A survey of bluff forest avifauna in Southwestern Illinois.
The forested bluffs of southwestern Illinois attract large numbers of migrating songbirds due to their prime location near the confluence of the Mississippi, Missouri, and Illinois Rivers. These once extensive oak-hickory forests are now highly fragmented, initially due to agriculture and more recently due to increasing urbanization. As the St. Louis metropolitan area continues its rapid expansion eastward, protection and management of remaining forests is crucial. The campus of Southern Illinois University Edwardsville (SIUE) and adjacent Bohm Woods Nature Preserve include some of the largest remaining forest tracts in Madison County, Illinois.
Population declines have been noted for many neotropical migrants in Illinois (Robinson et al., 1995), and are hypothesized to be influenced by fragmentation of forests on breeding grounds (Gates and Evans, 1998; Robinson and Robinson, 2001), brood parasitism by Brown-headed Cowbirds (Robinson et al, 1995), deforestation in the tropics (Bollinger and Linder, 1994), invasion of exotic plants and increasing populations of browsers (Elphick et al., 2001) and predators (Heske et al., 2001). Our objective was to assess avian populations in several forest patches in southwestern Illinois in order to characterize existing habitat as well as to inform future land use decisions in this rapidly developing area.
The three forest patches included in the survey occur on or adjacent to the SIUE campus in Madison County, Illinois (Fig. 1). All occur on loess bluffs at the edge of the Mississippi River floodplain known as the American Bottoms. Sweet William Woods is the largest forest patch covering 59.7 ha. The majority of this mesic/dry-mesic upland forest was formerly agricultural land that has experienced recent regrowth (<50 years). Portions of the forest that are along ravines have had trees present for over 100 years. Sweet William Woods includes an extensive network of trails and experiences the greatest amount of foot traffic. Bluebell Woods is a smaller mesic/dry-mesic upland forest that covers 30.3 ha and has a similar history of disturbance. However, it lacks trails and experiences little foot traffic. Bohm Woods Nature Preserve is largely mesic/dry-mesic upland forest, but also includes portions of wet bottomland forest. It covers 25.6 ha and has a more uniform distribution of mature trees than the other two forest patches. In addition, it has had little logging disturbance and receives intermediate levels of human traffic. All three forests have abundant deer populations due to adjoining agricultural land coupled with minimal hunting pressure.
MATERIALS AND METHODS
Fixed-distance point-count surveys (25 m radius) were conducted from May-July, 2008 at 129 randomized plots on the SIUE campus and adjacent Bohm Woods Nature Preserve (Bluebell, n = 34; Bohm, n = 29; Sweet William, n = 66). Surveys were conducted daily from 0600-1000 hours except when raining, foggy, or excessively windy. Each survey included a 1 minute warm-up period, followed by a 5 minute sampling period. Before the warm-up period a laser rangefinder (Bushnell Yardage Pro 500) was used to mark distance in the 4 cardinal directions (unless prevented by vegetation). All birds seen or heard during the sampling period were recorded, but only species within the 25 m radius were used in population density estimates (Bibby et al., 2000). During the sampling period a digital voice recorder (Olympus DS-40) was used to record songs and calls for subsequent identification in the lab. Sites were chosen each day to maximize distance between sampling locations, and the most direct routes to those sites were traveled in order to minimize disturbance (Bibby et al., 2000). Plots were visited 3 times each for a total sampling effort of 32.25 hours.
Density estimates for each bird species assumed there was one female for each singing male recorded. Densities were then calculated within plots and scaled up to one hectare. Overall densities for each forest patch were summed across all plots and average densities were estimated. In addition, species richness (S; total number of species), Shannon's diversity index (H'loge; measure of diversity incorporating richness and evenness), and Hill's diversity index (N1; exponential of H'loge) were calculated for each forest patch using Primer 6 (Clarke and Gorley, 2008). Indicator species analysis (ISA) was used to identify bird species that best characterized each forest patch (Dufrene and Legendre, 1997). We used a liberal P-value of 0.2 for ISA since we intended it as an exploratory analysis rather than as an explicit test of hypotheses.
