The population dynamics of Microtus townsendii in a linear habitat were monitored weekly for one year (June, 1971-August, 1972). Demographic characteristics such as location on study area, sex, weight (age), reproductive condition, and survival were recorded weekly. An Intensive study of early Juvenile survival was also undertaken. The population was observed to decline in the spring of 1972 from peak densities the previous summer and early spring. The decline did not appear to result from decreased reproductive effort or dispersal, but could be explained solely on the basis of mortality. Several observations were made which did not follow the usual demographic trends in microtine population biology. Extremely high densities with small home ranges for individuals were found on the linear study area as compared with areas of continuous habitat. This population became sexually mature at much lower body weights than other populations of Microtus townsendii in the area and average body weights were lower, although growth rates were comparable. / Science, Faculty of / Zoology, Department of / Graduate

A number of field studies on small mammals have suggested that aggressive behavior may limit breeding density. To investigate how the presence of one individual affects another's chances for survival, reproduction, and growth, I carried out a series of experimental studies on Microtus townsendii near Vancouver, Canada. In the first experiments, population density was reduced by removing voles before or during the spring decline. Drastic artifical reduction during a spring decline improved female survival but not male survival; similar reduction in the fall prior to a decline improved both male and female survival. Survival was not density-dependent in males, but was in females during one decline. To explain these results, a behavioral model is proposed in which females compete for nest sites and males compete for females. In a second experiment, a population predicted to experience a decline was enclosed. I wanted to see if preventing emigration would stop the decline. Unfortunately the control area remained at peak densities and neither area suffered a spring decline. The enclosed population had higher rates of increase, reached higher densities, and had higher survival rates than those on the control area. This resulted in severe overgrazing and a sharp population decline within the enclosure. These results indicate that movements play a necessary role in population regulation when voles are at peak, densities. In a third experiment, the role of predation in causing population changes was measured. Predation was not necessary to initiate a decline or to maintain it. Of the tagged voles known to have been eaten, there was no consistent selection by predators for either of the saxes, for any weight class, or for voles with any other characteristic that could be measured by live-trapping. Of the total number of voles known to have been eaten, avian predators consistently chose animals that were smaller than those in the tagged population. This indicates that either the live-traps selectively caught large animals, or avian predators selectively caught small animals, or that both biases were present. In the fourth experiment, the role of resident adults in determining juvenile survival was tested by removal of adults and by adding juveniles to experimental populations. Survival of young was improved in the absence of all adults, but not in either intact populations, in reduced populations, or in female populations. Survival of young was better in periods of reduced adult breeding. Height at sexual maturity tended to be higher in the presence of adults of the same sex. Growth in young males tended to be reduced in the presence of adult males. These results indicate that females reduce survival of young, and suggest that emphasis be placed on the study of female behavior as a factor affecting microtine numbers. In the final experiment, the survival and dispersal rates of very young voles were examined to determine where the enormous loss between birth and recruitment occurred. A high density vole population was trapped concurrently with live-traps and pitfall traps. Capture of a large number of young in pitfalls indicated that mortality was higher among post-weanlings than among any other age group. The pitfall traps enumerated up to twice as many animals as the live-traps, and over half of the 1100 animals caught first in pitfalls were never caught in live-traps. Trapping solely with live-traps may severely underestimate numbers (at least when densities are high) and give inaccurate population statistics. Populations of J. townsendii fluctuate in size and Chitty's behavior hypothesis predicts that spacing behavior underlies these density changes. My experimental results are consistent with this general view and add specific details to the mechanism by which density is regulated. My experiments pinpoint post weaning survival as a critical phase determining population changes in this vole and focus attention on two critical areas: adult female - postweanling interactions and adult female-adult female interactions. / Science, Faculty of / Zoology, Department of / Graduate

Water consumption, and weight loss in response to water deprivation and saline water consumption, were studied in the Eutamias townsendii townsendii from Portland, Multnomah County, Oregon. These chipmunks occupy moist Pacific Northwest forests. The results of these studies suggest that Townsend's chipmunks are dependent on sources of drinking water, at least for normal above ground activity, that their tolerance for water deprivation is comparatively low, and that they are unable to obtain a net gain of water by drinking 0.2 M sodium chloride solutions. Chipmunks cannot drink 0.4 M NaCl solution and survive for more than a few days. Metabolic water and preformed water in air dry food are not adequate to meet these animals' water needs.

