BIRD COMMUNITIES OF RESTORED BARRENS AND BURNED
FORESTS OF SOUTHERN ILLINOIS
Scott K. Robinson
The effects of barrens and savanna restoration on midwestern wildlife communities remain poorly understood in spite of widespread use of fire to restore these plant communities. A few forest bird species such as the Red-cockaded Woodpecker and the Bachman's Sparrow, are known to depend upon fire (Lennartz 1984; Hardin et al. 1982). Some birds of more open canopies may benefit from savanna restoration, but there is also a possibility that restoration will favor the generalist and edge-preferring species that also thrive in landscapes disturbed by other human activities. Similarly, opening the canopy and eliminating much of the middle story could attract species such as the brood parasitic Brown-headed Cowbird, which adversely affects the nesting success of forest birds (Robinson et al. 1993).
The purpose of this paper is to compare bird communities of barrens and burned forest (savannas) bird communities with those of unburned forests in southern Illinois. The goals of this study were to: 1) determine which species benefit from fire restoration efforts and which species may be negatively affected, 2) compare populations of predatory Blue Jays and Brown-headed Cowbirds in burned and unburned forests, and 3) gather preliminary data on the effects of differing inter-burn intervals on bird communities.
Bird communities were censured in southern Illinois in 7 counties (Jackson, Union, Alexander, Johnson, Pope, Saline, and Hardin). Most of the barrens and burned forests were located in the Shawnee National Forest, although some were also located on land managed by the Illinois Department of Conservation, including the Trail of Tears State Forest and Cache River State Natural Area.
Bird communities were censured using a modified version of the fixed radius point count method of Hutto et al. (1986). Points were located as close to the center of the barren or burn unit as possible and all birds heard or observed within a 70 m radius during a 6-min count period were recorded. Birds that were heard in adjacent unburned forest were recorded separately. All censuses were conducted between 0520-1200 between 15 May-10 July, 1993. For the purposes of this paper, I only use data from upland, ridgetop censuses on mesic-dry soil types. Bird communities of mesic-wet ravine bottoms and floodplain forests are different from those on drier ridges; their inclusion in this census would complicate interpretation of the effects of restoration efforts using fire. Ridgetop censuses from unburned sections of the Shawnee National Forest (Pine Hills, Atwood Ridge) and Trail of Tears State Forest were used for comparisons. Pre- and post-burning comparisons were made in the Pine Hills Ecological Study Area. As of the preparation of this manuscript, data analysis is not complete; therefore I present only preliminary analysis of the data.
Censuses of barrens, savannas (burned woodlands), and unburned upland forests show several striking differences in relative abundances and species composition (Table 1). Compared with unburned forests, burned areas had higher abundances of Yellow-billed Cuckoos, Eastern Wood-Pewees, Blue-gray Gnatcatchers, Yellow-throated Vireos, Summer Tanagers, Northern Cardinals, Indigo Buntings, and Brown-headed Cowbirds and lower abundances of Acadian Flycatchers, Wood Thrushes, Red-eyed Vireos, Cerulean Warblers, Worm-eating Warblers and Ovenbirds. Indigo Buntings were virtually absent from unburned forest and Red-eyed Vireos, Worm-eating Warblers, and Ovenbirds were absent or very rare in burn units.
Barrens communities censured were small (<2 ha) and contained relatively higher populations of Yellow-billed Cuckoos, Ruby-throated Hummingbirds, Downy Woodpeckers, Eastern Wood-Pewees, Great Crested Flycatchers, Carolina Chickadees, Kentucky Warblers, Summer Tanagers, Northern Cardinals, Indigo Buntings, Rufous-sided Towhees, and Brown-headed Cowbirds than unburned, closed-canopy forests. Barrens communities had lower populations of Blue Jays, Red-eyed Vireos, Worm-eating Warblers, Ovenbirds, and Scarlet Tanagers than unburned forests. Relative to burned forests with more closed canopies, barrens contained more Mourning Doves, Ruby-throated Hummingbirds, Great Crested Flycatchers, Carolina Chickadees, Kentucky Warblers, and Indigo Buntings, but fewer Yellow-throated Vireos and Scarlet Tanagers. The small barrens communities censused in Illinois contained only low populations of species of more open habitats (e.g., Eastern Kingbird, Eastern Bluebird, American Robins, Brown Thrasher, White-eyed Vireo, Common Yellowthroat, Field Sparrows, Orchard and Northern orioles) and were lacking many species associated with more extensive shrublands (e.g., Bewick's Wren, Gray Catbird, Bell's Vireo, Blue-winged and Prairie warblers, Yellow-breasted Chat, Blue Grosbeak, and Bachman's Sparrow).
