Eutamias Amoenus Research Articles

Heterogeneity of Muscle Fibers in Some Burrowing Mammals

Proportional differences in type of fibers within homologous muscles of different burrowing mammals may be a paramount factor determining variation in strength, especially in the relatively unspecialized diggers. The proportions of types of fibers in seven pectoral muscles from two individuals of each of three species of Spermophilus , one species of Scapanus , and one species of Eutamias are demonstrated by comparing variations in glycogen content and differences in diameter. Results indicate the number and kinds of motor units present and thus something about potential gradations in tension. In all species of Spermophilus , muscles showed marked heterogeneity with red fibers predominating. Juveniles of S. beecheyi had a greater proportion of red fibers in most muscles compared to adults, which had a greater proportion of white fibers. This is attributed to ontogenetic change from relatively slow contracting muscles at birth to faster muscles in the adult. Muscles of Eutamias amoenus were primarily red-fibered, which is associated with the high metabolic rate for this species. Muscle fibers of Scapanus latimanus contained high amounts of glycogen but resembled the red fibers of ground squirrels in diameter. Differences in strength between the species of Spermophilus are probably not due to heterogeneity because of the similarity in this factor between muscles. Differences in strength of Scapanus latimanus and Eutamias amoenus when compared to the three species of Spermophilus may be due partly to differences in heterogeneity of muscles. When the proportions of fiber type within a muscle approach equality this implies a greater potential number of motor units that can be recruited. I believe that the heterogeneous muscles of ground squirrels allow the development of relatively great forces, whereas moles develop large forces because of more muscle per body weight and greater mechanical advantage.

Competition Between Two Chipmunk Species (Eutamias)

Two chipmunk species were studied in the mountains of western Alberta from 1961 to 1965. One species, Eutamias minimus, is largely confined to alpine habitat but also ranges into subalpine forest, where its distribution narrowly overlaps that of E. amoenus. The fundamental niches of the two species, estimated from their habitat distributions elsewhere, are both reduced in western Alberta. Mark and recapture trapping in an overlap zone showed that neither species selected habitat deficient in cover and both species made the same relative use of the available forest. The boundary between the two species was not clearly predictable by obvious habitat features. Eutamias amoenus luteiventris is larger than E. minimus oreocetes and, on an average, has larger litters, earlier maturity, and higher populations density. The two species take similar foods, depending on availability in their respective habitats, but the food consumption of individual minimus is less than that of amoenus. In the laboratory, amoenus was highly successful in interspecific encounters with minimus, regardless of whether or not minimus was a resident of the observation cage. In addition, amoenus dominated minimus in a mixed—species group and minimus exhibited avoidance behavior under such conditions. The highly developed aggressive behavior of Eutamias amoenus enables it to exclude E. minimus from subalpine habitats, but the latter survives in alpine situations where its small size is an adaptation to a reduced food supply.

Susceptibility of Various Species of Rodents to the Relapsing Fever Spirochete, Borrelia hermsii

In a study to determine susceptibility to Borrelia hermsii of various rodents commonly found in or near places where human cases of relapsing fever occurred, chipmunks (Eutamias amoenus), pine squirrels (Tamiasciurus hudsonicus richardsoni), flying squirrels (Glaucomys sabrinus), Columbian ground squirrels (Spermophilus columbianus columbianus), golden-mantled ground squirrels (S. lateralis tescorum), wood rats (Neotoma cinerea cinerea), white-footed deer mice (Peromyscus maniculatus), and meadow voles (Microtus pennsylvanicus) were exposed to spirochetes either by bites of infected Ornithodoros hermsi or by injection of infectious tick suspensions. Daily microscopic examination of blood samples revealed that pine squirrels, chipmunks, and meadow voles responded with spirochetemias of various degrees and length. Pine squirrels were most susceptible and experienced long-lasting and severe spirochetemias accompanied by typical signs of illness. Flying squirrels, Columbian ground squirrels, golden-mantled ground squirrels, wood rats, and white-footed deer mice did not develop demonstrable spirochetal infection.

Home Ranges and Territorial Behavior of the Yellow-Pine Chipmunk, Eutamias Amoenus

About 600 chipmunks, Eutamias amoenus, were live-trapped and observed on a study area of 42 acres in yellow pine forest in central Washington. Observation of dyed chipmunks showed that home ranges revealed by live-trapping are reasonably accurate. Evidence that male yellow-pine chipmunks are more active and have considerably larger home ranges than do females is consistent with studies of other mammals. Annual home ranges of adult males averaged 947 by 534 feet and covered 4.07 acres; those of adult females averaged 686 by 368 feet and had a mean area of 2.32 acres. Some ranges were elongate despite a relatively uniform habitat. Adult breeding females had an average of 6.4 neighboring females overlapping their home ranges, the mean area of overlap being 21.7 per cent and number of captures 25.8 per cent. Most chipmunks that were recaptured in the second and fifth years occupied their original home ranges. in 43 homing tests 88 per cent (15 of 17) of the chipmunks returned from points 430 to 1500 feet from home, 57 per cent (12 of 21) from half a mile, and 25 per cent (one of 4) released 1 mile distant. Seventy-seven per cent of the males but only 25 per cent of the females returned half a mile. a shift of home range was accomplished by 7.8 per cent of the females and 11.9 per cent of the males recaptured the second year. Twenty-eight per cent (13 of 46) of the young animals caught in June and July were recaptured in the autumn. Evidence from spacing of chipmunks and from observations of aggressive behavior near the den indicated that they are territorial.

