Responses of songbirds and small mammals to harvests of native grasslands for biofuels in Western Minnesota

Abstract

Some grassland birds and small mammals exhibit changes in abundance following vegetation removal in the previous year, but it is unknown to what extent these organisms respond to harvests of diverse, native grasslands. This thesis examines the effects of harvesting such grasslands on songbirds and small mammals, representing an important step in evaluating the conservation value of grasslands used for biofuel harvest. I analyzed abundance data collected from area-based bird surveys in grassland biofuel plots harvested via different pattern and percentage in western Minnesota, USA, from 2009 to 2013 (Chapter 1). Small mammal trapping was conducted in the same plots from 2009 to 2012, and abundance and occupancy data collected from these surveys was also analyzed (Chapter 2). I estimated relative abundance of 11 species of grassland birds and 7 species/genera of small mammals among the different harvest intensities and years of study. Four bird species and species richness showed declines in abundance following harvests, whereas two species showed increases in abundance. Harvests also resulted in negative impacts on two small mammals. The removal of vegetation in fall results in shorter, less dense vegetation the following spring, which creates largely unsuitable habitat for tall-grass songbirds (e.g., sedge wren) but more optimal habitat for species that prefer shorter vegetation (e.g., grasshopper sparrow). Additionally, the reduction in ground litter is detrimental to small mammals that prefer thicker vegetation (e.g., voles of the genus Microtus). At the community level, harvesting native grasslands appears to have little impact on grassland birds and small mammals, but it is nonetheless important to identify what species are present prior to harvesting so that harvesting activities do not result in detriment to these species.