Changes in habitat and in quality of food intake after a summer of grazing by fenced voles (Microtus pennsylvanicus)

Nutritional components of individual plant species such as protein, nonstructural car bohydrates, neutral detergent fibers and total phenolics are commonly used to assess the quality of vole habitats and food selection. Although voles act individually on each plant species of their habitat, I question the use of such variables for following habitat manipulation by this small herbivore after a summer of grazing. I tested the reliability of using chemical analyses of green biomass from quadrat samples, and fecal matter of meadow voles (Microtus pennsylvanicus) for determining changes in habitat quality and food quality by confined animals. Voles were introduced into fenced plots during early summer and reached peak numbers of 350 animals/ha. Green biomass did not vary among the grazed plots, nor between grazed and ungrazed (control) plots after a summer of grazing activity. Chemical components of green biomass did not differ sig nificantly between grazed and ungrazed plots. As a whole, green biomass samples were unreliable for detecting habitat quality changes after vole grazing. Food habit determina tions from fecal remains showed that five herbaceous species were selected by confined voles. Moreover, fecal matter contained significantly more carbohydrates, total phenohcs, and neutral detergent fibers in the heavily grazed plot compared with samples collected in lightly grazed areas, indicating that consequences of heavy grazing could be detected from such analyses. I conclude that chemical analyses of fecal matter rather than green biomass represent a better way of measuring out changes in food quality of vole habitats. Further studies are needed to know which categories of animals make up the fecal drop ping samples in the field, and how much information is lost when samples are collected directly from animals or on bi-weekly or monthly schedules from dropping boards.