Species richness was highest for the largest forest patch, Sweet William Woods (S = 63), with Bluebell and Bohm Woods exhibiting identical richness (S = 45; Table 1). Species diversity, as measured by Shannon's diversity index, was similar between Sweet William (H'(loge) = 3.39) and Bohm Woods (H'(loge) = 3.38), despite a large difference in area. Bluebell Woods (30.3 ha) had the lowest species diversity (H'(loge) = 3.16; Table 1).
Tables 2-5 list the densities for each species within each forest patch. Overall, warbler population densities were relatively low throughout the three forest patches (<1 individual/ha; Table 2). Exceptions, included Northern Parula, which was abundant (>2 /ha) at all three sites, and Magnolia, Yellow, and Black-throated Green Warblers, which were moderately abundant in Bohm Woods (1-2 individuals/ha). Among other migratory passerines, densities exceeded 1 individual/ha at all three sites for Eastern Wood-Pewee, Acadian Flycatcher, Wood Thrush, Great Crested Flycatcher, Indigo Bunting, Blue-gray Gnatcatcher, and Red-eyed Vireo (Table 3). In addition, Swainson's Thrush and White-throated Sparrow were abundant in Bohm Woods. Among resident passerines, Tufted Titmouse, Northern Cardinal, American Goldfinch, Brown-headed Cowbird, Eastern Towhee, Carolina Chickadee, White-breasted Nuthatch, Carolina Wren, and American Robin were abundant at all three sites. The Blue Jay was abundant at Bluebell and Sweet William Woods. (Table 4). Among nonpasserines, Red-bellied and Downy Woodpeckers were abundant at all three sites; whereas, Ruby-throated Hummingbird, Chimney Swift, Northern Flicker, and Hairy Woodpecker were abundant at Bohm Woods (Table 5).
Table 6 describes the results of the indicator species analysis (ISA). Seven species were identified whose relatively high indicator values acted to differentiate Bluebell Woods from the remaining forest patches. These included Northern Cardinal, American Goldfinch, Tufted Titmouse, Eastern Towhee, Blue-gray Gnatcatcher, Common Grackle, and Black-capped Chickadee. Three species differentiated Sweet William from the other forests: Carolina Chickadee, Carolina Wren, and Kentucky Warbler. Lastly, 12 species served as indicators for Bohm Woods: Acadian Flycatcher, American Robin, Ruby-throated Hummingbird, Downy woodpecker, Wood Thrush, Hairy Woodpecker, Chimney Swift, Northern Flicker, Yellow Warbler, White-throated Sparrow, Black-throated Green Warbler, and Swainson's Thrush.
Table 7 lists additional species encountered during the sampling period outside of 25 m plots and not included in species richness or density estimates. Table 8 lists additional species encountered outside of the sampling period and not included in species richness or density.
We identified 90 species among three forest patches on and adjacent to the Southern Illinois University Edwardsville campus, including species of conservation concern such as the state threatened Black-billed Cuckoo (proposed) and the state endangered Northern Harrier. Bohm Woods appears to be particularly valuable from a conservation perspective. It is the only patch to feature migratory transients as indicator species, including Black-throated Green Warbler and Swainson's Thrush (Table 6). This suggests an important role as a migratory stopover site, despite its small size. Nevertheless, Bohm Woods is also comprised of relatively undisturbed mature forest which may make it more attractive than larger forest patches with greater levels of disturbance. In addition, Bohm Woods is also distinguished by supporting higher numbers of forest interior species, including two Neotropical migrants sensitive to fragmentation, Acadian Flycatcher and Wood Thrush (Roth et al., 1996; Whitehead and Taylor, 2002; Table 6).
