• Nutritional and ecological determinants of growth and reproduction in Caribou

      Gerhart, Karen Lynn (1995)
      I investigated the mechanisms by which differences in body weight and body composition (fat, protein) of female caribou (Rangifer tarandus granti) from the Central Arctic and Porcupine herds might determine changes in pregnancy rate and calf growth. Allometric relations between chemical components and body weight variables were highly significant, despite tremendous seasonal changes in composition. Between October 1989 and May 1990, body fat and body protein of adult females of the Central Arctic Herd declined by maxima of 45 and 29%, respectively; an additional 32% of fat was lost by July. Extensive mobilization of fat and protein indicates winter undernutrition. Marked hypertrophy of liver and kidneys in summer suggests the presence of mobilizable protein reserves. Birth weights of calves were similar between sexes, but male calves grew relatively faster during summer and were significantly heavier than females in autumn. Both fat content and growth rate of calves declined between 4 and 6 weeks post-calving, perhaps in response to insect harassment. Weight gains of wild calves were greatly reduced or absent after 100 d of age, while captive calves continued to grow until 175 d, suggesting that first-summer growth of caribou is determined in part by nutrient availability. Birth weight and growth rate of wild calves from birth to 3-4 weeks of age accounted for nearly 79% of the variability in autumn weights, again implying summer nutrient limitation. Female caribou were unable to entirely compensate for the metabolic and ecological costs of lactation: in autumn, lactating females had 42% less fat and 9% less protein than nonlactating females. Unlike females from the Central Arctic Herd, those from the Porcupine Herd did not demonstrate compensatory weight gains over summer; instead, autumn weight was highly correlated to June weight. Probability of pregnancy was positively correlated with body weight and fat content in early winter. Females that extended lactation into November were less fertile than predicted by body size or condition. I believe that these females were exhibiting lactational infertility.
    • Plant-herbivore interactions on the Yukon-Kuskokwim Delta: The effect of goose herbivory on arrowgrass

      Mulder, Christa Pauliene Hilda (1996)
      I examined effects of herbivory by black brant geese (Branta bernicla nigricans) on the small herbaceous perennial Triglochin palustris (arrowgrass) in a subarctic saltmarsh in SW Alaska. I investigated effects of biomass removal, and indirect effects of geese (changes in resource availability and competition) to compare the role of selective herbivory in this mixed-species environment with that of herbivory in monospecific saltmarsh communities. I manipulated nutrient availability, light availability, and salinity in a transplant experiment, and manipulated size of arrowgrass, and neighbor size and feces deposition in exclosure experiments. Additional experiments examined relationships between size, biomass allocation, survival and reproduction, and explanations for low rates of sexual reproduction in arrowgrass. A cellular automata model was used to investigate potential long-term effects of changes in grazing intensity. Direct effects of geese were smaller than indirect effects: biomass removal had little effect on rates of population growth or plant size, and resulting changes in biomass allocation did not affect survival or reproduction. For unclipped arrowgrass, feces deposition resulted in increased competition for light, which was ameliorated by consumption of neighboring plants, but some species may provide protection from grazing. Expansion into neighboring communities is limited by physical factors on the sea-side end of the distribution, and by competition for light and high selectivity on the inland end. Overall effects of changes in grazing pressure will depend on changes in goose foraging behavior and selectivity. Trade-offs exist between sexual reproduction and all other functions, and sexual reproduction may increase risk of herbivory. Goose effects occur at several spatial and temporal scales: immediately (through biomass removal), within a growing season (through changes in competition and resource availability), over several growing seasons (through feedbacks to foraging behavior), and over long periods (through changes in reproduction). Model results suggest increased grazing intensity may not decrease arrowgrass populations under some conditions, and that spatial distribution of geese affects population dynamics of arrowgrass. There is no evidence that feces deposition results in greater productivity of preferred species. More detailed knowledge of goose foraging behavior at several spatial and temporal scales is needed in order to understand the dynamics of this system.
    • Population Characteristics, Ecology, And Management Of Wolverines In Northwestern Alaska (Gulo-Gulo)

