Effects of grassland biomass harvest on nesting pheasants and ducks

Grasslands enrolled in conservation programs provide important habitat for nesting game birds and waterfowl, but conservation grasslands have been targeted as a source of biomass for bioenergy and this could impact nesting birds. We studied the effects of biomass harvest on nest success and density using 109 blue-winged teal (Anas discors), mallard (Anas platyrhynchos), and ring-necked pheasant (Phasianus colchicus) nests found in southwestern Minnesota during 2009 (pretreatment) and 2010 (posttreatment). Grassland biomass was harvested in late autumn of 2009 with production-scale machinery. Harvest treatments included controls (0% biomass removal), partial harvest (50 or 75% biomass removal), and full harvest (100% biomass removal) from 8 ha plots. Nest success averaged 31% and was not influenced by biomass harvest. Daily survival rates were greater for nests located closer to wetlands. Estimated total nest density (0.42 nests ha^-1; corrected for survivorship) was similar across harvest treatments, but within-plot analysis revealed nest density was greater in unharvested refuge regions. Estimated nest density was positively correlated with vegetation height and the spatial extent of wetlands surrounding each plot. Harvesting relatively small-scale patches of conservation grasslands in late autumn does not appear to be detrimental to nesting ducks and pheasants the following spring, but managers should consider leaving unharvested refuges near wetlands when harvesting large continuous tracts.