Effects of Range Treatment With 2,4-D on Food Habits of Rodents

Abstract

The food habits of rodents inhabiting shrub grass and perennial forb ranges in western Colorado were investigated to determine the kinds and proportions of foods eaten, the effects of range treatment with 2,4—D on food habits, and the degree of competition for food among rodents inhabiting these ranges. Treated and control areas at each site were trapped periodically and estimates were made of plant coverage. A part of the stomach contents of each rodent was mounted on a slide and was examined with microscopes. The volume in percent of each food item was estimated and recorded. Deer mice exhibited a seasonal variation in diet. Their winter food was primarily seeds whereas arthropods made up a large part of the diet during the summer months. Cutworms comprised almost one—half of the food ingested during June. Male and female deer mice showed no difference in diet, but the diet of deer mice varied with age group. fugi were found in the stomachs of rodents, particularly during the fall months. Deer mice occasionally ingested parts of small mammals. Grass seeds comprised a larger proportion and forb and shrub seeds a smaller proportion of the diet of deer mice inhabiting areas treated with 2,4—D than that for untreated areas. The availability of these food items appeared to be responsible for these observed differences in diet. Least chipmunks ate a variety of arthropods, seeds, and leaves, and, like the deer mouse, exhibited seasonal variation in diet. Although there was no significant difference in diets on treated and control areas, the influence of the availability of certain seeds was evident. Range treatment with 2,4—D had no effect on the diet of montane voles. Leaves and stems of forbs and shrubs comprised a large part of the summer diet on both treated and control areas on Grand Mesa. Differences in diet with sex and age were observed. The greater abundance of montane voles on treated areas appears to be due to an increase in grass cover and not to an increase in available food. No competition for food was observed among deer mice, least chipmunks, and montane voles at the population levels sampled in this study.