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Effects of Field Borders on Breeding and Wintering Avian Communities
Ross R. Conover1, Eric T. Linder1, Loren W. Burger2, and Trey Cooke3
Abstract
1- Dept. of Biological Sciences, Mississippi State University, Starkville, MS 2-Dept. of Wildlife and Fisheries, Mississippi State University, Starkville, MS 3- Delta Wildlife,
Stoneville, MS
Agricultural trends have considerably altered the amount of suitable habitat for
grassland birds. These trends may be associated with the population declines of several
wintering and breeding bird species in the southeastern U.S. Grassland birds are
expected to benefit from uncultivated field borders. Despite the popular support of the
National Conservation Buffer Initiative, it has not been adequately evaluated for
nongame species. Consequently, we established field borders in the spring of 2002
with native warm season grasses (NWSG), most were 10m in width. Control areas
(representing current agricultural practices) were also established. All borders were
located between an active field and adjacent riparian strip. Comparisons of avian
abundance and richness between treatments were limited to birds within the 10-m
borders in the breeding season and 10-m borders plus 30-m of adjacent field in the
winter to minimize extrinsic bias. During the winter, we detected a pronounced
increase in avian abundance and richness of the treated borders compared to the
controls. Results indicate during the breeding season of 2003, treated borders had
greater avian abundance and richness than control borders, but not in 2002. There was
also a noticeable increase in abundance and richness within treated borders from 2002
to 2003, and a decrease in the control borders. This was likely due to the delayed
emergence of planted vegetation in the summer of 2002. Nesting density was
considerably greater in the wider borders than the 10-m borders. The preliminary
results of this research suggest that the establishment of uncultivated field borders may
provide suitable habitat to breeding and wintering birds in the Mississippi Alluvial
Valley (MAV), and that nesting density appears to be positively correlate with area.
Name
Red-winged Blackbird
Northern Cardinal
Dickcissel
Common Grackle
Mourning Dove
Blue Jay
Indigo Bunting
Carolina Wren
Yellow-billed Cuckoo
Brown-headed Cowbird
Red-bellied Woodpecker
Northern Mockingbird
Horned Lark
Killdeer
Carolina Chickadee
Barn Swallow
Eastern Towhee
Northern Bobwhite
Eastern Meadowlark
Downy Woodpecker
Orchard Oriole
Tufted Titmouse
Great Egret
American Robin
Brown Thrasher
Species
Agelaius phoenicius
Cardinalis cardinalis
Spiza americana
Quiscalus quiscula
Zenaida macroura
Cyanocitta cristata
Passerina cyanea
Thryothorus ludovicianus
Coccyzus americana
Molothrus ater
Melanerpes carolinus
Mimus polyglottus
Eremophila alpestris
Charadrius vociferus
Poecile carolinensis
Hirundo rustica
Pipilo erythropthalmus
Colinus virginianus
Sturnella magna
Picoides pubescens
Icterus spurius
Parus bicolor
Ardea alba
Turdus migratorius
Toxostoma rufum
RelAbu
0.3275
0.1034
0.0698
0.0659
0.0581
0.0505
0.0359
0.0359
0.0306
0.026
0.0216
0.0183
0.0178
0.0165
0.0159
0.0128
0.0111
0.0107
0.0103
0.009
0.0043
0.004
0.0038
0.0027
0.0024
Early successional habitat is sporadic in the MAV, where the landscape is dominated by
intensively managed farms. Field borders that remain vegetated year round were established
to provide farmland birds with suitable habitat. The potential value of field border habitat has
not been extensively researched in the southeastern U.S., although others have found it is
utilized for nesting cover, escape cover, and enhanced foraging (Puckett et al. 1995, Marcus
et al. 2000). During the breeding season, grassland birds are limited by the lack of suitable
nesting habitat. During the winter, farm fields are tilled, and therefore provide no cover and
little food. It is thought the resources provided by these borders may reduce the stresses
placed on farmland birds (Puckett et al. 1995).
2003.
Hypotheses
Hypothesis 1— Mean abundance and richness
within the 10-m field borders will be greater in
treated borders than control borders during the
breeding season.
