What Characteristics of Shelterbelts are Important to Breeding Success and Return Rate of Birds?

Abstract

-My field assistants and I studied breeding bird populations in 16 sites made up of shelterbelts and four sites including sections of woody draws in S-central North Dakota from 1985-1989. We documented a total of 42 species of birds nesting in wooded habitat on the study area. The composition of breeding bird species in shelterbelts was similar but not identical to that in the woody draws (23 of 42 species nested in both habitats). Breeding bird communities in these shelterbelt sites were more similar to those of local woody draws than they were to communities of previously studied woody draws in western North Dakota and of shelterbelts in Minnesota. I used logistic regression to examine the relationships between landscape-level and macrohabitat characteristics of shelterbelt sites such as isolation, area and grazing status of a site and the nesting success and return rates of three common breeding species of migratory songbirds (American robin, Turdus migratorius; brown thrasher, Toxostoma rufum, and loggerhead shrike, Lanius ludovicianus). Sites ranged in size from 0.3 to 3.4 ha and ranged in isolation from other wooded habitat from <0.1 to 1.6 km. Five of the 15 intensively studied sites were regularly grazed by livestock. Nesting success of brown thrashers was significantly higher in more isolated sites (P < 0.001). Thrashers were also significantly more likely to return to breed again to more isolated sites (P < 0.04) and to grazed sites (P < 0.002). These results should caution against uncritical support for construction of dispersal corridors.