NESTING SUCCESS OF SONGBIRDS IN THE UPPER MISSISSIPPI RIVER BASIN, FLOODPLAIN AND UPLAND FORESTS Melinda G. Knutson , Randy K. Hines, Colin M. Sveum, and Carl E. Korschgen U.S. Geological Survey, Upper Mississippi Science Center, La Crosse, WI 54602. Continent-wide population declines have led to public concern over songbirds that summer in the U.S., but winter in Central and South America (neotropical migrant songbirds or NTMBs). Recent studies of forest-nesting NTMBs indicate that some species are experiencing reproductive failure in the agriculture-dominated regions of the Midwest. The major culprit seems to be forest fragmentation. Songbirds nesting in small forest patches experience high rates of nest predation and brown-headed cowbird (Molothrus ater) parasitism. Because of its geology and glacial history, our study area, the Driftless Area Ecoregion in the Upper Mississippi River basin, has larger forests than other parts of the agricultural Midwest. In addition, the large floodplain forests of the Upper Mississippi River have high songbird diversity and abundance and may be important in maintaining some songbird populations. Our goal is to compare NTMB reproductive success between uplands and floodplain forests and link nest outcomes with vegetation structure and landscape composition. Ten upland and ten floodplain plots have been followed since 1996. In 1997, 572 nests among 45 species were found, 294 nests in the floodplain and 278 nests in the uplands. Nest survival averaged 31-36%. There were no statistical differences in survival between upland and floodplain birds. More nests failed from predation than cowbird parasitism. Overall, 12% of nests were parasitized, but only 5% fledged a cowbird. No differences in parasitism between floodplains and uplands were found. Prothonotary warbler (Protonotaria citrea), American redstart (Setophaga ruticilla), American robin (Turdus migratorius), warbling vireo (Vireo gilvus), and yellow warbler (Dendroica petechia) nests were found primarily in floodplain forests. Three times more American redstart nests were found in floodplain forests than in upland forests (64 vs. 21, respectively). Acadian flycatcher (Empidonax virescens), rose-breasted grosbeak (Pheuticus ludovicianus), indigo bunting (Passerina cyanea), red-eyed vireo (Vireo olivaceus), ruby-throated hummingbird (Archilochus colubris), scarlet tanager (Piranga olivacea), ovenbird (Seiurus aurocapillus), and wood thrush (Catharus mustelinus) nests were found primarily in upland forests. Comparisons of our data with those of other published studies indicate that our study plots fall in an intermediate range of songbird productivity and could be important in maintaining population levels for some species. Additional data collection is necessary to understand year to year variation and increase our power to identify differences in nest success among habitat types. Keywords: songbird, neotropical migrant, Mississippi River, Driftless Area, forest Melinda G. Knutson USGS, Biological Resources Division Upper Mississippi Science Center 2630 Fanta Reed Rd, P.O. Box 818 La Crosse, WI 54602-0818 UMSC home page: http://www.emtc.nbs.gov/umschome.html melinda_knutson@usgs.gov 608-783-6451 FAX 608-783-6066 Platform