Name
European Starling
Common Grackle
Mourning Dove
American Pipit
Northern Cardinal
Blue Jay
Killdeer
Song Sparrow
Red-bellied Woodpecker
White-throated Sparrow
Horned Lark
Carolina Wren
Red-winged Blackbird
Yellow-rumped Warbler
Carolina Chickadee
Swamp Sparrow
American Robin
Brown-headed Cowbird
Golden-crowned Kinglet
Double-crested Cormorant
Downy Woodpecker
Eastern Phoebe
Mallard
Red-tailed Hawk
Northern Flicker
Northern Mockingbird
Ruby-crowned Kinglet
Species
Sturna vulgaris
Quiscalus quiscula
Zenaida macroura
Anthus rubescens
Cardinalis cardinalis
Cyanocitta cristata
Charadrius vociferus
Melospiza melodia
Melanerpes carolinus
Zonotrichia albicollis
Eremophila alpestris
Thryothorus ludovicianus
Agelaius phoenicius
Dendroica coronata
Poecile carolinensis
Melospiza georgiana
Turdus migratorius
Molothrus ater
Regulus satrapa
Phalacrocorax auritus
Picoides pubescens
Sayornis phoebe
Anas platyrhynchos
Buteo jamaicensis
Colaptes auratus
Mimus polyglottus
Regulus calendula
RelAbu
0.2367
0.1837
0.176
0.0325
0.0316
0.0304
0.0292
0.0267
0.0238
0.021
0.0164
0.0136
0.0132
0.0119
0.0107
0.0107
0.009
0.009
0.0066
0.0062
0.0053
0.0049
0.0049
0.0049
0.0045
0.0045
0.0045
A.
Hypothesis 3—Nesting density will be positively
correlated with area in the treated borders.
B.
Nest densities revealed a positive correlation with increasing width (Fig. 3),
although this relationship was not significant (P=0.12; R2=0.60). The lack of
statistical significance is likely attributable to the small sample size and not the
lack of correlation. We failed to find any nests on our 10-m control borders
(N=19) throughout the breeding season. Conversely, the 10-m treated borders
averaged 9 nests/10 hectares (ha) and wider borders yielded even higher densities.
A.
B.
Grassland patch size has been documented to positively correlate with avian richness, nest
density, and nesting success. Such patterns may be related to habitat width sensitivity, which
is driven by edge aversion in several species (Winter and Faaborg 1999, Winter et al. 2000, Fig. 1: A- Differences in avian richness.
Helzer and Jelinski 1999). Wider plots may also be beneficial to reproductive success, as
B- Differences in total avian abundance.
increased patch size will decrease edge effects such as increased nest predation and brood
parasitism (Johnson and Temple 1990, Donovan et al. 1997)
Results
The overall avian community observed utilizing the borders was diverse during
both the summer and winter transect counts (Table 1 & 2), although species
encountered were largely determined by the presence of a wood line. We detected
no significant difference in abundance and richness between treated and untreated
10-m borders during the breeding season of 2002. However, in 2003 significant
differences in avian abundance (P<0.05; Fig. 1) and richness (P<0.05; Fig. 1)
were detected. During the winter, avian abundance between treated and untreated
borders was significant (P<0.05) while differences in richness were suggestive
(P=0.087).
Hypothesis 2— Mean abundance and richness
within the 10-m borders plus 30-m of the adjacent
field will be higher in treated borders than control
borders during the winter.
Introduction
The past century has witnessed astounding agricultural advances (machinery, herbicides,
pesticides, and transgenic crops), urban development, and increased farm field openings.
Such land use alterations have strikingly reduced and fragmented grassland habitat that is
crucial for wildlife (Herkert 1994, Marcus et al. 2000). This loss of suitable wildlife habitat
on farms has coincided with drastic population declines of several farmland bird species
(Warner 1994).
Table 2. Relative abundance of the field
border avian community during the winter
Table 1. Relative abundance of the field
border avian community during the summer
2003.
Discussion
There are numerous mechanisms that may influence the structure of the avian
community near the established field borders. Current farming practices in the
MAV leave little habitat suitable for wildlife by reducing nesting opportunities,
as well as foraging and escape cover in the winter. Field borders comprised of
grass provide crucial wildlife habitat that is extremely sparse in this region. The
benefits of such borders have been documented elsewhere, but despite the
popularity of the Conservation Buffer Initiative, it has not been adequately
evaluated. Our study thus far has documented uncultivated field borders
support greater abundance and diversity of breeding and wintering birds in the
MAV. This result is likely driven by the creation of additional vegetative
structure within the treated borders. The strong correlation of avian abundance
and richness in treated borders and adjacent fields in the winter is likely caused
by standing vegetation, providing suitable escape cover.
Nesting success is negatively associated with proximity to edge, and habitat
suitability decreases toward a field-forest edge (Johnson and Temple 1990). If
birds are responding to this pressure, nesting densities are therefore expected to
increase in wider grassland borders. Our data strongly suggests that treated
borders of greater widths harbored considerably more nests than the 10-m
borders, suggesting while 10-m borders provide some conservation benefit,
wider borders provide more. We hope to increase our sample of wide borders in
subsequent field seasons.