The Acadian Flycatcher breeds near water in deciduous forests of the Midwest (Whitehead and Taylor, 2002). They have been found to exhibit low reproductive success within 600 m of a forest edge in southern Illinois due to cowbird parasitism and predation resulting from fragmentation (Hoover et al., 2006). None of the forest patches surveyed in the present study include habitat greater than 600 m from an edge. This would seem to make the entire area a population sink for Acadian Flycatchers. However, another study in Illinois determined that Acadian Flycatchers may be less sensitive to fragmentation than other forest passerines in Illinois and may exhibit reproductive success in narrow riparian corridors (Chapa-Vargas and Robinson, 2007). The extensive network of ravines, transitioning to wet, bottomland forest in Bohm Woods may provide ideal conditions for Acadian Flycatchers, as evidenced by the high density estimates (6.79/ha; Table 6). The degree of reproductive success should be monitored to determine which of these two scenarios characterizes this population.
Wood Thrushes in Illinois also exhibit low nesting productivity due to the effects of forest fragmentation. Forest patches as large as 2200 ha have been found to be population sinks (Trine, 1998). Given the small size of the forest patches in the present study, local populations are likely to exhibit low recruitment. Nevertheless, Bohm Woods attracts relatively large numbers of Wood Thrush due to its mature trees. Despite its likely status as a population sink, it undoubtedly has value as a migratory stopover site.
Bohm Woods exhibited the lowest Brown-headed Cowbird density of the three forest patches (Table 4). Brown-headed Cowbirds are brood parasites that lay their eggs in the nests of many avian host species, providing no additional parental investment. The hosts may then incubate and rear cowbird offspring to the detriment of their own fitness (Brittingham and Temple, 1983). Cowbirds forage in agricultural areas and are typically more abundant at forest edge rather than forest interior (Lowther, 1993). Despite its small size and close proximity to agriculture, Bohm Woods may be less attractive to cowbirds than larger surrounding patches due to its mature trees and circular shape, which maximizes the amount of interior forest habitat.
Sweet William and Bluebell Woods are comprised of large areas of regrowth and are characterized by higher numbers of bird species associated with this habitat type (Table 6). However, they maintain core areas of mature trees, concentrated around ravines. These areas are important for forest interior bird species and should be protected from future disturbance. As the surrounding forest continues to mature, the value for interior species will increase.
Efforts should be made to acquire additional land and convert adjacent non-forested land to forest in order to benefit forest interior species. Although, young forest would be of little direct value to these species in terms of suitable foraging or nesting habitat, it would serve an important indirect role by providing a buffer to cowbirds and predators. This is critical for Bohm Woods which has higher numbers of sensitive species.
Bluff forest avifauna should continue to be observed over the long term in order to monitor population trends. This is especially important due to current and predicted changes in vegetation. Long-term monitoring may allow elucidation of the effects of rapid expansion of bush honeysuckle (Lonicera maackii), as well as the predicted loss of ash (Fraxinus sp.) from these forests. The plots used in this study are permanently marked and georeferenced and we intend to resample them regularly in the future to monitor changes in the vegetation and bird communities.
This is contribution number 30 of the National Great Rivers Research and Education Center. We thank the Illinois Nature Preserves Commission for permission to conduct research in Bohm Woods Nature Preserve. We thank David Hartweger, Jerrod Looft, and Felicia Scaggs for assistance with establishing research plots and Bill Retzlaff for loaning the rangefinder. This research was supported in part by grants from the National Great Rivers Research and Education Center, the Illinois Department of Natural Resources Wildlife Preservation Fund and the Illinois Ornithological Society/Du Page Birding Club.
