Trenda
Trend
Killdeer 8.88 -0.3 -2.0
Marbled Godwit 1.36 0.7 NA
Upland Sandpiper 3.92 2.1 0.3
Willet 1.03 -1.8 -0.4
Eastern Kingbird 7.78 0.2 0.4
Sedge Wren 1.25 1.3 5.7
Yellow Warbler 2.29 -0.2 2.7
Common Yellowthroat 6.87 -0.9 -2.1
Bobolink 6.46 -2.4 -3.0
Western Meadowlark 95.69 -0.3 0.3
Red-winged Blackbird 85.09 -0.5 -1.3
Brown-headed Cowbird 26.17 -0.5 -0.2
Savannah Sparrow 6.98 0.5 1.5
Grasshopper Sparrow 8.95 -2.9 -1.8
Baird's Sparrow 1.82 -0.9 -0.5
Clay-colored Sparrow 6.67 -1.1 0.9
a Average annual change; increasing at P=0.01, increasing at P<0.05, increasing at P<0.10; decreasing at P=0.01, decreasing at P<0.05, decreasing at P<0.10.


Most of the species that favor woody vegetation also are common and widespread and have had neutral or positive population trends (Table 2). They can also rely on habitats provided on private land, including shelterbelts, suburban areas, and wetlands. Moreover, all these species have widespread distributions and are more common elsewhere than the mixed-grass prairies (Price et al. 1995). An exception is the Clay-colored Sparrow. That species has declined during the past 25 years or so, although not significantly, and its center of abundance is in the mixed-grass prairie. A prescribed-burning program that eliminated brushy vegetation would reduce breeding populations of Clay-colored Sparrows. Mitigating this concern is the fact that the species uses brushy habitat, which is common in private pastures, and retired cropland, such as offered by the Conservation Reserve Program (Johnson and Schwartz 1993).

Although true grassland birds suffer short-term habitat losses from a burn, they do require grassland, which in turn requires periodic fire for maintenance. Several of these species have suffered long-term population declines (Table 2). Moreover, they typically do not attain high densities or reproduce successfully in habitats other than grassland, as do birds in the other two categories. Furthermore, these species generally have breeding distributions centered in the grasslands of the midcontinent.

Concern about declining bird populations is widespread (Terborgh 1989), but grassland specialists seem particularly threatened. Numbers of many such species have suffered population declines, as judged by results of the Breeding Bird Survey (BBS), more consistently and severely than other groups of species (Peterjohn and Sauer 1993). More troubling, the BBS was begun in the mid 1960's; we lack quantitative evidence of how grassland birds responded to the massive conversion of native prairie to cropland that took place earlier (Johnson In press).

Further, uncultivated grasslands are vital for certain species. Although some species, such as Horned Lark and Vesper Sparrow, have adapted to cropland habitats (Best et al. 1995), many, such as Sprague's Pipit (Anthus spragueii) and Burrowing Owl (Athene cunicularia), have not. And even those species that use cultivated habitats may not be reproductively successful (Rodenhouse and Best 1983).

The fraction of native mixed-grass prairie that has been protected is small (Samson and Knopf 1994, Noss et al. 1995); most of what remains is privately owned and is used for grazing. Fortunately, much of the publicly owned mixed-grass prairie is included in the National Wildlife Refuge System, either as refuges or as waterfowl production areas. These areas also include many formerly cultivated fields that have been replanted to native or tame grasses and forbs. The areas are managed to benefit wildlife, particularly waterfowl. Also fortunately, a rotational system of prescribed burning, which is necessary to maintain grassland and provide habitat for nesting waterfowl, will provide breeding habitat for many of the terrestrial grassland birds.


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