Effects of rotational grazing on grassland songbirds on U.S. Dairy farms.

Abstract

Dairy pastures and hayfields provide important habitat for several grassland bird species of conservation concern, and farm management can have a substantial impact on populations of these species. Understanding the value of rotational grazing to grassland birds may reveal new opportunities for bird conservation, and may clarify the degree to which this management practice can enhance agricultural sustainability. We evaluated management practices (e.g. grazing intensity) and habitat variables (e.g. land cover) at 100m and 1200m radii on 53 dairy farms in Wisconsin, Pennsylvania and New York, in order to assess whether rotational grazing farms supported substantially higher abundances of three grassland bird species – Savannah Sparrow, Bobolink, and Grasshopper Sparrow -- than other dairy farms. We conducted 2-way ANOVAs in SAS (9.2) to examine differences in relative abundance among states and farm types using PROC GENMOD. Additionally, we modeled relative abundance as a response to Julian date and land cover at 100m and 1200m radii using PROC GLIMMIX. Abundances of each grassland bird species did not differ significantly among farm types. Responses to land-cover variables differed among species but demonstrated that relative abundance was positively associated with the proportion of hayfields and pastures in the surrounding landscape, and negatively associated with woody cover. Savannah Sparrows and Grasshopper Sparrows each showed a significant response to at least one habitat variable at the 1200m scale. Our results suggest that differences in abundance of grassland birds among farm types are modest at best, and that the impact of management practices on these species must be understood in the context of the surrounding landscape. Our data show that grassland birds can benefit from increases in the total area of pasture and hayfields on the landscape, which could be provided through broad adoption of rotational grazing. However, the benefits provided by increasing grassland habitats on a small number of farms are unlikely to have a substantial impact on bird populations, particularly in the context of a highly fragmented agricultural landscape. Future research for conservation planning and policy development should focus on the landscape scale (i.e. ! 500 ha) to ensure that conservation actions are most effective.