Effects of twice-over rotation grazing on the relative abundances of grassland birds in the mixed-grass prairie region of southwestern Manitoba

Abstract

The mixed-grass prairie region of southwestern Manitoba is a hotspot for many endangered grassland birds. This region has been degraded to less than a quarter of its historical amount of mixed-grass prairie. Remaining prairie is primarily used for livestock grazing. The objective of this study was to evaluate the contribution of sustainable land management practices, such as rotational grazing, in the conservation of this region. In 2008 and 2009, I compared the abundances of grassland birds on two grazing regimes, twice-over rotation and season-long, to ungrazed fields. Bird surveys were done during the breeding season and were conducted using 100-m fixed-radius point-count plots. I determined the effects of treatment, landscape and vegetation characteristics on songbird abundances using generalized linear mixed models. Grassland birds selected grazed pastures over ungrazed fields in both years, and species richness of obligate grassland birds was significantly greater (α = 0.10) on season-long than twice-over pastures (β = 0.419, p = 0.032, in 2008 and β = 0.502, p = 0.043 in 2009). Season-long grazing may actually benefit grassland bird communities by creating somewhat temporally stable areas of high use and low use within the pasture. However, nesting success studies and long-term monitoring are necessary to further understand how twice-over rotation grazing systems contribute to the conservation of grassland birds in southwestern Manitoba.