A Landscape Approach to Grassland Bird Conservation
The Grassland Bird Conservation Area model is a conceptual model based on broadscale landscape characteristics thought to be desirable for a variety of grassland nesting birds. Although it has proved useful for conservation planning, empirical models of species specific habitat and landscape attributes can further refine planning efforts. Breeding Bird Survey data can be used to explore some aspects landscape scale habitat selection, but these data were not collected for this purpose and many assumptions must be made when developing models from these data. A better approach is to develop a study specifically designed to link bird densities with local and landscape habitat attributes.
Dr. Dave Naugle ( University of Montana ) and Dr. Rolf Koford ( Iowa State University ) have initiated a large, multi-state and multi-partner study to examine grassland bird habitat selection in the Prairie Pothole Region of the U.S. U.S. Fish and Wildlife Service Regions 3 and 6 HAPET offices provided technical assistance by drawing point count samples based on landscape and land use characteristics.
Landscape models for grassland birds were based on point count data collected in June 2003-2005 by and under the direction of Frank Quamen (PhD student), Dave Naugle (major professor, Montana State University), Shane Patterson (MS student) and Rolf Koford (Iowa State University). A stratified random sample was drawn each year based on the amount of grass in the landscape, cover type (grass (70% of points), hay (15%), crop (15%)), and by seven wetland management districts to distribute the sample across the prairie pothole region of Minnesota and Iowa.
The number of detections was large enough to produce models for Sedge Wren, Clay-colored Sparrow, Grasshopper Sparrow, LeConte’s Sparrow, Savannah Sparrow, Bobolink, Dicksissel, and Western Meadowlark. A variety of regression methods were used to model bird density (bird detections/ha). For each species, the best model was selected using information theoretic selection methods (i.e., AIC, BIC).
Models were mapped by applying regression equations to grids of percent cover and BBS relative abundance (used as a spatial covariate to account for species range), and limited to grass areas >1 ha. For models that predicted the number of pairs, the total number of pairs per 40 acres was predicted by calculating the pairs predicted for the grass portion of each 40 acre cell. Maps were ‘smoothed’ by taking the average predicted pairs in a 40 ac cell for a 1-mile radius. Although species models differed by landscape scale and specific landscape variables, the resulting maps were similar. To summarize and simplify, the total predicted number of pairs was summed for Sedge Wren, Grasshopper Sparrow, LeConte’s Sparrow, Savannah Sparrow, Bobolink, and Dicksissel. Clay-colored Sparrows were not included because of numerical issues in estimating the model (see Quamen 2007); Western Meadowlark were not included because the logistic regression model used predicts probability of presence, not number of pairs. Because all species models improved with the inclusion of local variables, landscape models depict the potential for breeding pairs where suitable local habitat exists.
Citation: Quamen, F. R. 2007. A landscape approach to grassland bird conservation in the prairie pothole region of the northern great plains. Dissertation, University of Montana, Missoula.
For additional information about grassland birds contact:
Region 7 Inventory and Monitoring Coordinator
U.S. Fish and Wildlife Service
1011 East Tudor Road
Anchorage, AK 99503