Eutamias Amoenus Research Articles

Flavor avoidance learning and its implications in reducing strychnine baiting hazards to nontarget animals

EL HANI, A., J. R. MASON, D. L. NOLTE AND R. T. SCHMIDT. Flavor Avoidance learning and its implications in reducing strychnine baiting hazards to non-target animals. PHYSIOL BEHAV 64 (5) 585–589, 1998.—In reforested areas, underground strychnine baiting to control pocket gophers ( Thomomys mazama) poses a hazard to golden mantled ground squirrels ( Spermophilus lateralis) and yellow pine chipmunks ( Eutamias amoenus). We designed this study to assess whether: 1) chemical insensitivity to bitter tastes might explain the ingestion of strychnine; 2) pocket gophers would avoid four bitter-tasting compounds: quebracho (QUEB), sucrose octaacetate (SOA), quinine hydrochloride (QHCl), and denatonium benzoate (DB); and 3) nontarget species could be trained to avoid strychnine paired with the most aversive compound. Our results showed that while all species readily consumed strychnine, the nontarget species could be conditioned to avoid it. Moreover, while high (0.1%) concentrations of DB, quinine hydrochloride, and quebracho reduced consumption by pocket gophers, 0.05% DB was inoffensive. Nontarget animals readily avoided 0.05% DB, and avoidance was stronger after conditioning. Together, our results suggest that all of the rodents tested are insensitive to strychnine, high concentrations of some bitter tastes may be effective pocket gopher repellents, and lower concentrations of DB may selectively repel nontarget animals from strychnine baits.

Population dynamics of small mammals in relation to vegetation management in orchard agroecosystems: compensatory responses in abundance and biomass

This study was designed to test the hypothesis that habitat alteration with intensive herbicide (glyphosate) treatment would adversely affect the small mammal community in apple orchards. Multiple applications of herbicide were applied to the total orchard floor in two experimental orchards, and this same herbicide regime was applied in a 2-m-wide strip within tree rows only in a third orchard. Intensive sampling of montane vole ( Microtus montanus), deer mouse ( Peromyscus maniculatus), and northwestern chipmunk ( Eutamias amoenus) populations was conducted in replicate control and treatment blocks of apple orchards at Summerland, British Columbia, Canada from 1983 to 1986. Average abundance of voles declined by 53% to 73% on treatment compared to control blocks after the first herbicide application. Vole populations were consistently reduced in response to the herbicide treatment, with average abundance ranging from 2.8 to 28.0 times higher on control than treatment blocks. Voles declined to, or near, extirpation in all orchards during the winter of 1985–1986. Either deer mouse and northwestern chipmunk populations were significantly higher on treatment than control blocks or there was no difference in abundance after the start of the herbicide applications. The average abundance of deer mice ranged from 1.3 to 11.1 times higher, and that of chipmunks ranged from 1.8 to 13.3 times higher, on treatment than control blocks. The high numbers of deer mice and chipmunks on treatment blocks were composed mainly of resident animals. There were no significant differences in biomass of small mammals between control and treatment populations in summer and winter periods in two out of three orchards. There appears to be a ‘compensatory response’ in this small mammal community whereby deer mice and northwestern chipmunks have essentially ‘replaced’ the montane vole on treatment blocks in an orchard agroecosystem. The quality of the altered habitats seemed sufficiently high to support these populations at comparable or higher levels than on controls. The species diversity of plants and animals in orchard agroecosystems should be investigated to determine their role as part of a mosaic of natural and agrarian habitats.

The degree of dietary fatty acid unsaturation affects torpor patterns and lipid composition of a hibernator.

