- Takos, Michael James
Pennsylvania State College
A field study was made of some of the interrelationships of a muskrat population and its plant environment on a limited area of marsh island in Central Maine. The plant life was studied by means of permanent list quadrats which were established in three plant types. The relative abundance of the species of plants occurring on the quadrats was determined by a modification of Raunkiaer's method of frequency, and the index of availability for each plant for the entire marsh was calculated from the frequency data. An index, called the forage ratio, was derived which expressed the relationship of the kinds and amounts of plants available in the marsh to the kinds and quantities eaten by muskrats. Data on the food habitats of the muskrat were obtained from observation of scraps left at feeding platforms. Records of the plant species found, the parts eaten, and of the plant type location were made for each feeding platform. The frequency of occurrence of the various plant species eaten was calculated by feeding periods, and by ten-day intervals throughout the growing season. The relation of phenological phenomena to muskrat feeding habits was also observed.
Muskrat food habits were found to be governed by many complex factors, among which are: palatability, availability, water levels, phenological phenomena, home range of the animals, and overhead cover. Some damage to waterfowl food plants was found even when other food plants were abundant. However, most of the plants eaten by the muskrats were not important foods of waterfowl in Maine. Wild rice was the only important food of waterfowl eaten in appreciable amounts by the muskrats on the area studied. Observations made on nearby areas, however, indicate that other species of waterfowl food plants are eaten extensively under certain conditions. Muskrat damage to the stands of marsh plants was observed but most of the damage was slight and had a tendency to repair itself. An exception to this was seen in the case of wild rise. Water level fluctuations were the most inimical factor operating against the vegetation of the area studied. A dry season was the primary cause of the low water levels, but conditions were aggravated by man through demands for water power. Although a total of thirty-three plant items was recorded as being consumed by the muskrats, the species found to be of the greatest importance to the animals on the study area were: cattail (Typha latifolia), sweet flag (Acorus Calamus), wild rice (Zizania aquatoin), sedge (Carex lacustria), and the arrowleafs (Sagittaria latifolia and S. cuneata). It is believed that further research on the relationships between the muskrat and its plant environment over a wider range of habitats is essential before extensive plans for the management of the animal can be established.