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Lane A. Richter, Richard L. Essner, Jr., and Peter R. Minchin Department of Biological Sciences Southern Illinois University Edwardsville, IL 62026, USA Correspondence: firstname.lastname@example.org
Table 1. Species richness (S), Shannon (H' loge) and Hill (N1) diversity indices for 3 forest patches in Madison County, Illinois. Forest S H'([log.sub.e]) N1 Bluebell 45 3.16 23.6 Bohm 45 3.38 29.5 Sweet William 63 3.39 29.6 Table 2. Estimated population densities (individuals/ha) for warblers in 3 forest patches in Madison County, IL Species Common Name Dendroica coronata Yellow-rumped Warbler Dendroica dominica Yellow-throated Warbler Dendroica fusca Blackburnian Warbler Dendroica magnolia Magnolia Warbler Dendroica pensylvanica Chestnut-sided Warbler Dendroica petechia Yellow Warbler Dendroica striata Blackpoll Warbler Dendroica virens Black-throated Green Warbler Geothlypis trichas Common Yellowthroat Mniotilta varia Black-and-white Warbler Oporornis formosus Kentucky Warbler Oporornis philadelphia Mourning Warbler Parula americana Northern Parula Seiurus aurocapilla Ovenbird Seiurus motacilla Louisiana Waterthrush Setophaga ruticilla American Redstart Vermivora peregrina Tennessee Warbler Vermivora ruficapilla Nashville Warbler Wilsonia citrina Hooded Warbler Species Bluebell Bohm Sweet William Dendroica coronata 0.60 0.34 0.15 Dendroica dominica 0.00 0.34 0.15 Dendroica fusca 0.30 0.00 0.15 Dendroica magnolia 0.30 1.02 0.23 Dendroica pensylvanica 0.00 0.85 0.62 Dendroica petechia 0.00 1.53 0.31 Dendroica striata 0.00 0.00 0.46 Dendroica virens 0.00 1.02 0.15 Geothlypis trichas 0.60 0.00 0.15 Mniotilta varia 0.00 0.00 0.15 Oporornis formosus 0.00 0.00 0.39 Oporornis philadelphia 0.00 0.17 0.00 Parula americana 4.19 2.55 3.70 Seiurus aurocapilla 0.00 0.34 0.31 Seiurus motacilla 0.00 0.00 0.46 Setophaga ruticilla 0.30 0.51 0.39 Vermivora peregrina 0.30 0.34 0.31 Vermivora ruficapilla 0.00 0.00 0.15 Wilsonia citrina 0.00 0.34 0.00 Table 3. Estimated population densities (individuals/ha) for other (non-warbler) migratory passerines in 3 forest patches in Madison County, IL. Species Common Name Catharus fuscescens Veery Catharus ustulatus Swainson's Thrush Contopus virens Eastern Wood-Pewee Dumetella carolinensis Gray Catbird Empidonax alnorum Alder Flycatcher Empidonax flaviventris Yellow-bellied Flycatcher Empidonax virescens Acadian Flycatcher Hylocichla mustelina Wood Thrush Icterus galbula Baltimore Oriole Myiarchus crinitus Great Crested Flycatcher Passerina cyanea Indigo Bunting Pheucticus ludovicianus Rose-breasted Grosbeak Piranga olivacea Scarlet Tanager Piranga rubra Summer Tanager Polioptila caerulea Blue-gray Gnatcatcher Sayornis phoebe Eastern Phoebe Spizella passerine Chipping Sparrow Toxostoma rufum Brown Thrasher Troglodytes aedon House Wren Tyrannus tyrannus Eastern Kingbird Vireo flavifrons Yellow-throated Vireo Vireo gilvus Warbling Vireo Vireo griseus White-eyed Vireo Vireo olivaceus Red-eyed Vireo Vireo philadelphicus Philadelphia Vireo Zonotrichia albicollis White-throated Sparrow Species Bluebell Bohm Sweet William Catharus fuscescens 0.00 0.00 0.15 Catharus ustulatus 0.60 1.53 0.08 Contopus virens 2.10 1.36 2.39 Dumetella carolinensis 0.00 0.00 0.23 Empidonax alnorum 0.00 0.00 0.15 Empidonax flaviventris 0.30 0.00 0.46 Empidonax virescens 2.10 6.79 