Diets rich in unsaturated and polyunsaturated fatty acids have a positive effect on mammalian torpor, whereas diets rich in saturated fatty acids have a negative effect. To determine whether the number of double bonds in dietary fatty acids are responsible for these alterations in torpor patterns, we investigated the effect of adding to the normal diet 5% pure fatty acids of identical chain length (C18) but a different number of double bonds (0, 1, or 2) on the pattern of hibernation of the yellow-pine chipmunk, Eutamias amoenus. The response of torpor bouts to a lowering of air temperature and the mean duration of torpor bouts at an air temperature of 0.5 degree C (stearic acid C18:0, 4.5 +/- 0.8 days, oleic acid C18:1, 8.6 +/- 0.5 days; linoleic acid C18:2, 8.5 +/- 0.7 days) differed among animals that were maintained on the three experimental diets. The mean minimum body temperatures (C18:0, +2.3 +/- 0.3 degrees C; C18:1, +0.3 +/- 0.2 degree C; C18:2, -0.2 +/- 0.2 degrees C), which torpid individuals defended by an increase in metabolic rate, and the metabolic rate of torpid animals also differed among diet groups. Moreover, diet-induced differences were observed in the composition of total lipid fatty acids from depot fat and the phospholipid fatty acids of cardiac mitochondria. For depot fat 7 of 13 and for heart mitochondria 7 of 14 of the identified fatty acids differed significantly among the three diet groups. Significant differences among diet groups were also observed for the sum of saturated, unsaturated and polyunsaturated fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Diversionary Food on Red Squirrel Populations and Damage to Crop Trees in Young Lodgepole Pine Forest.

This study was designed to test the hypothesis that large-scale provision of diversionary food (sunflower seeds) would reduce red squirrel (Tamiasciurus hudsonicus) feeding damage to lodgepole pine (Pinus contorta) crop trees. Study areas with managed lodgepole pine stands were located near Vernon and Quesnel in south-central British Columbia, Canada. Large-scale applications of sunflower seeds were conducted on a manual basis in 1989, and by manual and aerial means in 1990, and an operational level by aerial means in 1991. Feeding damage to crop trees was assessed in control and treatment blocks. Populations of the red squirrel, northwestern chipmunk (Eutamias amoenus), and Columbian ground squirrel (Spermophilus columbianus) were sampled intensively by live-trapping on control and treatment blocks in 1990. Manual application of seed (clumped distribution) significantly reduced damage in the treatment block (11.3% of trees damaged) compared with the control (57.5% of trees damaged). Aerial application of seed (uniform distribution) also significantly reduced damage in replicated treatment vs. control blocks. Provision of diversionary food resulted in a temporary increase in the overall number of red squirrels caught on the treatment areas followed by a return to control levels within 6 wk. This increase was primarily the result of an increased number of transients in the trapped sample. The population density of resident (transients excluded) red squirrels did not increase when diversionary food was added. Similarly, we could not detect differences in reproduction, body masses, or survival of squirrels between control and food-supplemented areas. Northwestern chipmunks and Columbian ground squirrels also showed a temporary increase in density when food was added. Application of sunflower seed on an operational basis significantly reduced damage by squirrels in replicated study areas covering three different forest ecological zones. Provision of diversionary food is an effective strategy to protect intensively managed stands of lodgepole pine from red squirrel feeding damage.

Digesta Retention and Digestive Performance in Sciurid and Microtine Rodents: Effects of Hindgut Morphology and Body Size

