(1) Differences in meadow vole population densities were attributed to nutrient treatment effects on habitat quality; densities were low in communities with low plant species diversity and poor ground cover. (2) Survivorship was decreased in wheat field fertilized treatments, apparently due to poor vole habitat quality, although net primary production was significantly increased. (3) There was no evidence of toxic effects of sludge on vole population density, survival, or reproductive parameters. (4) Sex ratios favoured females in high food-quality habitats and males in low food-quality habitats.