      Magoun, Audrey J. (1985)
      A radiotelemetry study of wolverines was initiated in 1978 as part of a larger research program sponsored by the U.S. Fish and Wildlife Service in northwestern Alaska. The primary goal of this research was to determine aspects of wolverine behavior and ecology that are important to the management of wolverines in northwestern Alaska. Between April 1978 and May 1981, 26 wolverines were captured, 12 males and 14 females; 23 were radiocollared. Nine wolverine kits in five litters were produced by three of the radiocollared females between March 1978 and May 1982. The average rate of reproduction for the study population was 0.6 kits/female/year. Birth of kits occurred in early March. Kits grew rapidly, reaching adult size by November. Resident female wolverines maintained home ranges that were exclusive of other females except their offspring; average summer home range size was 94 km('2). Data were insufficient to determine if adult male home ranges overlapped; overlap did occur between adult and juvenile males. Summer home range size for adult males averaged 626 km('2). Data were insufficient to determine annual home range size. Denning and raising young had a major influence on the movement patterns of adult females. Movements of males were influenced by breeding behavior from late winter through summer. Wolverine social structure appeared to be typical of the intrasexual territoriality of solitary carnivores. Wolverines scentmarked frequently using urine and secretions from the ventral gland and anal sacs. Caribou and ground squirrels were the most important foods. Food was apparently limited during the winter months and influenced wolverine movements and productivity. The presence of caribou and moose may be the most important factor influencing wolverine populations in northwestern Alaska. Wolverines do not appear to be overexploited at this time, but an attempt should be made to obtain more accurate harvest statistics and baseline data to establish wolverine population size and structure in northwestern Alaska.
    • Predator-prey dynamics between mountain lions and mule deer: Effects on distribution, population regulation, habitat selection, and prey selection

      Pierce, Becky Miranda; Bowyer, R. T.; Bleich, V. C. (1999)
      Mountain lions (Puma concolor) and mule deer ( Odocoileus hemionus), which share a winter range in the Eastern Sierra Nevada in Round Valley, California, USA, were fitted with radio-telemetry collars and tracked to determine their movements and cause of mortality. The mountain lion population of Round Valley refers to a group of individuals that lived in close proximity to one another, essentially isolated from similar groups during the winter, and fed on the migratory herd of mule deer that overwinter in Round Valley. Mountain lions migrated seasonally with the deer population, and two distinct patterns for coping with variability in abundance of prey were observed. The unique migratory behavior identified for the mountain lions in this study indicates a more flexible social system for mountain lions than previously described. Tests of whether the presence of another mountain lion affected where individuals to killed deer indicated that social interactions had no effect and that social behavior was not regulating the population of mountain lions via spatial partitioning of prey. Examination of habitat selection by mule deer and mountain lions revealed that mule deer selected habitat at higher elevations (P < 0.001) with more bitterbrush ( Purshia tridentata) and less rabbitbrush (Chrysothamnus nauseosum ) than random locations. Mountain lions killed deer in relatively open areas with more desert peach (Prunus andersonii) than locations in which deer foraged. Those results indicated that deer were not confronted with a tradeoff in terms of habitat selection on the winter range because habitat with the best forage (e.g. bitterbrush), also provided the least predation risk. Comparisons of mule deer killed by mountain lions, coyotes, and automobiles indicated that mountain lions selected young (<1 year old) deer and both predators selected older age classes among adults. Furthermore, there was no selection by either predator for animals in poor condition. Among mountain lions in different social categories, female mountain lions with kittens selected more young deer than did other social categories. This study indicated that ambush predators (mountain lions) may be as selective for prey as coursing predators (coyotes) and that lactation in mountain lions may play a role in determining prey selection. ion.
    • Processes controlling nitrogen release and turnover in Arctic tundra

      Kielland, Knut; Chapin, F. Stuart III (1990)
      This thesis provides data on nitrogen cycling among communities representative of the major vegetation types in arctic Alaska. Through field studies, I examined the pattern of nitrogen dynamics in four tundra ecosystems (dry lichen heath, wet meadow, tussock tundra, and deciduous shrub tundra) of contrasting structure and productivity near Toolik Lake, Alaska. In addition, through field and laboratory experiments, I sought to identify the major controls over nitrogen release and turnover in these nitrogen-limited systems. These ecosystems, representing extremes of productivity in arctic Alaska, show order-of-magnitude differences in biomass and net primary productivity, and likewise, exhibit order-of-magnitude differences in net nitrogen mineralization and nitrogen turnover. Decomposition, soil respiration, net nitrogen mineralization, and the turnover of soil inorganic nitrogen were all highly correlated with net primary production. These results show that nutrient availability, in particular nitrogen availability, is a major control over tundra ecosystem function. Soil pools of organic nitrogen are large, whereas the pools of inorganic nitrogen are small, and the net rate of nitrogen mineralization in situ is low. Thus, nitrogen mineralization represents a major control point in the nitrogen cycle. Net nitrogen mineralization is relatively insensitive to changes in soil temperature, but highly responsive to changes in available soil carbon and nitrogen. Thus, the effect of organic matter quality on microbial activity is a more important control of nitrogen release than is the direct effect of temperature. Free amino acids constitute a larger proportion of extractable soil nitrogen than do ammonium and nitrate. Tundra species have the capacity to absorb some amino acids directly at rates comparable to ammonium absorption. These experimental results contrast with the widely held assumption that mineral nitrogen is the only form of nitrogen available to plants. I conclude that we must examine the behavior of both inorganic and organic soil nitrogen in order to adequately understand nitrogen cycling in tundra soils and the functioning of arctic ecosystems.
    • Proximate and ultimate control of reproductive effort in northern shovelers (Anas clypeata) nesting at Minto Flats, Alaska