To examine the effects of hindgut morphology and body size on the digestive performance of rodents, we fed diets of three different fiber contents (7%, 22%, and 28%) to three species of sciurids-yellow-pine chipmunks (Eutamias amoenus) (55-60 g body mass), Columbian ground squirrels (Spermophilus columbianus) (600-700 g), and hoary marmots (Marmota caligata) (2,000-3,000 g)-and to Townsend voles (Microtus townsendii) (55-60 g), a microtine rodent. All species generally maintained body mass on all three diets, except that chipmunks lost mass on the high-fiber diet. We measured intake and digestibility of the three diets and compared rates of passage of fluid digesta (marked with Co-EDTA) and large particles (marked with Cr-mordanted plant cell walls) on the 7% fiber diet. For voles, the mean retention time (MRT ± SE) of fluid (14.8 ± 1.9 h) was greater (P = 0.02, paired t-test) than that of large particles (13.1 ± 2.4 h). This indicates separation of digesta phases in the proximal colon and selective retention of fluid digesta, probably in the cecum, which means that small, highly digestible food particles as well as bacteria are preferentially held in the cecum, which results in a more efective digestion by this system. In contrast, in the three sciurids, MRTs of fluid were the same or less than those of large particles, indicating no selective fluid retention. Among all species, MRTs increased with increasing body size. Dry matter digestibility was greater in the voles than in the chipmunks for all three diets and was greater in marmots than in voles for the low-fiber diet. Our results confirm the general prediction that voles can utilize more fibrous foods than chipmunks because of separation of digesta in a more complex proximal colon and selective retention of fluid in a larger cecum. Within the Sciuridae, increasingly larger body size (and hence a larger absolute gut capacity relative to metabolic rate) offsets the disadvantage of the relatively simple sciurid hindgut.

Influence of polyunsaturated and saturated dietary lipids on adipose tissue, brain and mitochondrial membrane fatty acid composition of a mammalian hibernator

Dietary lipid composition profoundly influences the hibernation pattern of the chipmunk Eutamias amoenus. The object of the present study was to investigate whether these physiological changes following feeding of saturated and unsaturated lipids were associated by compositional changes of fatty acids of tissues and membranes. Animals were fed with rodent chow (control diet), rodent chow with 10% sunflower seed oil (unsaturated diet) and rodent chow with 10% sheep fat (saturated diet). Diet-induced changes in the fatty acid composition of depot fat and brain total lipids and of mitochondrial phospholipids were determined. The fatty acid unsaturation index was lower in animals on saturated diet than in animals on unsaturated diet (depot fat 86.1 vs. 145.9; heart mitochondria 207.6 vs. 247.1; liver mitochondria 148.4 vs. 173.5). Pronounced differences between dietary groups were also observed in n − 3 or n − 6 fatty acids or their ratios of depot fat, brain and liver mitochondria. Generally, the diet-induced differences in tissue and membrane fatty acid composition in E. amoenus were more pronounced than those observed previously in non-hibernating species. Selective feeding and incorporation of high amounts of unsaturated fatty acids into tissues and cell membranes may be an important preparation for hibernation in E. amoenus which lowers its body temperature during torpor to about 0δC.

Torpor Bout Duration during the Hibernation Season of Two Sciurid Rodents: Interrelations with Temperature and Metabolism

Torpor bouts of mammalian hibernators are generally shorter at the beginning and end and are consistently longer during the main part of the hibernation season. Because it is not known why the duration of torpor bouts changes at the beginning and end of the hibernation season, we studied this phenomenon in two sciurid rodents: Spermophilus saturatus (200–300g) and Eutamias amoenus (45-60g). We examined the seasonal change in torpor bout duration during hibernation at a constant air temperature (Ta) of 2° C in relation to (1) the minimum body temperature (minimum Tb) to which the animals could be experimentally cooled before they maintained a constant Tb or began to arouse, (2) Ta at the time of minimum Tb (minimum Ta), and (3) oxygen consumption (V̇o2) of torpid individuals at Ta 2° C. Average duration of torpor bouts during the main part of the hibernation season was about 11 d in S. saturatus and 8–9 d in E. amoenus; in response to experimental cooling, minimum Tb of both species declined as low as −0.2° C. In early and late hibernation, when torpor bouts were short, minimum Tb, minimum Ta, and V̇o2 during torpor were higher than in the main part of the hibernation season. Regression analyses suggest that minimum Tb and minimum Ta are more strongly correlated with torpor bout duration than V̇o2 in both species.