2.16 Hylocichla mustelina 1.95 4.07 2.08 Icterus galbula 0.00 0.34 0.08 Myiarchus crinitus 2.40 1.19 3.47 Passerina cyanea 5.69 8.49 4.01 Pheucticus ludovicianus 0.15 0.34 0.00 Piranga olivacea 0.00 0.00 0.46 Piranga rubra 0.00 0.34 0.08 Polioptila caerulea 4.04 1.19 2.47 Sayornis phoebe 0.00 0.00 0.08 Spizella passerine 0.30 0.00 0.15 Toxostoma rufum 0.30 0.00 0.15 Troglodytes aedon 0.30 0.00 0.85 Tyrannus tyrannus 0.30 0.00 0.08 Vireo flavifrons 0.00 0.34 0.15 Vireo gilvus 0.00 0.00 0.15 Vireo griseus 0.30 0.00 0.31 Vireo olivaceus 6.89 5.09 5.63 Vireo philadelphicus 0.00 0.34 0.31 Zonotrichia albicollis 0.15 1.02 0.00 Table 4. Estimated population densities (individuals/ha) for resident passerines in 3 forest patches in Madison County, IL. Species Common Name Agelaius phoeniceus Red-winged Blackbird Baeolophus bicolor Tufted Titmouse Cardinalis cardinalis Northern Cardinal Carduelis tristis American Goldfinch Corvus brachyrhynchos American Crow Cyanocitta cristata Blue Jay Mimus polyglottos Northern Mockingbird Molothrus ater Brown-headed Cowbird Pipilo erythrophthalmus Eastern Towhee Poecile atricapilla Black-capped Chickadee Poecile carolinensis Carolina Chickadee Quiscalus quiscula Common Grackle Sialia sialis Eastern Bluebird Sitta carolinensis White-breasted Nuthatch Sturnus vulgaris European Starling Thryothorus ludovicianus Carolina Wren Turdus migratorius American Robin Species Bluebell Bohm Sweet William Agelaius phoeniceus 0.60 0.34 0.00 Baeolophus bicolor 7.79 5.77 5.09 Cardinalis cardinalis 12.58 6.45 9.80 Carduelis tristis 11.38 4.24 4.48 Corvus brachyrhynchos 0.75 0.00 0.77 Cyanocitta cristata 1.50 0.68 1.62 Mimus polyglottos 0.00 0.00 0.31 Molothrus ater 5.09 2.89 4.63 Pipilo erythrophthalmus 5.54 1.53 3.63 Poecile atricapilla 1.05 0.00 0.00 Poecile carolinensis 5.69 2.89 7.18 Quiscalus quiscula 1.80 0.00 0.62 Sialia sialis 0.00 0.00 0.15 Sitta carolinensis 0.75 2.21 2.24 Sturnus vulgaris 0.30 0.00 0.00 Thryothorus ludovicianus 1.20 1.70 2.86 Turdus migratorius 2.40 4.92 1.77 Table 5. Estimated population densities (individuals/ha) for nonpasserines in 3 forest patches in Madison County, IL. Species Common Name Archilochus colubris Ruby-throated Hummingbird Chaetura pelagica Chimney Swift Coccyzus americanus Yellow-billed Cuckoo Colaptes auratus Northern Flicker Dryocopus pileatus Pileated Woodpecker Melanerpes carolinus Red-bellied Woodpecker Meleagris gallopavo Wild Turkey Picoides pubescens Downy Woodpecker Picoides villosus Hairy Woodpecker Species Bluebell Bohm Sweet William Archilochus colubris 0.60 2.55 0.39 Chaetura pelagica 0.00 1.70 0.00 Coccyzus americanus 0.90 0.68 0.46 Colaptes auratus 0.45 1.36 0.15 Dryocopus pileatus 0.30 0.85 0.46 Melanerpes carolinus 1.35 2.55 2.16 Meleagris gallopavo 0.00 0.00 0.15 Picoides pubescens 3.15 3.90 2.08 Picoides villosus 0.75 2.21 0.85 Table 6. Indicator species analysis for 3 forest patches in Madison County, IL. Tabulated indicator values are the product of fidelity and constancy. P values are based on 10,000 random permutations of group membership. Species with P < 0.2 are shown. A liberal P-value of 0.2 since was used since this was an exploratory analysis rather than an explicit test of hypotheses. Bold values indicate the group for which the species is a significant indicator. Species Common Name Baeolophus bicolor Tufted Titmouse Cardinalis cardinalis