      Maccluskie, Margaret Christine (1997)
      The purpose of this study was to examine factors that influence reproductive effort of female Northern Shovelers (Anas clypeata) nesting at Minto Flats, AK during summer 1991-1993. I investigated the importance of endogenous nutrient reserves to females during egg production and examined changes in organ weights and intestine lengths through the reproductive cycle. Changes in organ weights and intestine length were similar to those of shovelers nesting in Manitoba. Females used neither somatic lipid reserves, protein reserves, nor mineral reserves to produce eggs. Individual variation in somatic lipid reserves was explained by body size and nest initiation date, while variation in somatic protein reserves was explained by standardized nest initiation date. Somatic mineral variation was explained by differences among years. Neither somatic protein nor mineral reserves were reduced during incubation, but somatic lipid reserves decreased significantly. I conclude that endogenous nutrient availability does not proximately limit clutch size during laying for this population, possibly due to high productivity of interior Alaska wetlands and long days. Little is known about nest attendance behavior of ducks in the subarctic; therefore, I examined shoveler nest attendance patterns at Minto Flats to determine if observed patterns differed from those documented for shovelers nesting in Manitoba, Canada. Shovelers nesting at Minto were less attentive and took more frequent, longer recesses than shovelers in Manitoba. I examined patterns of nest attendance during incubation in relation to clutch volume and female weight loss to determine if females make tradeoffs between energy invested in the clutch and energy invested in incubation. I found no evidence of energetic tradeoffs by Shovelers nesting at Minto Flats. To determine if the trait of synchronous hatching could limit clutch size for a species of the genus Anas I measured development time and metabolic rates of Mallard (Anas platyrhynchos) eggs incubated in a constant environment. Females varied in length of time their eggs required to reach the star-pipped stage of hatch. Metabolic rate of eggs varied positively with position in the laying sequence and varied among females. These results indicate that metabolic rate may act as a synchronization mechanism for hatch.
    • Seasonal diets of mink and martens: Effects of spatial and temporal changes in resource abundance

      Ben-David, Merav (1996)
      Seasonal changes in food availability and feeding habits of mink (Mustela vison) and martens (Martes americana) on Chichagof Island, Southeast Alaska, were studied through the analysis of natural abundance of stable isotopes. Dependence of the two species on marine-derived nutrients, carried to the terrestrial system via the upstream migration of spawning Pacific salmon (Onchorhynchus sp.), was investigated. Twenty-four mink and 75 martens were live-trapped repeatedly in early summer (prior to salmon runs), early autumn (post salmon runs), late winter, and in spring (during the mating season). A blood sample was obtained from each individual. In addition, 25 mink and 165 marten carcasses were obtained from trappers during late autumn 1991-1994. Concurrently, prey availability was monitored, and tissues from prey were collected. The abundance of stable isotopes in prey tissues and blood samples were compared, indicating that riverine mink depended on salmon (carcasses and fry), with little seasonal or individual variation, whereas coastal mink relied on intertidal organisms in spring and summer, but fed on salmon carcasses when they became available in autumn. In addition, analysis of blood progesterone revealed that timing of reproduction in female mink appear to be shifted, so that lactation coincided with the availability of salmon carcasses. In contrast, martens showed individual variation in their diets, with some individuals feeding exclusively on terrestrial organisms, while the diets of others include salmon carcasses. Incorporation of salmon in the diet depended largely on availability of small rodents and location of the martens home range on the landscape. Although salmon carcasses are not a preferred food item for martens, they act as a suitable alternative to maintain body condition and allow successful reproduction even in years when preferred food is not readily available.
    • Seasonal Fungal Biomass Dynamics In An Interior Alaskan Paper Birch (Betula Papyrifera Marsh) And Quaking Aspen (Populus Tremuloides Michx.) Stand And Effects Of Long-Term Fertilization (Fungi, Mycology, Mushrooms, Ecosystem(S))

