Development of a Grassland Integrity Index Based on Breeding Bird Assemblages |
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Authors: | Bryan R Coppedge David M Engle Ronald E Masters Mark S Gregory |
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Institution: | (1) Rangeland Ecology and Management, Division of Agricultural Sciences and Natural Resources, 368 Agricultural Hall Oklahoma State University, Stillwater, Oklahoma 74078, USA;(2) Tall Timbers Research Station, Tallahassee, Florida |
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Abstract: | We utilized landscape and breeding bird assemblage data from three Breeding Bird Survey (BBS) routes sampled from 1965–1995
to develop and test a grassland integrity index (GII) in a mixed-grass prairie area of Oklahoma. The overall study region
is extensively fragmented from long-term agricultural activity, and native habitat remnants have been degraded by recent encroachment
of woody vegetation, namely eastern redcedar (Juniperus virginiana L.). The 50 individual bird survey points along the BBS routes, known as stops, were used as sample sites. Our process first
focused on developing a grassland disturbance index (GDI) as a measure of cumulative landscape disturbances for these sites.
The GDI was based on five key landscape variables identified in an earlier species-level study of long-term avian community
dynamics: total tree, shrub, and herbaceous vegetation cover indices, overall mean landscape patch size, and grassland patch
core size. The GII was then developed based on breeding bird assemblage data. Assemblages were based on commonly used response
guilds reflective of five avian life history parameters: foraging mode/location, nesting location, habitat specificity, migratory
pattern, and dietary guild. We tested the response of 78 candidate assemblage metrics to the GDI, and eliminated those with
no or poor response or with high correlations (redundant), resulting in 13 metrics for use in the final index. Individual
metric scores were scaled to fall between 0 and 10, and the cumulative index to range from 0 to 100. Although broader application
and refinement are possible, the avian-based GII has an advantage over labor-intensive, habitat-based monitoring in that the
GII is derived from readily available long-term BBS data. Therefore, the GII shows promise as an inexpensive tool that could
easily be applied over other areas to monitor changes in regional grassland conditions. |
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Keywords: | avian assemblages Conservation Reserve Program fragmentation grasslands juniper landscape pattern Oklahoma response guilds |
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