Water vole

“ Under such conditions many voles appear to be undernourished, and some are actually emaciated. Dehydration may be an important factor at times when dew is unavailable for drinking and the green vegetation remaining is exceptionally low in moisture content. Voles caught at such times and brought to the laboratory, drank avidly, and gained several grams soon after being offered water or succulence. Cannibalism by adults on newborn young in times of drought may be motivated by the acute need for moisture and nutritious food. In times of drought the birth rate is at low ebb. ”

“ A shortening of the tail is seen in the voles, to which the common meadow mice of various species belong, and still more in the lemmings, in the Old World mole rats, and in our pouched gophers. All these are not only ground-keeping kinds, but burrowers, and have no use for a long tail, save in the case of the muskrat, which is really a big vole that has taken to an aquatic life, and needs an oar to scull himself through the water; for muskrats swim more by means of their tails than by their feet. ”

“ In the region of my study the prairie vole breeds the year round, but the rate of breeding changes continually. There is no regularity in the trend of the breeding season from year to year. It is obvious that the species is responsive to environmental changes and is so well attuned that its breeding is speedily initiated or inhibited by changes to favorable or unfavorable weather. The incidence of breeding is highest when temperature is moderate and both water and foods of preferred sorts are plentiful. ”

“ Severe fighting between adult prairie voles occurs at times. Occasionally, sharp squeaks accompanied by brisk rustling in the grass suggesting pursuit or conflict, are heard in their habitat. An unusually large adult male, long resident on a study area, suddenly lost weight and deteriorated in condition over a period of several days, then was found dead in a nest-box attached to a trap. Dissection revealed numerous punctures in the skin and flesh of the neck and back, probably made by the incisors of another vole. ”

“ As many as five adults have been caught in a trap simultaneously at times when the population density was high. At such times, the meadow habitat is crossed by a maze of interconnecting surface runways and one runway may be traced continuously for 100 yards or more. Because each individual vole normally confines its activity to a small area, only a fraction of an acre, it is evident that individuals living at different places overlap in their home ranges, and also in the trailways followed in foraging. ”

“ Predation by the long-eared owl was especially heavy; remains of voles were identified in 72 per cent of its pellets examined. Korschgen (1952:39) found remains of voles in 70 per cent of 704 pellets of the long-eared owl. The reason for the heavy diet of Microtus seems to be that both the owl and the vole are especially active at dusk. A group of long-eared owls, living near the edge of Quarry Field, probably exerted an influence on the density of the local population of voles because of the high ratio of predator to prey animals. ”

“ Scarcely had he recovered sufficient coolness to look about him, when the object of his terror emerged with dripping jaws, and he was enabled, for the first time, to form an opinion of the arch-enemy of vole-kind.
To avoid the bird of prey, a vole need only remain below the surface; to avoid the little gentleman in black, he need only rise above it; but from the grim pursuit of the weasel, bent on meal or murder, there is no escape. ”

“ Under the roots a pair of voles have annually brought forth several young families; and yet perfect amity seems to exist between the birds and the rodents. We have seen the eggs lying for hours uncovered and unprotected, and at other times the young birds, not more than a few hours old, swimming about in the water when the voles were constantly feeding, crossing and recrossing from bank to bank. If voles were addicted to killing birds the downy young of the moorhen would have afforded tender morsels, and have been easily obtained in a small confined pool ere they were able to take wing. ”

“ Nine other species of small mammals occur in the same habitat with the prairie vole, and frequently use its runways. The vole makes a network of paths through the grass, and constructs its own burrows which lead to its nests and food stores. Each of fifteen nests found were underground. Most, if not all, of the underground tunnels are dug when the soil is moist, not when the soil is dry.
The commonest flea on the prairie vole is Ctenophthalmus pseudagyrtes; it averages 1.9 (for subadult voles) to 3.4 (for adult voles) per individual vole. ”

“ The cuttings that have accumulated at the base of the plant may be eaten, but frequently they remain as evidence of the vole's feeding activity.
On May 12, 1946, an analysis was made of the cuttings found in an area of alfalfa, grasses, and weeds. From table 1 it may be seen that quackgrass, alfalfa, wild lettuce, and cleavers were common. In three nights 70 traps caught 8 prairie voles and 3 deer mice; no pine mice or cotton rats were caught on the area. The stomachs of the voles and the deer mice were examined, and only the stomachs of the voles contained green material. ”

“ For example, bait acceptance is better in the winter when natural foods, especially greens, are scarce, with the result that a higher catch can be made with the same population density. Interference with the trap line by other animals also affected the catch of voles. In warm weather the traps were checked in both morning and evening, and the catch was correspondingly greater than it was in cool weather when the traps were checked only once daily. The ratios obtained of young to adult voles cannot be accepted at face value as the true ratios in the population, either. ”

“ The Voles are allied to the preceding groups, but are marked externally by a shorter and heavier form than the typical rats and mice. Their ears are shorter, their noses blunter, their eyes smaller, and the tail generally shorter. They are found in great numbers at certain seasons, when {158}they often develop into a pest. The Short-tailed Field-vole is responsible for much destruction of crops in Europe. One of the latest plagues of these animals took place in the Lowlands of Scotland, where these voles devoured all the higher pastures on the hills. ”

“ Although voles were a common item of prey for many species of predators on the Reservation, no marked effect on the density of the population of this vole could be attributed to predation pressure. Only when densities reached a point that caused many voles to expose themselves abnormally could they be heavily preyed upon. ”

