Response of Riparian Avifauna to Percentage and Pattern of Woody Cover in an Agricultural Landscape

To better understand bird response to percentage and pattern of woody cover in agricultural areas, we recorded richness and abundance of breeding birds in 500-m transects along 18 wooded streams in southeastern Nebraska. Transects had differing amounts of woody cover in the surrounding landscape (∼2-39%) out to distances of 500, 1,000, and 2,000 m. We grouped bird species as woodland (22 species) or edge (30 species) and analyzed results from the 1999 and 2000 breeding seasons using information theoretic methods. Richness of the woodland group increased with percentage of woody cover out to 500 m, but abundance did not change. In contrast, richness of the edge group was not affected by landscape variables, but abundance increased as percentage of woody cover decreased out to 1,000 m. Eight species increased in abundance and 5 decreased with increasing percentage of woody cover in the landscape out to distances of 500, 1,000, or 2,000 m. The great crested flycatcher (Myiarchus crinitus) was not present at sites with ≤14.7% woody cover in the surrounding landscape out to 500 m, and the eastern woodpewee (Contopus virens), except for one site, was not present at sites with ≤24% woody cover out to 500 m. The Baltimore oriole (Icterus galbula) and warbling vireo (Vireo gilvus) apparently responded to the presence of large eastern cottonwood (Populus deltoides) trees. Management for a diverse avifauna in fragmented agricultural landscapes should include both local- and landscape-scale variables, including the amoung and pattern of woody cover in the surrounding landscape.