Grazing intensity effects on the breeding avifauna of North Dakota native grasslands

A breeding bird census and plant survey was conducted on 180 samples of lightly, moderately, and heavily grazed and hayed native grasslands in North Dakota in 1974. The ten most important cover plants on each of eight major physiographic landforms in three of the four regions (the Agassiz Lake Plain excluded) overlapped so extensively that only 19 species were involved: 13 grasses or sedges, four forbs, one shrub, and one clubmoss. Bird densities were generally highest in (i) regions and landforms containing numerous natural basin wetlands, (ii) flatter, glaciated landforms containing more fertile soils, and (iii) landforms of greater relief and high habitat heterogeneity. Avian species richness tended to decrease with increased grazing intensity, but total bird density increased due to higher populations of a few species, and hayland that had been mowed and raked during the previous growing season was highly attractive to some species.