Effects of old world bluestem (Bothriochloa ischaemum) on food availability and avian community composition within the mixed-grass prairie.

摘要

Various grassland bird species have displayed population declines over the past 30 to 40 years, and interest in explaining possible causes for the declines has prompted numerous studies. Many of these studies have focused on changes in agricultural practices; few have evaluated possible effects of the presence of nonnative grasses in grasslands. The objective of our study was to determine the effects a nonnative grass, Old World bluestem (OWB; Bothriochloa ischaemum), might have on grassland bird species abundance and richness, and on bird food availability (arthropod biomass). Three pastures each of native range, expired Conservation Reserve Program (CRP), and OWB were sampled from May to July 2001 in Comanche County, Kansas. Bird abundance and species richness were assessed by using a point-count method along 3 transects in each pasture. Food availability was estimated by collecting arthropods along 10 transects in each pasture by sweep-netting. Results showed significantly lower bird abundance and species richness in OWB pastures than in native pastures. OWB pastures also had significantly less arthropod biomass than native pastures. Because food availability (arthropod biomass) was directly related to percent forb cover within fields and was mostly absent in OWB pastures, we contend these were the primary factors contributing to lower avian richness and abundance in OWB fields when compared to CRP and native pastures.