Acknowledgements
Fig. 2: A- Differences in richness in the winter.
B-Differences in total abundance in the winter.
The goal of this study is to evaluate the benefit of uncultivated field borders for birds during
the breeding and wintering season.
The authors are grateful for the hardwork of field assistants N. Rayman,
G. Conover, C. Leumas, W. Decaluwe, K. Nichols, E. Rexroad, L. Smith,
M. Haas, A. Peterson, and K. Davis. Jones Planting Co., P. Arrington,
Hopeso Farms, R. Allen, and F. Anderson all assisted the research by
permitting access to their land. We are also appreciative of the
contributions from USDA-NRCS, Duncan Gin Inc., and Delta Wildlife.
Experimental Design
Literature Cited
Study Site-- Our plots are situated throughout Sunflower County in the Mississippi Alluvial Valley. This region was historically covered
in bottomland hardwood forests. The landscape has little topographical relief and is dominated by agricultural farms fragmented by
irrigation ditches, streams, and wood lines.
Study Plots-- Twenty-seven-10X400m field borders were established on two farms. Each border was planted with a native warm season
grass (NWSG) mixture that includes Indian Grass (Sorghastrum nutans), Little Bluestem (Schizachyrium scoparium), and Big Bluestem
(Andropogon gerardii). Other species that were common in the experimental plots include Johnson Grass (Sorghum halepense), Bermuda
Grass (Cynodon dactylon), Partridge Pea (Cassia fasciculata), Korean lespedeza (Lespedeza stipulacea), Curly Dock (Rumex crispus),
Common Ragweed (Ambrosia artemisiifolia), and Giant Ragweed (Ambrosia trifida). Four additional borders of varying widths (15m40m) were established with an identical vegetative treatment. Nineteen control field borders were selected in locations as similar as
possible to the treated borders, and represent traditional “ditch to ditch” farming techniques. Each plot was bordered on one side by a crop
field (e.g. Cotton (Gossypium sp.) and Soybean (Glycine sp.)) and on the other by riparian strip and wood line. Borders were established
and planted during the spring of 2002. The growth of the planted grasses was such that the borders contained mostly small emergent
vegetation during the breeding season of 2002, but was established by fall 2002.
Avian Surveys— Avian communities were surveyed during February and June using line transect methods (Buckland et al. 1993).
Transects were 200-m and were surveyed for 10 minutes between 6am and 10am (7am-11am in winter counts), weather permitting. All
individuals were identified and distance from observer estimated. To minimize the bias of extrinsic factors, analyses were restricted to
birds detected within 10-m borders for summer counts, and 10-m borders plus 30-m of the adjacent crop field for winter counts. Winter
counts included birds detected in the field, as it has been suggested that birds may forage near cover to reduce predation risk (Schneider
1984). Abundance and richness data of all field borders from the 2003 winter and 2002, 2003 summers were analyzed using ANOVA
(SYSTAT®) with field border treatment as the sole factor.
Productivity— An intensive nest searching/monitoring effort was conducted by a field crew throughout the breeding season (01 May to 01
August) of 2003. Every field border (treated and untreated) was thoroughly searched for nests of all bird species on a 7-10 day cycle.
Nests were monitored approximately every three days to determine nesting success in borders (Martin and Geupel 1993). Nest numbers
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1448-1458.
Fig. 3- Nest density related to field border width.
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Johnson, R.G. and S.A. Temple. 1990. Nest predation and brood parasitism of tallgrass prairie birds. J. Wildl. Management 54: 106-111.
Marcus, J.F., W.E. Palmer, and P.T. Bromley. 2000. The effects of farm field borders on overwintering sparrow densities. Wilson Bulletin 112: 517-523.
Martin, T.E. and G.R. Geupel. 1993. Nest-monitoring plots: methods for locating nests and monitoring success. J. Field Ornithol. 64: 507-519.
Puckett, K.M., W.E. Palmer, P.T. Bromley, J.R. Anderson, Jr., and T.L. Sharpe. 1995. Bobwhite nesting ecology and modern agriculture: field
examination with manipulation. Proc. Annu. Conf. Southeast. Assoc. Fish Wildlife Agencies 49: 507-517.
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Warner, R.E. 1994. Agricultural land use and grassland habitat in Illinois: future shock for Midwestern birds? Conservation Biology 8:147-156.
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Winter, M., D.H. Johnson, and J. Faaborg. 2000. Evidence for edge effects on multiple levels in tallgrass prairie. The Condor 102: 256-266.