Northern Cardinal Carduelis tristis American Goldfinch Pipilo erythrophthalmus Eastern Towhee Poecile atricapillus Black-capped Chickadee Polioptila caerulea Blue-gray Gnatcatcher Quiscalus quiscula Common Grackle Archilochus colubris Ruby-throated Hummingbird Catharus ustulatus Swainson's Thrush Chaetura pelagica Chimney Swift Colaptes auratus Northern Flicker Dendroica petechia Yellow Warbler Dendroica virens Black-throated Green Warbler Empidonax virescens Acadian Flycatcher Hylocichla mustelina Wood Thrush Picoides pubescens Downy Woodpecker Picoides villosus Hairy Woodpecker Turdus migratorius American Robin Zonotrichia albicollis White-throated Sparrow Oporornis formosus Kentucky Warbler Poecile carolinensis Carolina Chickadee Thryothorus ludovicianus Carolina Wren Sweet Species Bluebell Bohm William P Baeolophus bicolor 26 14 12 0.1401 Cardinalis cardinalis 35 16 28 0.1058 Carduelis tristis 32 8 8 0.0055 Pipilo erythrophthalmus 20 3 12 0.1258 Poecile atricapillus 6 0 0 0.1181 Polioptila caerulea 19 3 9 0.1053 Quiscalus quiscula 11 0 2 0.0385 Archilochus colubris 1 17 0 0.0051 Catharus ustulatus 1 9 0 0.037 Chaetura pelagica 0 13 0 0.0027 Colaptes auratus 1 12 0 0.0213 Dendroica petechia 0 11 1 0.0149 Dendroica virens 0 9 0 0.0313 Empidonax virescens 3 41 4 0.0001 Hylocichla mustelina 4 15 5 0.124 Picoides pubescens 10 17 4 0.125 Picoides villosus 2 14 2 0.0559 Turdus migratorius 6 20 4 0.0409 Zonotrichia albicollis 0 9 0 0.0155 Oporornis formosus 0 0 6 0.1546 Poecile carolinensis 18 7 25 0.1737 Thryothorus ludovicianus 2 7 17 0.1497 Table 7. Observations of additional species encountered during sampling period outside of 25 m plots and not included in species richness or density estimates. Species Common Name Branta canadensis Canada Goose Buteo jamaicensis Red-tailed Hawk Cathartes aura Turkey Vulture Catharus guttatus Hermit Thrush Charadrius vociferous Killdeer Coccyzus erythropthalmus Black-billed Cuckoo Colinus virginianus Northern Bobwhite Dendroica tigrina Cape May Warbler Helmitheros vermivorum Worm-eating Warbler Passerina caerulea Blue Grosbeak Spizella pusilla Field Sparrow Sturnella magna Eastern Meadowlark Vermivora pinus Blue-winged Warbler Zenaida macroura Mourning Dove Species Bluebell Bohm Sweet William Branta canadensis 11 4 7 Buteo jamaicensis -- 2 -- Cathartes aura 2 1 -- Catharus guttatus -- 1 3 Charadrius vociferous 1 -- -- Coccyzus erythropthalmus 1 -- 1 Colinus virginianus 3 3 5 Dendroica tigrina 1 -- -- Helmitheros vermivorum -- -- 2 Passerina caerulea -- -- -- Spizella pusilla 11 3 8 Sturnella magna 1 -- -- Vermivora pinus 1 -- -- Zenaida macroura 3 1 2 Table 8. Observations of additional species encountered outside of sampling period and not included in species richness or density estimates. Species Common Name Circus cyaneus Northern Harrier Megaceryle alcyon Belted Kingfisher Strix varia Barred Owl Vermivora chrysoptera Golden-winged Warbler Vireo bellii Bell's Vireo Species Bluebell Bohm Sweet William Circus cyaneus -- 1 -- Megaceryle alcyon -- 1 -- Strix varia -- 1 -- Vermivora chrysoptera -- 1 -- Vireo bellii -- -- 1
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|Author:||Richter, Lane A.; Essner, Richard L., Jr.; Minchin, Peter R.|
|Publication:||Transactions of the Illinois State Academy of Science|
|Date:||Jan 1, 2010|
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