Cooperative Fish and Wildlife Research Units Program: Iowa
Education, Research and Technical Assistance for Managing Our Natural Resources

The Spring Run Wetland Complex of northwest Iowa is one of the largest grassland units in the state. It has been recognized as an official site in the National Audubon Society's Important Bird Areas program. Previous research indicated that increased vegetation diversity could enhance the reproductive success of grassland birds. Our objectives are to (1) quantify bird use of four habitat types that have been or might be established on managed land in the Spring Run Complex, (2) monitor vegetation composition and structure in each habitat, (3) estimate nest success, nestling growth rate, and other aspects of habitat quality for common bird species using each habitat type, and (4) measure invertebrate populations in the three habitat types The Spring Run study area includes 24 study fields arranged in a complete block design (six blocks each with four field types). The four field types are (1) Cool Season - introduced grasses, (2) New CP-2 - a mix of native tall-grass species planted since 2000, (3) Old CP-2 - a mix of native tall-grass species planted before 2000, and (4) Primo - a diverse mixture over 40 species of forbs and native grasses. In the summer of 2008, we conducted seven rounds of line transect bird surveys on each field. We detected 2,788-3,280 individuals of 28-38 different species during the 2007-2008 surveys. The most common species were Bobolink, Common Yellowthroat, Grasshopper Sparrow, Red-winged Blackbird, and Sedge Wren. We conducted nest searches for grassland songbirds on all fields using systematic searches and behavioral observations. We found a total of 109-152 nests of 9-11 different species in 2007-2008. We found more nests in 2008 than in 2007 (109) but we found 2 fewer species in 2008. In addition to determining nest fates, Red-winged Blackbird, Dickcissel, and Bobolink nests were monitored to assess nestling growth rates and baseline corticosterone levels. Corticosterone levels are good indicators of physiological conditions of developing birds; increased corticosterone levels are associated with poor feeding conditions. During 2008, we measured 66 Red-winged Blackbird nestlings, 5 Bobolink nestlings, and 4 Brown-headed Cowbird nestlings. During 2008, we took blood samples from 24 birds just prior to fledging. Blood glucose readings were taken in the field from each nestling using a portable blood glucose meter. Blood samples were centrifuged and stored at Iowa Lakeside Laboratory until the end of the summer. Nestling growth measurements and blood samples were collected using the same field methods in 2009. During 2009, we took blood samples from 66 nestlings. We conducted 2 rounds of vegetation surveys and 3 rounds of invertebrate sweep net surveys during 2008. Invertebrate sweep net samples collected during 2008 are being idetified to order, dried and weighed. Vegetation data from 2007 and 2008 have been summarized. We conducted vegetation and invertebrate samples using the same field methods during 2009.