      Moore, Terry A. (1985)
      Standing crop fungal biomass was measured at bi-weekly intervals for two successive field seasons in contiguous, 50 year old stands of quaking aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh) and in contiguous stands of aspen and birch undergoing long-term fertilization by yearly application of inorganic nitrogen, phosphorus and potassium fertilizers. Soil temperature and moisture were monitored throughout the study. Principal goals were: (1) to delineate seasonal fluctuations in fungal biomass in the forest floor and mineral soils of aspen and birch vegetation sites considered representative of upland, interior Alaskan hardwood taiga; (2) to determine if biomass fluctuations were correlated with fluctuations in soil microclimate; (3) to determine if differences in fungal biomass were correlated with dominant overstory vegetation; i.e. differences in primary or secondary site substrate (resource) quality; (4) to determine if long-term (nine years) application of inorganic fertilizers altered overall standing crop fungal biomass in the two vegetation types studied; and (5) to determine if soil bulk density or microclimate were influenced by vegetation type or fertilization. Results show that seasonal biomass for both control and fertilized sites was closely correlated with soil moisture and exhibited little or negative correlation with soil temperature. Unamended aspen soils supported significantly greater fungal biomass than birch soils due to increased soil moisture, a more favorable chemical environment and production of organic matter more conducive to growth of soil fungi. Fertilization significantly decreased fungal biomass in aspen soils indicating the long-term treatment with inorganic fertilizers could be detrimental to mineral cycling in this forest type. Fertilization significantly increased fungal biomass in birch soils due to increased soil organic matter content and increased soil moisture. Hyphae of basidiomycetes was significantly decreased by fertilization in both vegetation types suggesting that basidiomycetes involved in saprotrophic decomposition and/or mycorrhizal associations were adversely affected by fertilization. The effects of vegetation type and fertilization on soil temperature, moisture and bulk density are discussed.
    • Seasonal Migration And Distribution Of Female Red King Crabs In A Southeast Alaska Estuary.

      Stone, Robert Paul; Shirley, Thomas C. (1991)
      Seasonal movements and distribution of primiparous and multiparous red king crabs (Paralithodes camtschaticus) were monitored approximately weekly for one year in Auke Bay, Alaska, using ultrasonic biotelemetry. Patterns of seasonal movements were generally similar for all crabs, although movements of multiparous crabs were more conservative and coordinated between individuals. Groups of crabs remained in relatively discrete areas for several weeks before moving, usually as a group, to a different area. The annual range of primiparous crabs (x = 11.9 km$\sp2$) exceeded (P $<$ 0.025) that of multiparous crabs (x = 3.6 km$\sp2$). All crabs displayed distinct seasonal shifts in depth distribution and habitat use. Depth distribution was significantly correlated with photoperiod and the abrupt, synchronous movement of crabs between habitats was coincident with thermohaline mixing. Females displayed a highly aggregated distribution, especially during winter in shallowwater areas. Podding behavior of adult crabs was documented for the first time. Possible causes and functions of this highly specialized behavior are discussed. <p>
    • Sexual segregation in desert-dwelling mountain sheep

      Bleich, Vernon Charles; Bowyer, R. Terry (1993)
      Mountain sheep (Ovis canadensis nelsoni) were studied in the eastern Mojave Desert, San Bernardino Co., California to test 4 hypotheses potentially explaining sexual segregation in ungulates. Mature males and females were segregated from December to July, and aggregated from August to November. Mature males obtained higher quality diets than did females (based on fecal crude protein) and forage was more abundant on ranges used by these males. Indices of predator abundance were substantially lower on ranges used by females and young than on those used by mature males. Females occurred closer to permanent sources of water, and in steeper, more rugged, and more open habitats than did mature males. Female groups with and without lambs did not differ in their distance from water during aggregation or segregation. Female groups with lambs, however, occurred on steeper slopes and in more rugged and open habitats during segregation, when lambs were very young. I refute the hypotheses that: (1) Males enhance their fitness by segregating from females and their own offspring; (2) Females outcompete males for available resources, and allometric differences between the sexes lead to sexual segregation; and (3) The constraints of lactation may be important in explaining sexual segregation in this desert-adapted ungulate. In contrast, my observations strongly support the hypothesis that, because of their smaller body size and potentially greater vulnerability to predation, female ungulates use habitats with fewer predators and more opportunities to evade predation than do males, but males are able to exploit nutritionally superior areas. Sexual segregation likely results from differing reproductive strategies of males and females among sexually dimorphic mammals. Males may enhance their fitness by exploiting habitats with superior forage, and thereby enhance body condition, while simultaneously incurring greater risks than do females. In contrast, females appear to enhance their fitness by minimizing risks to their offspring, albeit at the expense of nutrient intake.
    • Soil consumption of atmospheric methane: Importance of microbial physiology and diversity