Influence of Orchard Floor Management on Vole and Pocket Gopher Populations and Damage in Apple Orchards

Abstract Removal of all vegetation with herbicides over the total orchard floor or only in tree rows significantly reduced montane vole (Microtus montanus Peale), meadow vole (M. pennsylvanicus Ord), and northern pocket gopher (Thomomys talpoides Richardson) populations and damage. Herbicide treatments in four test orchards were carried out during May, July, and Sept. 1983 to 1985. Average overwinter abundance of voles was reduced 53% to 99% on treatment areas. Several vole populations went to extinction in the third year of herbicide treatment. Incidence of tree damage was 40.6% and 9.6% with feeding intensities of 17.2 cm2 and 0.4 cm2 of bark and tissues removed per tree on control and treatment blocks, respectively, during a peak year in abundance of voles. Pocket gopher populations and damage were significantly lower in treatment than control blocks. Deer mouse (Peromyscus maniculatus Wagner) and yellow pine chipmunk (Eutamias amoenus J.A. Allen) populations generally increased on treated areas. Use of herbicides to control orchard floor vegetation is an effective means of rodent damage control.

Polyunsaturated lipid diet lengthens torpor and reduces body temperature in a hibernator.

Membrane lipids of vertebrate animals that tolerate cold are high in polyunsaturated fatty acids. Because the lipid composition of cellular membranes in mammals can be experimentally altered by diet, we investigated whether a diet rich in polyunsaturated fatty acids would lengthen bouts of torpor and reduce the minimum body temperature in hibernating chipmunks (Eutamias amoenus) compared with a diet rich in saturated fatty acids. Animals on the highly unsaturated diet showed significantly longer bouts of torpor, lower minimum body temperatures, and lower metabolic rates than those on a saturated diet. Animals on a control diet were intermediate. These dietary adjustments apparently influence the control of body temperature by the central nervous system, which results in a modification of the pattern of torpor. The observations also suggest a role of nutritional ecology in hibernation.

Notes on Mycophagy of the Yellow-Pine Chipmunk (Eutamias amoenus) in Northeastern Oregon

Notes on Mycophagy of the Yellow-Pine Chipmunk (Eutamias amoenus) in Northeastern Oregon

The Influence of Interspecific Competition on Home Range Size in Chipmunks (Eutamias)

The influence of interspecific competition on home range size of two sympatric chipmunks, Eutamias amoenus and E. townsendii , was studied experimentally on two 6.24 ha grids in the Cascade Mountains of eastern Washington from 1980 to 1982. The species overlap in habitat use, diet, and time of daily activity (Pianka's Index of Overlap = 0.34, 0.62, and 0.98, respectively). Regression analysis of eight measures of vegetation structure with number of chipmunk captures suggests that in the study area these species do not use separate microhabitats ( P > 0.05). Behavioral interactions between the species are highly agonistic and E. townsendii is dominant over E. amoenus ( P < 0.001). In June 1981, all resident E. townsendii were removed from one of the grids. Relative to the control grid, the home range size of resident E. amoenus on the experimental grid increased after the removal of E. townsendii ( P < 0.05). In addition, the absence of E. townsendii led to an increase in juvenile recruitment of E. amoenus ( P < 0.05). These results are interpreted with respect to the costs and benefits to an animal of using a given amount of space. When resources are not partitioned and interactions between species are aggressive, interspecific competition results in an increase in the cost of using an area and a decrease in home range size.

