| Grassland birds are of conservation concern because of population declines, habitat loss and habitat degradation. Grassland reserves are increasingly important for managing several species. Design proposals assume agriculture is an appropriate landscape context for these conservation areas. However, grassland/agriculture interactions are poorly understood. Agriculture may provide foraging resources and alter predator distribution and abundance, modifying reproductive success of grassland birds.; To assess the effects of grassland-agriculture edges on nesting success, I monitored 1,153 nests of Dickcissels (Spiza americana), Field Sparrows (Spizelia pusilla), Eastern Meadowlarks ( Sturnella magna), and Red-winged Blackbirds (Agelaius phoenicus ), 1996--2000. Only Field Sparrows were parasitized by Brown-headed Cowbirds (Molothrus ater), and all parasitized nests were within 50 m of a wooded edge. Distance to agricultural and wooded edges and grassland patch size did not significantly influence nest predation.; Beyond natural agents, haying and mowing destroy many nests, and Dickcissels are especially harmed by these disturbances. Temporal variation in nest productivity can greatly affect a species' ability to overcome losses through replacement nesting. I found predation rates of Dickcissel nests varied within seasons, but did not increase or decrease. Concomitant with a seasonal decrease in clutch size was increasing nestling survival, resulting in similar nest productivity throughout breeding seasons.; I used radio telemetry to measure seasonal fecundity, renesting behavior, and habitat use of female Dickcissels. Almost all females that remained within the study area fledged young. However, most birds emigrated in response to nest failures. Replacement nests were initiated soon after failures at sites with similar vegetation characteristics. Dickcissels used the agricultural matrix differently with respect to nesting stage. During incubation, few females used cropland. In contrast, most females with nestlings and fledglings frequently used cropland.; Agriculture is an appropriate landscape context for grassland reserves. I found agricultural edges do not influence nest predation, reserves in agricultural settings support successful nesting throughout breeding seasons, and cropland is an important foraging habitat for birds provisioning nestlings and fledglings. |