“ The rattlesnakes probably were less important as predators on voles than on other small mammals more common in the usual habitat of these snakes. The blue racer (Coluber constrictor) was common in grassland situations on the Reservation (Fitch, 1952:24) and twice was observed in the role of a predator on voles; one small blue racer entered a live-trap in pursuit of a vole and another blue racer was observed holding a captured vole in its mouth. The blue racer seems well adapted to hunt voles and probably preys on them extensively. ”

“ The mean number of embryos per female was higher than the mean number of young per litter delivered in captivity and the mean number of young per litter delivered in traps was lower than in those delivered in captivity. The differences were not statistically significant. In some instances females that delivered young voles in traps may have delivered others prior to entering the trap or the mother or her trapmates may have eaten some of the newborn voles before they were discovered. ”

“ But he became the wisest, shyest, most watchful vole along the wooded river-reach, and in time his neighbours and offspring were so influenced by his example and training that a strangely furtive kindred, the wildest of the wild, living in secrecy—their presence revealed to loitering anglers only by tell-tale footprints on the wet sand when the torrent dwindled after a flood—seemed to have come to haunt the river bank between the cottage gardens and the swinging bridge above the pool where Brighteye dwelt. ”

“ Those traps set in spots where there was little vegetation other than the dominant grass caught fewer voles than traps set in spots with a more varied cover. Poa pratensis formed an understory over most of the area studied, especially on House Field, and attained local dominance in shaded spots on both fields. The higher basal cover provided by the Poa understory seemed to support a vole population larger than those that occurred in areas lacking the bluegrass. Disturbed situations, such as roadsides, were characterized by the dominance of Bromus japonicus. ”

“ The minute weasel is on the track of a vole or a wood-mouse and cannot harm the birds. Yes, he can take the nestlings from the robin's and willow-wren's nests, and from other nests built on the ground, but what has the chaffinch to do with it all? Can it be that there is some fatal weakness in birds, in spite of their wings, in this bird especially, such as exists in voles, and mice, and rabbits, and in frogs and lizards, which brings them down to destruction, and of which they are in some way conscious? ”

“ The flood in 1951 reduced the population of voles and obscured the normal seasonal trends. Although House Field produced a heavier crop of vegetation, Quarry Field produced a larger crop of rodents, chiefly Microtus and Sigmodon. In House Field, however, the ratio of Sigmodon to Microtus was notably higher. Presumably the cotton rats competed with the voles and exerted a depressing effect on their numbers. The intensity of the effect seemed to depend on the abundance of both species. ”

“ Some fleas have a habitat preference as well as a host specificity. As voles from different areas were examined, different kinds of fleas were encountered. A population of free-living voles under observation on the Campus at Lawrence was parasitized only by Ctenophthalmus pseudagyrtes. From 90 prairie voles collected in a field of clover 4 miles northwest of Lawrence, the only species of flea recovered was Orchopeas leucopus. ”

“ No intolerance of other voles exists and, in laboratory cages, groups of voles lived together peaceably from the time they are placed together. Crowding does not seem to be harmful directly, therefore, and high densities will develop if food and cover resources permit. ”

“ The causative factor directly influences the population either by inhibiting reproduction or by increasing infant and prenatal mortality. The net reduction is due to an inadequate replacement of those voles lost by normal attrition.
Most voles, under natural conditions, live less than one year. Those individuals born in the autumn live longer, as a group, than those born at any other time. Since the heaviest mortality is in young voles, adults which become established in an area may live more than 18 months and, if they are females, may produce more than a dozen litters. ”

“ It has been asserted that voles feed upon flesh when opportunity offers, but perhaps we cannot better vindicate their general character in this respect than by relating an incident which has occurred annually for some years past. In a quiet pool known to us, a couple of moorhens have annually hatched and reared one or more broods under the shadow of an old thorn-tree, the nest being interwoven with one of the lower boughs which floats on the surface of the water. ”

“ This grooming may have some significance as a search for ectoparasites such as fleas, or mites that often infest the voles. However, after prolonged grooming by a companion, a vole's fur was of mussed and disarranged appearance. Although the grooming that occurs between voles that are resting in nests seems to have no direct significance as sexual behavior, somewhat similar actions constitute part of the mating pattern. A sexually aroused male overtaking a receptive female, slides his chin forward along her back with jerky, stroking movements. ”

“ Voles, living in clover and alfalfa, do not make runways as distinct as they do in grasslands. The clover and alfalfa plants are branched and of a spreading growth form, whereas the grasses have leaves which are appressed to the main stem. The individual grass plants grow close together, and a vole cannot run through grass without trampling some of it. As voles use the same paths repeatedly, the grass in their runs becomes flattened and dies. There is sufficient room between the stems of the clover and alfalfa plants to allow the voles to pass through without treading on the stems. ”

“ Though the young voles, in the tunnelled buttress of the river-bank, lived under the care of experienced parents ever ready and resolute in their defence, and became as shy and furtive as the wood-mice dwelling in the hollows of the hedge beside the pond, they were not always favoured by fortune. The weakling of the family died of disease; another of the youngsters, foraging alone in the wood, was killed by a bloodthirsty weasel ”

“ Cannibalism, involving destruction of the newborn, is probably an important factor in the population dynamics of the prairie vole. Only a small percentage of the young known to have been born on an area ever survived to be live-trapped; this small percentage was indirect evidence of decimating losses in the young. Under unfavorable conditions each of several females killed and ate her own litter, but the degree of provocation varied greatly among individuals. Females that gave birth to young in live-traps occasionally ate one or more of their newborn young, as evidenced by discarded remnants. ”