Susceptibility of Small Mammals to Nonvirulent Spotted Fever Group Rickettsiae1

Studies were performed to evaluate the significance of the Golden-mantled Ground Squirrel, Spermophilus lateralis tescorum, the Columbian Ground Squirrel, Spermophilus columbianus columbianus, and the Yellow-pine Chipmunk, Eutamias amoenus, as sources of infection for the nonvirulent spotted fever group rickettsiae Rickettsia montana (M/5–6 B strain) and R. rhipicephali (3–7 ♀ 6 strain). Results indicated that none of 16 animals developed a rickettsemia following intraperitoneal (i.p.) inoculation of 200 egg-infectious doses (e.i.d.) of R. montana. Similarly, none of 12 animals developed detectable rickettsemias following i.p. inoculation of R. rhipicephali. Conversely, all 6 animals, 2 per species, responded with rickettsemias following inoculation of virulent R. rickettsii (Sawtooth ♀ 2 strain). Furthermore, none of 991 ticks that fed on animals inoculated with R. montana showed evidence of rickettsial infection, whereas low infection rates of 0.9 and 0.5% were recorded for ticks that fed on a single Golden-mantled Ground Squirrel and chipmunk, respectively, that had been inoculated with R. rhipicephali. None of 781 ticks that fed on the remaining 4 rodents showed evidence of infection. However, infection rates up to 11.0% were noted in nymphal ticks that had fed as larvae on Golden-mantled Ground Squirrels, chipmunks, and Columbian Ground Squirrels infected with R. rickettsii. These observations suggest that Golden-mantled Ground Squirrels, chipmunks, and Columbian Ground Squirrels are of little or no significance in infecting ticks with R. montana or R. rhipicephali.

Habitat Use by Sympatric Species of Eutamias

Differences in habitat use were investigated for four species of chipmunk ( Eutamias amoenus , E. speciosus , E. senex , and E. quadrimaculatus ) that occupy overlapping areas of roughly equal elevation in the northern Sierra Nevada. Livetrapping on six study plots was conducted over a 3-year period. Differences in vegetation structure among plots were quantified, and factors correlated with occurrence of each chipmunk species were identified by discriminant analysis. Three of the congeners appeared to exhibit preferences for different habitats. Only E. senex was found in closed-canopy forest. E. speciosus was associated only with areas of scattered trees. E. amoenus was almost the exclusive resident of brush plots and other disturbed areas but overlapped extensively with E. speciosus in open forest. The data suggest that the existence of different vegetational types accommodates overlapping occurrence of these species within a single altitudinal zone.

Quantitative immunological studies of the albumins of North American squirrels, family Sciuridae

1. 1. Rabbit antisera against purified serum albumin of Spermophilus tridecemlineatus, Spermophilus lateralis, Ammospermophilus nelsoni, Eutamias amoenus, and Sciurus niger were used to probe relationships within the Sciuridae. 2. 2. Quantitative micro-complement fixation tests indicated that ground squirrel ( Spermophilus and Ammospermophilus) and chipmunk ( Eutamias) albumins were more similar to one another than any were to tree squirrel ( Sciurus) albumins. 3. 3. Spermophilus tridecemlineatus appears more distantly related to other Spermophilus than are Ammospermophilus, Marmota, and Eutamias.

Behavioral Factors in the Altitudinal Zonation of Chipmunks (Eutamias)

Behavioral factors important in the determination of the lines of contact between 3 altitudinally zone chipmunks, Eutamias minimus, Eutamias amoenus, and Eutamias speciosus, were investigated at a field site in the Sierra Nevada, California. These species are contiguously allopatric and restricted to particular vegetational communities. Extensive mark—release—recapture studies and a removal experiment suggested that the E. minimus—E. amoenus border results from a physiological limitation of E. amoenus and competitive exclusion of E. minimus from E. amoenus habitat. In areas where E. amoenus were removed, E. minimus captures increased; the converse did not occur. Behavioral observations coupled to vegetation surveys showed that E. amoenus had a much stronger preference for the vicinity of trees than the other species. Eutamias minimus, because it is physiologically more capable of handling dry heat loads than E. amoenus, showed a weaker orientation to trees. Eutamias speciosus shows even less orientation to trees, even though it is the most vulnerable of the 3 to heat stress. Field observations of interactions revealed that all 3 species are highly aggressive intraspecifically, and that a clear—cut interspecific dominance hierarchy exists: E. speciosus dominates both E. amoenus and E. minimus, and E. amoenus in turn dominates E. minimus. The evolution of aggressiveness is explained in terms of the hibernation strategy of the animals and the concomitant need to storage large quantities of food for the winter. Interspecific aggression is not selected against because of large overlaps in food utilization among the species. It is concluded that physiological and behavioral factors interact to produce the contiguously allopatric distribution of these chipmunks: E. speciosus aggressively excludes other species from its forest habitat, to which it is restricted by physiological considerations and habitat selection; E. amoenus tolerates the more severe conditions in arid woodlands, from which it excludes E. minimus; E. minimus has extensive thermoregulatory adaptations enabling it to inhabit the extremely hot, dry sagebrush, which is intolerable for the more aggressively dominant species.

