Investigating the Effects of Bison Grazing on Grassland Songbirds

Abstract

The National Bison Range (NBR) in the Mission Valley of Montana manages a herd of 325-350 bison (Bison bison).  Bison are rotated through eight grazing pastures, which consist mostly of intermountain grassland.  This creates different grazing intensities, based on length of time grazed, season grazed, and density of bison. Grazing is considered to be an important source of disturbance in grassland systems. However, different grazing intensities may create more or less favorable conditions for grassland breeding songbirds, a suite of birds that has declined drastically over the last few decades. This research investigates the interaction between bison grazing and songbird abundance. We used double-dependent observer transects to record grassland songbird observations during the pilot season of 2015. We present preliminary results from the pilot season of grassland songbird abundance and density. The outcomes will culminate into a concrete, local monitoring program for the NBR to support conservation of grassland songbirds, and will allow them to adjust management activities to maintain suitable grassland songbird habitat.  Furthermore, the research will illuminate the relationship between a native grazer and grassland birds. While domestic livestock have largely replaced native grazers on grasslands, numerous reintroduction efforts of bison have been proposed.  This study will help inform the expected outcomes and management objectives of those reintroduction efforts.