Date of this Version
There are no published, long-term accounts of responses of grassland passerine birds to the restoration of northern mixed-grass prairie through combined use of fire and grazing. During 1979-2001, we assessed abundance of passerine birds (9 grassland species and 1 shrub-associate species) on 2 brush-invaded, mixed-grass prairie tracts at Lostwood National Wildlife Refuge in northwestern North Dakota. Each tract encompassed 90 ha (220 ac) that were being restored through 4 prescribed fires then 3 consecutive years of grazing by cattle. Fires were separated by 2-4 years of rest (i.e., nondisturbance) and grazing was initiated 2 years after the last fire. Among 3 initially common species of passerines, abundance of Savannah sparrow (Passerculus sandwichensis) changed little from the beginning to end of the burn-graze sequence, but numbers of common yellowthroat (Geothlypis trichas) and clay-colored sparrow (Spizella pallida) declined. Six species of passerines, including the endemic Sprague's pipit (Anthus spragueii) and Baird's sparrow (Ammodramus bairdii), were absent or rare before restoration began but increased after burning occurred. Increases in abundance were most evident during rest years after the third and fourth burns, particularly for grasshopper sparrow (A. savannarum) and Baird's sparrow. Almost no increases occurred after the first burn. Changed abundances coincided with a shift from shrub-dominated to grass-dominated vegetation along with a decrease in vegetation structure; grass cover increased from 45% to 84% and a visual obstruction index that reflected vegetation height and density declined from 1.2 to 0.8 dm (4.7 and 3.1 in, respectively). During grazing, species abundance appeared unchanged except Sprague's pipit was not observed 2 of 3 years, and Baird's sparrow and grasshopper sparrow became less common. Our case history study supports the idea that the species diversity of breeding grassland birds can increase and be maintained when a combination of recurrent fire and grazing is used to restore degraded native prairie in the eastern part of the northern mixed-grass prairie region.