Some aspects of overwintering in the chipmunk, Eutamias amoenus

Seasonal changes in size, food consumption, and activity were measured in Eutamias amoenus housed in cages with nest boxes and exposed to seminatural meteorological conditions at Lethbridge, Alberta, Canada. Decreases in food consumption, activity, and size were recorded in winter months. Results suggest reduced growth and activity in winter are effective mechanisms of energy conservation in this species.

Interspecific Agonism in Two Parapatric Species of Chipmunks (Eutamias)

The chipmunk species Eutamias minimus oreocetes and Eutamias amoenus luteiventris are altitudinally parapatric in the Rocky Mountains of southern Alberta; E. m. oreocetes occupies the alpine, E. a. luteiventris occupies forest. During simultaneous introductions of these subspecies into a large structurally complex arena, E. a. luteiventris was dominant in a majority of matches. During matches in which E. m. oreocetes was introduced 1 day prior to the introduction of E. al luteiventris, both species won the same number of matches. Habitat structure appeared to influence the outcome of interactions. Prior residence of a nonforest habitat may provide E. m. orecetes with sufficient advantage in agonistic interactions to exclude E. a. luteiventris from such habitat. Eutamias minimus borealis and E. amoenus ludibundus are geographically parapatric in the Rocky Mountains of central Alberta, Canada; both species occupy forest habitats. During simultaneous introductions of these subspecies into the arena, E. a. ludibundus was dominant in a majority of matches. A comparison of three studies of interspecific agonism between various subspecies of E. minimus and E. amoenus indicates that E. minimus is generally subordinate to E. amoenus regardless of habitats occupied. The distributions of the four subspecies in Alberta suggest that E. amoenus luteiventris displaced E. minimus borealis from the montane forest of southern Alberta, and E. minimus oreocetes may represent refuge populations of E. minimus borealis that successfully excluded E. amoenus ssp. from the alpine.

Local Adaptations in Chipmunk (Eutamias amoenus) Populations and Evolutionary Potential at Species' Borders

