DOT Project Number:  90-00-LRTF-004, 119

Fiscal Year:  1990-1991

Award:  $5,286.00

Principal Investigator:  Martha Camp, Iowa State University; Louis B. Best, Iowa State University, lbbest@iastate.edu

Summary Report:

THE IMPORTANCE OF ROADSIDES TO NESTING BIRDS IN INTENSIVELY FARMED AREAS

Intensive row crop farming in the Midwest has eliminated much wildlife habitat; some remaining habitat exists in linear areas such as roadsides. To determine the importance of roadsides to nesting birds in intensively farmed areas, our study evaluated the abundance, nest densities and nesting success of birds in roadsides adjacent to row crop fields in central Iowa from May through August, 1990 and 1991.

Thirty-five bird species were seen in roadsides, compared with 26 species in row crop fields. Bird abundance was greater in roadsides than in row crop fields. Few birds showed a preference for roadsides with native–mix versus exotic grasses or for burned versus unburned roadsides, but the abundance of some birds was related to vegetation height and vertical density in roadsides. American robin, brown thrasher, brown-headed cowbird, and vesper sparrow abundance, as well as total bird abundance, were greater in 1990 than in 1991. Horned lark, brown-headed cowbird, vesper sparrow, and total bird abundance were greater in fields in 1990 than in 1991.

One hundred and twenty nests of 8 species were found in 34 roadsides (10.2 ha). Red-winged blackbird nest density was greatest in roadsides with tall, dense vegetation; vesper sparrow nests were most dense in areas of sparse vegetation. Gray partridge and ring-necked pheasant nest densities were greatest in roadsides with the most residue coverage. Red-winged blackbirds most often placed their nests in the bottom or in the fence of a roadside; all vesper sparrows nested in the short vegetation of the foreslope. Daily nest survival rates for the red-winged blackbird and for all species combined were 0.9471 and 0.9428, respectively. Fifty-five percent of redwing nests, and 52% of the nests of all species were destroyed by predation. Redwing nests placed in forbs, shrubs, and the fence were more successful than those built in grasses other than reed canarygrass.

Seeding native grasses and forbs in roadsides may increase the attractiveness of these areas to birds that use such substrates for nesting. Fences are used by some birds in place of vegetation for nest support and should be retained in roadsides. Prescribed burns carried out periodically in each roadside would increase the vigor and structural heterogeneity of roadside vegetation; mowing roadsides should be discouraged except at the roadside shoulder.