Agricultural cropland constitutes most of the habitat available to wildlife in the Midwest. Some of these habitats have proven to be “ecological traps” for birds where productivity is well below levels necessary to sustain populations. Strip intercropping systems may improve habitat conditions for wildlife in agroecosystems. We evaluated bird use of experimental strip intercropping systems in 1992 and 1993 by observing bird behavior from tower blinds, censusing along transects, and searching for nests. Small-mammals were evaluated by using Sherman live-traps. Thirty-five bird species were observed with brown-headed cowbirds and vesper sparrows most abundant. Foraging was the most common bird behavior observed, and soybean and corn strips were preferred for use by birds. Four species of birds nested in strip intercropping systems, although only vesper sparrows nested in 1992. Only 2.4% of vesper sparrow nests successfully fledged young. Remaining nests were destroyed by cultivation or planting activities (39.0%), predators (29.3%), brown-headed cowbird parasitism (12.0%), weather (4.9%), desertion (4.9%), or observer error (2.4%). Two nests had unknown outcomes. Six small-mammal species were captured, although 94.3 % of all animals captured were deer mice. Deer mice prefer oat strips before oat harvest and soybean or corn strips after oat harvest. Bird species diversity and abundance is high in strip intercropping systems suggesting better foraging habitat than conventional row crop fields. These systems, however, provide ecological traps for birds by attracting them to nest in a poor production area. Small-mammal diversity in strip intercropping systems is low, although greater structural diversity in these systems might provide attractive small-mammal habitat for a greater period of the growing season than in conventional row crop fields.
1. Document bird and small-mammal abundance and species composition in an experimental strip intercropping system.
2. Determine preferential use of various crop strips by birds and small-mammals.
3. Assess avian nesting success and productivity in the strip intercropping system.
Bird species diversity and abundance is high in Iowa strip intercropping systems suggesting better foraging habitat than conventional row crop fields. Thirty-five bird species were observed with brown-headed cowbirds, vesper sparrows, red-winged blackbirds, and horned larks most abundant. Foraging was the most common bird behavior observed. Territorial behavior, pair-bond maintenance behavior, perching, preening, and nest maintenance behaviors were also observed. Soybean strips (40%) and corn strips (39%) were preferred for use by birds.
Strip intercropping systems provide ecological traps for nesting birds. More birds are attracted to nest in these systems than in conventional row crop fields, but avian productivity is as low or lower than in conventional fields. Four bird species nested in the strips, although only vesper sparrows nested in 1992. Forty-one vesper sparrow nests were found of which one fledged young. Remaining nests were destroyed by cultivation or planting activities (39.0%), predators (29.3%), brown-headed cowbird parasitism (12.0%), weather (4.9%), desertion (4.9%), or observer error (2.4%). Two nests had unknown outcomes. Sixty-one percent of vesper sparrow nests were parasitized by brown-headed cowbirds. One successful killdeer nest, one horned lark nest destroyed by weather, and one ring-necked pheasant nest with an unknown outcome were also found. Corn strips (50.0%) were preferred for use by nesting birds.
Small-mammal diversity is low in strip-intercropping systems, but greater structural diversity in these systems might provide attractive small-mammal habitat for a greater period of the growing season than in conventional row crop fields. Six small-mammal species were captured including deer mice (445 individuals), short-tailed shrews (16), thirteen-lined ground squirrels (4), house mice (3), eastern moles (3), and a norway rat. Deer mice prefer oat strips (58%) before oat harvest and soybean strips (47%) and corn strips (40%) after oat harvest.
Strip intercropping systems provide more attractive foraging habitat for birds than conventional row crop fields. If adopted on a wide scale, strip intercropping systems could potentially boost population levels of many bird species. Population levels of bird species that routinely nest in agricultural fields, however, would likely drop as a result of this change. Strip intercropping systems provide ecological traps for birds by attracting them to nest in a poor production area instead an area where nesting success is high. Deer mice populations would benefit from a wide spread adoption of strip intercropping systems because the systems provide cover and good foraging habitat for a longer period of the growing season than conventional row crop fields or conventional oat fields.
Forty percent of all nests found in strip intercropping systems were destroyed by farming implements. We recommend to farmers wishing to increase avian production on their land to reduce the number of times machinery passes through their fields. Waiting at least one month between passes through the field will also benefit many nesting species.
Educational & Outreach Activities
The findings of this research will be made available to both technical and lay audiences by making oral presentations and preparing publications.
-Annual Midwest Fish and Wildlife Conference – audience primarily wildlife ecologists and managers.
-Annual Conference for the Leopold Center for Sustainable Agriculture – audience a mixture of farmers, scientists, and lay people.
-Annual Meeting of the Crop Issues Team – Leopold Center for Sustainable Agriculture – audience a mixture of farmers and scientists.
-Practical Farmers of Iowa Field Day Tours – audience primarily farmers.
-Technical material will be submitted for publication in The Journal of Wildlife Management or The Wildlife Society Bulletin.
-The research findings will be provided to the Department of Animal Ecology wildlife extension specialist for publication in the Iowa State University Extension series on Managing Iowa Habitats.
Areas needing additional study
Very little is known about the effect sustainable agriculture systems and techniques have on birds and other wildlife. Only a few systems such as no-till corn and soybean production and strip intercropping systems have been studied. Research on wildlife use is needed in all areas of sustainable agriculture if we are to achieve better compatibility between production agriculture and wildlife conservation.