A study of four yellow pine chipmunk (Eutamias amoenus) populations distributed along a steep environmental gradient in central Oregon revealed differences verifying a prediction of high evolutionary potential at distributional borders of species occupying unstable environments. Population density was lowest on the coniferous forest edge of the ponderosa pine transition zone (Spiders population), highest near the center of the transition zone (Main Grid), and intermediate in populations at the desert periphery of the ponderosa zone (Cabin Lake) and isolated in a disjunct ponderosa forest on the Oregon High Desert (Lost Forest). Attrition of adult @M @M was greatest during the oversummer periods, and was more likely due to predation than to dispersal. Attrition of adult @V @V was greatest during the overwinter periods. During this period, winter food caches may be exhausted before new supplies appear; these shortages, combined with increases in @V energy demand associated with gestation and rearing of young, may have contributed to overwinter starvation. Significantly higher adult @V body weight at the edge of the dense coniferous forest suggests an adaptive response to spring food shortages caused by late snowpacks and by cool weather inhibition of foraging. At the desert edge of the ponderosa forest, increased body weight may instead be an adaptive response to spring food shortages resulting from fewer seed—producers and from competition with least chipmunks (Eutamias minimus). Competitive advantage among chipmunks is commonly associated with larger size, and E. amoenus @M @M at Lost Forest, which were nearest to E. minimus in body weight, showed the greatest increase over central population weights. Observations at the Main Grid, Cabin Lake and Lost Forest showed behavioral characteristics of the populations to be generally similar, although significant populational differences in activity budgeting were observed. Higher population density at the Main Grid led to a much higher level of positive social interactions with a much higher percentage of aggressive chasing and fighting than at other sites. At Cabin Lake weather had a strong influence on activity budgeting and habitat orientation. Lost Forest chipmunks exhibited a greater proportion of protective behavior (especially alarm vocalizations), suggesting an adaptation by which the population may reduce danger from predation due to low protective cover without restricting the area over which individuals may safely forage. This same population appeared to have adjusted activity budgets to avoid high desert temperatures by foraging more in early hours and orienting more toward the shade of trees and shrubs in later hours. These trends were less pronounced in the peripheral forest—edge population and were reversed in the central population. When foraging, individuals from all populations oriented most strongly toward shrubs, then open ground, slash piles, and trees; they oriented least strongly toward rocks, stumps, or logs. Chipmunks involved in maintenance or protective activities showed a nearly reversed order of preference for the same habitat features. These and other observations suggest that, contrary to recent literature, presently observed lines of contact between allopatric chipmunk species do not represent dynamic tension zones established and maintained in delicate balance by aggressive interactions. Rather, they represent extremely stable distributional limits established through habitat selection as a mechanism by which smaller species may avoid fruitless as well as energetically costly competitive encounters with larger species.

Contributions to the Ecology of Colorado Tick Fever Virus 2. Population dynamics and host utilization of immature stages of the Rocky Mountain wood tick, Dermacentor andersoni1

Relative abundance of larval Rocky Mountain wood ticks, Dermacentor andersoni Stiles, in mountainous terrain of western Montana was measured by release and recapture of radiolabeled ticks. Laboratory-reared larvae tagged with 14-Carbon or 125-Iodine were released in equal numbers at selected points within 1 of 2 study areas during the natural larval activity periods of 1967–1969. Tagged larvae subsequently recovered on small rodent hosts trapped in these areas and identified provided an estimate of tick population size per acre (ha) (±2 S.E.): 119,163 ± 50,864 (294,333 ± 125,633) and 388,622 ± 212,750 (959,896 ± 525,214) in 1967 and 1969, respectively. Hosts from which most of the ticks were obtained were Neotoma cinerea (40.9% of larvae; 30.6% of nymphs), and Spermophilus lateralis (35.1% of larvae; 60.3% of nymphs). Other hosts were Peromyscus maniculatus (17% of larvae; 4.9% of nymphs), and Eutamias amoenus and E. ruficaudus (7.0% of larvae; 6.6% of nymphs). Larval activity was restricted to a 9- to 11-week period between mid-June and early September, peaking once in late July or early August. Nymphal activity, already evident when trapping began, remained constant until it declined after mid-August. Labeling of larval ticks by exposure to radioactive iodine vapor appears to be at least as efficient as labeling them through inoculation of ovigerous parents with 14-Carbon.

Tree Nests of Chipmunks with Comments on Associated Behavior and Ecology

Four additional species of Eutamias ( amoenus, cinereicollis, palmeri , and ruficaudus ), added to E. minimus, speciosus , and sibericus , bring to seven the number of tree-nesting chipmunks. Tree nests were at heights of 2.6 to 23 meters. Those made of grass by E. amoenus and ruficaudus were about 30 centimeters in diameter and were used for more than one year. Most tree nests were in conifers (three in woodpecker holes), one was in a clump of young willows, and one was in a cottonwood. It is during the period of weaning and exploration just before the young disperse that tree nests are used by a mother and her family. Chipmunks appear to be the only sciurids and possibly the only rodents in which the mother and her family use both underground and arboreal nests in a given year. Feeding in the pygmy forest of bushes, chipmunks occupy a special niche between those of ground squirrels and tree squirrels.