Reintroducing fire to oak woodlands and restoring barrens communities will substantially alter bird communities. The species most characteristic of the savanna/barrens communities censured in southern Illinois appear to be the Eastern Wood-Pewee, Great Crested Flycatcher (barrens), Blue-gray Gnatcatcher, Northern Cardinal and, especially, the Summer Tanager and Indigo Bunting. These latter two species were more abundant in barrens and savannas than they were in any other forest habitat I have censured in Illinois (S. Robinson, unpublished data). All of these species, however, also breed commonly in the other forest and non-forest habitats in the Midwest and none are of special conservation concern. The species that appear to be incompatible with burning include several species characteristic of dense understory and lower canopy layers (e.g., Acadian Flycatcher, Wood Thrush, Red-eyed Vireo, Worm-eating Warbler, Hooded Warbler) or open ground layers (Ovenbird). All of these species, however, at least occasionally occupy burned areas and Hooded Warblers occupied two older (> 2 year post-burning) plots. These results suggest that the abundance of birds of the forest shrub/sapling and ground layers will be strongly affected by the timing of burns.
The relatively closed canopies of most burned savannas in southern Illinois might exclude some of the birds more characteristic of open savannas. Red-headed Woodpeckers, Eastern Kingbirds, Warbling Vireos, American Robins, and Chipping Sparrows, for example, nest in some of the more open savannas in central and northern Illinois (S. Robinson and J. Brawn, unpublished data).
The small barrens communities censured in southern Illinois appear to be too small to sustain populations of species that might be barrens specialists (e.g., Bachman's Sparrow). Instead, these barrens are mostly occupied by forest birds that prefer more open canopies or canopy gaps (e.g., Eastern Phoebe, Great Crested Flycatcher, Carolina Chickadee, Blue-gray Gnatcatcher, Summer Tanager, and Indigo Bunting). Restoring the full range of barrens bird communities will likely require larger-scale restoration efforts. Similarly, careful consideration will have to be given to the role of shrubby vegetation in barrens; the presence of Blue-winged and Prairie warblers and Bell's Vireos will likely depend upon the presence of at least some shrubby vegetation.
The very high abundance of cowbirds in both barrens and burned forests suggests that brood parasitism may be a substantial problem for most host species. Very high cowbird abundance is a reliable predictor of high parasitism levels throughout Illinois (Robinson et al., In press). For these reasons, management with fire might exacerbate the already formidable problem of cowbird parasitism in fragmented landscapes (Robinson et al., In press).
In conclusion, how restoration of barrens and savanna plant communities will affect bird communities will depend upon a variety of factors including the severity of the burn, the openness of the canopy, the duration of the inter-burn interval, and the size of the burn unit. Many forest bird species will be adversely affected; if burning is restricted to drier ridgetops, however, most forest birds might have refuges in more mesic ravines. We need studies of productivity of forest birds before we can fully evaluate the impact of savanna and barrens restoration.
Hardin, K. I., T. S. Baskett and K. E. Evans. 1982. Habitat of Bachman's Sparrow breeding on Missouri glades. Wilson Bulletin 94:208-212.
Hutto, R.L., S. M. Pletschet and P. Hendricks. 1986. A fixed -radius point count method for nonbreeding and breeding season use. Auk 103:593-602.
Lennartz, M. R. 1984. Red-cockaded Woodpecker recovery plan. Atlanta, GA: U.S. Department of the Interior, Fish and Wildlife Service. 66p.
Robinson, S. K., J. A. Grzybowski, S. I. Rothstein, L. J. Petit, M. C. Brittingham, and F. R. Thompson, III. 1993. Management implications of cowbird parasitism for neotropical migratory birds. U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, GTR RM-229, Fort Collins, CO.
TABLE 1. Relative abundances of birds in savanna (burned forest), barrens (all < 2 ha), and unburned upland forest in southern Illinois, 1993.
No./Point (70-m radius( (N)
|Yellow Billed Cuckoo||0.35||0.36||0.14|
|Great Crested Flycatcher||0.29||0.64||0.30|