Populations of the Yellow-Pine Chipmunk, Eutamias amoenus

A population of about 600 yellow-pine chipmunks in the Cascade Mountains in central Washington was investigated for approxi- mately 12 months in three different years. The animals were live-trapped on a 42.4-acre study area in yellow-pine forest. There was only one litter in May or June per year. From a base level of 1.54 per acre in May the population rose with emergence of young in June to a peak of 3.13 per acre in July and August based on 3- to 6-day censuses, then gradually declined to 1.64 per acre by September and October. The mean for 1947 was 2.26 per acre. Censuses employing 8 to 12 days of trapping resulted in a mean of 3.20 individuals per acre. By mid-November virtually all chipmunks were in winter burrows. New unmarked animals (most of them young that began appearing in early June) reached a high in July of about 35% of the population. By October 50% of the population were young of the year. An unusual and unexplained change in sex ratio occurred in 1947. The percentage of males which had ranged from 53.5% to 58% through 1946 and to the end of May 1947, steadily dropped through the summer of 1947 to a low of 36% by September. By far the safest time for Eutamias amoenus was the five-month hibernation period, November to April. Survival was nearly 100%. Highest mortality was among young chipmunks in their first weeks above- ground. One-year survival of July, August and September groups aver- aged 29%. Ten per cent of the chipmunks caught in mid-August 1947 were retaken in 1950. Although overlapping in their habitats and foods, the three diurnal sciurids (pine squirrels, Tamiasciurus douglasii; golden-mantled ground squirrels, Spermophilus lateralis; and chipmunks, Eutamias amoenus) all flourished together in considerable numbers. Population density of the chipmunks appeared to be controlled mainly by territorial behavior that spaced individuals a minimum of about 50 feet apart, and by predation from eight diurnal carnivores.

Contributions to the ecology of Colorado tick fever virus.

Studies were conducted in 3 different habitats in Mill Canyon, Ravalli County, in southwestern Montana on certain biological phenomena that affect the dispersal and maintenance of Colorado tick fever in its natural biocenose. During the study 399 small mammals were captured, in descending order of frequency: Peromyscus maniculatus, Citellus lateralis, Neotoma cinerea, Eutamias amoenus, Clethrionomys gapperi, Microtus longicaudus and Glaucomys sabrinus. Capture-recapture data did not prove amenable to statistical treatment, so comparisons of population levels were made by animals caught per-trap-night. Of the rodents collected, P. maniculatus proved most amenable to manipulation, and populations of this species were stable and uniformly distributed throughout the study area. Adult D. andersoni occurred primarily in alpine meadows; larvae mainly in rock ledges in the same area; nymphs for the most part did not respond to the CO2 technique. Adults and nymphs were active during May to July, while larvae were collected July and August. Infestation of rodents ranged from 16% in C. gapperi to 100% in C. lateralis. C. lateralis and N. cinerea were most often infested: average 7–12 ticks per capture. Ixodes ochotonae was also recorded in the study area. Virus was isolated 32 times from pools of D. andersoni nymphs and larvae off rodents but never from wild-caught unfed larvae. Positive pools ranged from 15% in 1964 to 35% in 1966. The greatest number of positive pools (20–53%) was taken from C. lateralis and N. cinerea. In 1964, 11 of 315 P. maniculatus blood samples, 3.5%, were positive for CTF virus; in 1966, 4 of 68 rodent blood samples, 5.9%, were positive. These latter isolations consisted of 2 samples from P. maniculatus and 2 from C. lateralis. The significance of the data gained in this study in the maintenance of CTF virus within the biocenose is discussed.

A comparison of reproduction in two chipmunk species (Eutamias)

Eutamias amoenus and E. minimus are potential competitors in western Alberta. The former species has larger litters and reproduces at an earlier age, on an average, than the latter. Other aspects of reproduction (breeding season, prenatal mortality) do not appear to differ greatly, though supporting data are somewhat inadequate. The higher reproductive potential should confer an advantage on amoenus in competition with minimus. The observed difference in litter size of these two congeners seems to be best explained by a difference in available food in the two habitats. This hypothesis should be tested by a comparative study of the energetics of the two species populations.

