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Effects of Fire in the Northern Great Plains

Effects of Fire on Nongame Birds

Bird species evolving with fire may show fire-adapted behavior and responses, whereas other species exposed infrequently to fire in their evolutionary histories may be severely inhibited by it (Best 1979).

Habitat selection

The selection of breeding habitat by birds is based on the recognition of vegetation structure (foliage patterns and density) which fit preconceived notions of "home." Removal or modification of any vegetation, whether by burning or heavy grazing, reduces the diversity of bird species (Lack 1933).

A spring burn (late April) in shrub-grasslands in Illinois did not cause major changes in field sparrow (Spizella pusilla) territory configurations. There was no male abandonment after the burn. Best (1979) concluded that burning in March or early April may interfere with the process of site selection and ultimately result in reduced population densities because of vegetation structure alterations.

In sagebrush grasslands in Idaho, male sage sparrows expended significantly more time in territorial maintenance after a fall burn than before, while Brewer's sparrows spent about the same amount of time (Winter 1984).

Spring burns in Wyoming in sagebrush-grasslands initially reduced the breeding pair density of green-tailed towhees (Pipilo chlorurus), vesper sparrows (Pooecetes gramineus), and white-crowned sparrows (Zonotrichia leucophrys), but their breeding densities increased 2 years after the burn (McGee 1976).

Breeding pair densities of lark sparrows (Chondestes grammacus) in central Texas were highest in the most recently burned areas (Renwald 1977). They decreased with increased litter buildup and lower grass production, due to large areas being taken over by old, decadent stands of tobosagrass (Hilaria mutica).

Grasshopper sparrows (Anunodramus savannarum), the only birds significantly affected by spring burning treatments in the grasslands of South Dakota, decreased in numbers immediately after fire. Western meadowlarks (Sturnella neglecta) generally decreased after the burns, while vesper sparrows increased (Forde et al 1984).

Huber and Steuter (1984) found similar trends in grasshopper sparrows and western meadowlarks after a spring grassland burn. Grasshopper sparrows were not present on the burned plots one month after the fire. Western meadowlarks decreased slightly after the fire, but within 2 months numbers were greater on the burned plots than on the control plots.

On a grassland in Minnesota, Tester and Marshall (1961) found that the presence of bobolinks (Dolichonyx oryzivorus), savannah sparrows (Passerculus sandwichensis), and LeConte's sparrows (Ammodramus leconteii) was positively correlated with the amount of litter cover present on the study site.

All three species declined after burns (fall and spring), though the authors believed there were other factors involved.

No bobolinks were present on the burned plots until after one season's litter had accumulated. Savannah sparrows showed similar responses; they required more than 2 years of litter accumulation. LeConte's sparrows appeared to need a moderate amount of litter cover in wet meadow zones. This species was not present until after one season of litter had accumulated.

Nest site selection

Habitat alteration by fire may change the nesting behavior of some birds. Kirsch et al (1978) stated that nongame birds that nest in upland areas are influenced by the amount and quality of available vegetation.

Winter and Best (1985) found a significant difference in nest placement between pre-burn and post-burn nesting seasons. The year previous to their burn, all sage sparrow nests found had been built within sagebrush canopies. After the burn, 17% of the nests were located in depressions on the ground under small sagebrush plants, and one nest was located in a bluebunch wheatgrass (Agropyron spicatum) clump.

Nest placement also differed significantly the first post-burn year. Fifty percent (6) of all early nests were built in sites other than sagebrush canopies, while all late nests (17) were within sagebrush plants. They concluded that the reduction of available sagebrush plants by fire required some of the sage sparrows to use areas other than their preferred habitat to obtain enough cover and concealment for their nests.

Foraging behavior

The immediate effect of fire on bird populations depends greatly upon the season and intensity of the burn. A relatively cool fire during the dormant season could greatly increase food sources (Wright and Bailey 1982). Birds are adapted to eat particular kinds of food, and the birds' abundance may depend largely on the supply of the appropriate kind of food (Bendell 1974).

Best (1979) found that the major impact of burning on foraging behavior was to make plant foods accessible, particularly grass seed that was unavailable before the burn because of the accumulation of grass litter. After burning, field sparrows were frequently observed picking up seeds from among the ashes.

Other bird species, especially wood thrushes (Hylocichla mustelina) but also gray catbirds (Dumetella carolinensis) and chipping sparrows (Spizella passerina), fed more frequently on the study area after the burn than in previous years.

McGee (1976) also found an influx of non-breeding birds to the burned areas in his study. He attributed this to the increased availability of plants and insects as food items.

Winter (1984) found sage sparrows spent significantly less time foraging in the post-burn period. Evidently, the foraging efficiency of sage sparrows increased after the fire, whereas Brewer's sparrow foraging efficiency remained unchanged.

Sage sparrows and Brewer's sparrows partitioned food resources by their foraging behavior. Brewer's sparrows foraged more often in the outer foliage of sagebrush than did sage sparrows, but sage sparrows utilized grasses, forbs, and bare ground more often than did Brewer's sparrows.

Fire caused male Brewer's sparrows to fly farther to unburned patches to forage, while the sage sparrows foraged in the burned areas. Differences in their foraging behavior after the fire reduced competition between these species. Winter (1984) also found that in late July burned patches contained more arthropods than unburned areas; with the reduced vegetative cover after burning, there was increased arthropod accessibility.

There is general agreement that fire reduces breeding pair density, alters nest site selection, and changes foraging behavior, at least during the first breeding season after the burn. The duration of the impact depends on the extent of the habitat alteration.

Forde et al (1984) found that two or three breeding seasons were required to increase bird species numbers to pre-burn densities.

The frequency of fire may render a habitat unsuitable for use by a given species, depending on its habitat requirements. When prescribed burning creates a fine-grained mosaic with good interspersion of habitat types and with a maintained edge, the greatest number of species requiring sub-climax vegetation will benefit (Best 1979; Winter 1984).

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