BIRD ABUNDANCE AND NESTING IN CRP FIELDS AND CROPLAND IN THE MIDWEST - A REGIONAL APPROACH

We compared the abundance and nesting success of avian species in Cons ervation Reserve Program (CRP) fields during the summer with that in r owcrop fields over 5 years (1991-1995) for 6 midwestern states (Ind., la., Kans., Mich., Mo., and Nebr.). Field techniques were standardized in all states. CRP fields consisted of either perennial introduced gr asses and legumes (CP1) or perennial native grasses (CP2), and the pla nt species seeded in CRP fields differed within and among the states. Disturbances to CRP fields included mowing (partial or complete), appl ication of herbicides, and burning. The height, vertical density, and canopy coverage of vegetation in CRP fields were measured in each stat e; values for these measurements were particularly low in Kansas. Mean annual total bird abundance in CRP fields ranged from 4.9 to 29.3 bir ds/km of transect. The most abundant species on CRP fields differed am ong states but included red-winged blackbirds (Agelaius phoeniceus), g rasshopper sparrows (Ammodramus savannarum), and dickcissels (Spiza am ericana). Although the total number of bird species was similar in CRP and rowcrop fields across the region, bird abundance was 1.4-10.5 tim es greater in the former. Nests of 33 bird species were found in CRP f ields compared with only 10 species in rowcrop fields, and the number of nests found was 13.5 times greater in CRP fields. Nest success in C RP fields was 40% overall; predation was the greatest cause of nest fa ilure. Long-term farm set-aside programs that establish perennial gras s cover, such as the CRP, seem to provide many benefits for grassland birds, including several species for which conservation is a great con cern.