Seasonal Changes in Body and Adrenal Weights of Chipmunks (Eutamias)

Body weights of Eutamias amoenus luteiventris (Allen) and Eutamias minimus oreocetes Merriam collected in western Alberta were low in April on emergence from hibernation and increased through May and June to a constant summer level. Adrenal weights were also low at the time of spring emergence but increased steadily, reaching a peak in July and August. In the case of breeding males, this seasonal increase in adrenal weight was delayed until the breeding season had ended but increase was rapid thereafter and relative adrenal weights of breeding males were comparable with those of the rest of the population by July. Limited data suggest a decrease in adrenal size before hiber¬nation. Seasonal changes in adrenal weight may be related to seasonal changes in social interaction but could just as readily be related to other seasonal variables such as reproduction, hibernation, food-gathering activity, length of foraging move¬ments, and density of vegetative cover.

Molts of the Yellow-Pine Chipmunk, Eutamias amoenus

The molting cycle of the yellow-pine chipmunk, Eutamias amoenus affinis, in the Cascade Mountains of Washington was studied. Details of pattern and sequence were obtained from animals dyed black before each molt and from young born and raised in captivity. Field data came. from the live-trapping of about 600 chipmunks. Except for the tail and rump, which shed only once, there were two complete molts each year, one beginning in May (adults) or June (young) and the other in September. On dyed chipmunks, 44 more or less distinct molting areas were observed. Some corresponded with color patterns, but the conspicuous dorsal stripes did not have separate molts. In spring, young animals began to molt on the head but very soon new hair also began to appear on the body and limbs. Overall progress on the head was posterior. On the body the sequence moved up from the sides to form a saddle across the back, then forward over the shoulders and backward to the rump; ventrally the movement was from mouth to belly. The tail molted next, and the last of the body to be renewed was the rump. The limbs shed first on the toes, and front legs preceded the hind. The crown and the heels finished molting at about the same time as Lhe rump. Adults in their spring molt differed from young in three ways: (1 ) in adults, a patchy or spotted pattern preceded the overall molt on the back, (2) the main molt of the body moved from shoulders to rump following an early spotty period, and (3) adults took twice as long as young (about 120 days) to complete this molt. The fall molt moved rapidly forward from rump and belly in both young and adult. The crown and nose were last. Adult males in the population as a whole had peaks of molting in spring and summer in the order: (1) head, (2) shoulders, (3) back, (4) chest and then belly, (5) tail, and (6) rump. In adult breeding females the shedding of the body was delayed. In the whole population the spring molt took about 144 days, but if tail and rump are omitted the time was only 1 10 days. The fall molt (not involving tail and rump) took 93 days. The. entire cycle spanned approximately 168 days from 1 May until 15 October in 1947. Young chipmunks were later than adults in both spring and fall cycles. A complete summer pelage lasted only a week or two, but the winter coat was worn 8 to 11 months. The molting cycle was about 3 to 4 weeks later in 1946 than in 1947, possibly because of a difference in weather in the two years. The underfur on the back is 1.4 times as long (7.6 mm) and 2.7 times as dense (174 hairs per mm2) in winter than in summer. Appropriate temperature regulation and protective coloration in different seasons probably are the most compelling reasons for the two molts and two pelages each year.

Colorado tick fever. I. Further ecological studies in Western Montana.

sharply localized and could be correlated with the presence or absence of the golden-mantled ground squirrel (Citellus lateralis tescorum). This rodent was found to be the principal carrier of CTF virus and the preferred host of immature stages of the tick vector, Dermacentor andersoni. In areas populated by this squirrel, incidence of infection in adult ticks collected from vegetation was as high as 16 per cent and virus was isolated from golden-mantled ground squirrels as well as from other rodents such as Columbian ground squirrels {Citellus columbianus columbianus), chipmunks (Eutamias amoenus), one pine squirrel (Tamiasciurus hudsonicus richardsoni) and one deer mouse (Peromyscus maniculatus). In 1959, similar studies were conducted in 3 of the areas to confirm previous findings and to record any changes that might have occurred in host-vector relationships. The following ecologic data were collected in these areas during 1958:

Observations on Chipmunks and Mantled Squirrels in Northeastern California

During an investigation into the influence of rodents on reforestation, the Division of Zoology of the University of California iat Davis trapped, autopsied, and studied 1,340 chipmunks and mantled squirrels. This work was done in cooperation with the California Forest and Range Experiment Station of the United States Forest Service. Its aim was a better understanding of the biology of diurnal rodents which, primarily because of their seed-eating habits, are accused of hindering reforestation. This paper gives selected facts and conclusions which resulted from the survey. Food data were analyzed separately. Trapping started in mid-September of 1950 and ended one year later. Chiefly it was restricted to the Quincy area, which includes mountainous, coniferous terrain within thirty miles of the town of Quincy in Plumas County of northeastern Califonia. Four species of chipmunks (Eutamias amoenus, speciosus, townsendii, and quadrimaculatus) and the mantLed squirrel (Citellus lateralis) constitute a population unit of the important diurnal rodents of the area at altitudes from 4,500 to 5,500 feet, but numerical ratios between them differ with habitat.