A number of field studies suggest that some vertebrate populations are limited by spacing behaviour, , Small mammals of the genus Peromyscus and Microtus exhibit spacing behaviour by possessing home ranges, but they have contrasting patterns of population fluctuation, Deermice (Peromyscus sp.) fluctuate annually but maintain fairly constant numbers from year to year, whereas voles (Microtus sp.) 'cycle', reaching peak densities every 2 to 5 years. One use of the home range is for food-gathering, Therefore, these experiments were designed to investigate the influence of food availability on the home range and population dynamics of local deermice and voles (P. maniculatus austerus and M. townsendii). The addition of food in late winter resulted in a doubling of the number of deermice. Immigration was 2.5 times that of an unfed control. This could be explained since resident deermice reduced the size of their home ranges. Deermice populations with extra food increased their reproductive output compared with controls: larger numbers of mice bred, and for longer periods, more young were recruited, they grew faster and reached sexual maturity earlier. It is suggested that the onset and cessation of breeding in deermice are proximate responses to food availability, Deermouse dynamics may be closely tied to the temporal and spatial availability of food through the spatial organisation of individuals. It is also suggested that females, because of their energy demands for lactation, and their influence on the survival of young, may be more sensitive to these food conditions and hence exert a strong influence on deermouse population dynamics. Vole populations with, low- and intermediate-levels of food peaked at twice the control density, and a population with a high-level of food reached seven times control density. Voles immigrated to established populations, and colonized vacant areas in proportion to the food available. Like deermice, residents reduced the size of their ranges. Breeding was enhanced in all fed vole populations. Omnivorous deermice had larger ranges than did the herbivorous voles, but both species responded to extra food by reducing their range size, so the smallest deermouse ranges were the size of large vole ranges. The results indicate that home range size in both species is responsive to food availability, and that the concentration of food in the 'typical' habitats of these small mammals is different. If, as suggested, the heterogeneity of deermouse-food in the forest results in an annual cycle in numbers, then the reduced heterogeneity of vole-food in grasslands may influence vole dynamics. / Science, Faculty of / Zoology, Department of / Graduate

This study describes and analyzes the vocalizations of the Townsend chipmunk (Eutamias townsendii) in Oregon. Tape recordings of calls were collected primarily from Forest Park in Portland (Oregon) during 1970 and 1971, and sonograms of these recordings were produced. Findings were compared with those of Brand (1970) who investigated E. townsendii vocalizations in California. The prominent calls in the vocal repertoire of townsendii are the quist, the quirt, and the chipper. These calls all appear to be warning calls. The quist note is a a chevron-shaped (A) figure representing a sound which begins at a low frequency (1-2 KC), sharply rises to a peak at about 11 KC, and then drops sharply to the lower frequencies again. Quists are arranged into bursts, and bursts into sequences. The number of quists per burst and the frequency of the top of the note decreased significantly over time. The interval between burst increased significantly, while the interval between quists seems to increase over time. The variation in the quist rate and related character6istics between Oregon and California townsendii populations is probably a result of subspecific differences. There seems to be a trend in the sciurids from the specific vocal system (one definite meaning per call) of the forest dwellers towards the unspecific vocal systems of animal groups which live in the more open habitats. E. townsendii displays a specific vocal system in which each call seems to have a specific function.

No description available.

Field and laboratory studies were conducted to develop a model of energy expenditure in a population of white-tailed jackrabbits (Lepus townsendii). Field work in southwestern Wyoming during 1985-87 showed that the breeding season commenced at snowmelt and ceased during late- July drought. Adult females reproduced relatively synchronously and produced a mean of three litters annually. Greatest fetal production occurred in the second litter period. Collections indicated a 1:1 sex ratio, few jackrabbits >2 years-old, and a density of 7 animals / km2 in the population. Postnatal growth was sigmoidal, culminating in heavier adult females than males. Using radio -telemetry, a circadian rhythm was detected in jackrabbit activity, with movement beginning after sunset and ending by sunrise. Observations showed that season, snow cover, weather, lunar phase, and predators influenced activity. Energetics studies established the pattern of seasonal acclimatization in the jackrabbit. Basal metabolic rate (BMR), pelage thickness, and body temperature increased but overall thermal conductance (C) and the lower critical temperature (LCT) declined from summer to winter. High winds and low air temperatures elevated metabolism interactively and their effects were most pronounced during summer. Metabolic rate dee lined with incident radiation at Ta< LCT during winter but not during summer. In newborn jackrabbits, body temperature dropped despite increased metabolism at Ta< 25°C. Cold tolerance and homeothermy developed with age. Based on these and published data, a FORTRAN model was written that simulated the energy expenditure of a population of jackrabbits. Metabolizable energy requirements for maintenance , thermoregulation, reproduction, growth, and activity were estimated. The model indicated that most energy (kJ·kg - l.day- 1) was required by adult females during lactation, adult males at the onset of breeding, and newborn juveniles. Energy expenditures for adult females, adult males, and juveniles were 191, 130, and 224 MJ·individual-1·km-2·yr-1, respectively. Total energy expenditure increased with wind and lower air temperature and decreased if juvenile huddling was simulated. The model indicated that the jackrabbit population is not limited by food. Estimated percent consumption of forage energy was 4%, assuming 50% of phytomass was edible, the population density = 100 jackrabbits/km2, metabolizable energy efficiency= 0.4, and the air was calm.