      Gulledge, Jay Michael (1996)
      Recently, atmospheric CH$\sb4$ concentration has risen dramatically, apparently due to human activities. Since is CH$\sb4$ is involved in several atmospheric processes that regulate Earth's climate, it is important that we understand the factors that control its atmospheric concentration. One such factor is biological CH$\sb4$ consumption in well-drained soils. Although this sink may comprise nearly one-tenth of the annual destruction of atmospheric CH$\sb4$, We know relatively little about it. I conducted a research project to investigate the influences of CH$\sb4$ supply, soil moisture, dissolved salts, and NH$\sb4\sp+$-fertilizer on the activity of soil CH$\sb4$ oxidizers. When starved of CH$\sb4$, two upland taiga soils gradually lost their capacities to oxidize CH$\sb4$, indicating that the process was not merely fortuitous, and that the organisms involved were truly methanotrophic. The relationship between soil moisture and CH$\sb4$ consumption was parabolic, with maximum oxidation occurring at a moisture level that achieved the maximum possible CH$\sb4$ diffusion rate, while minimizing water stress on the methanotrophs. Optimal soil moisture occurred in a relatively narrow range among an array of physically dissimilar soils, providing that moisture content was expressed as a percentage of the water holding capacity fo a particular soil, rather than as absolute water content. In recent years, one of the most intensely investigated controls on soil CH$\sb4$ consumption has been its inhibition by NH$\sb4\sp+$-fertilizer. In addition to NH$\sb4\sp+,$ however, I found that other ions inhibited CH$\sb4$ oxidation. In some soils non-NH$\sb4\sp+$ ions were so toxic that they completely masked the NH$\sb4\sp+$ effect. It is crucial, therefore, to control for salt effects when investigating NH$\sb4\sp+$-inhibition. In both field and laboratory experiments, CH$\sb4$ consumption in a birch soil was sensitive to NH$\sb4\sp+$, whereas a spruce soil was unaffected. In the birch soil, NH$\sb4\sp+$ apparently inhibited methanotroph growth, rather than enzymatic CH$\sb4$ oxidation, whereas methanotrophs in the spruce soil were apparently insensitive to NH$\sb4\sp+$. These results suggest that the primary landscape-level control over the response of soil CH$\sb4$ consumption to NH$\sb4\sp+$-fertilization is the cross-site distribution of physiologically distinct CH$\sb4$ oxidizers.
    • Spatial and temporal patterns in the Gulf of Alaska groundfish community in relation to the environment

      Mueter, Franz Josef; Norcross, Brenda L. (1999)
      The GoA supports a rich demersal fish community dominated by gadids, pleuronectids, sablefish (Anoplopoma fimbria) and rockfishes (Sebastes spp.). This study describes the structure of the juvenile and adult groundfish communities of the Gulf of Alaska (GoA) in relation to their environment and along spatial and temporal gradients. Abundance data were obtained from trawl surveys of juvenile groundfishes in the nearshore areas of Kodiak Island (1991--1996), shrimp-trawl surveys in the same areas (1976--1995), and triennial bottom trawl surveys of adult groundfishes on the GoA shelf and upper slope (1984--1996). Species richness, species diversity, total abundance, and multivariate indices of species composition for each station sampled were statistically related to depth, temperature, salinity, sediment composition, geographic location, and time of sampling to identify spatial and temporal patterns in community structure. The observed patterns were then related to local and large-scale atmospheric and oceanographic trends. Both juvenile and adult groundfish communities were primarily structured along the depth gradient. The abundance of juvenile groundfishes decreased with depth from 0 to 100m, whereas the abundance of adults increased with depth to a peak at 150--200m. Species richness and diversity of the adult community had a significant peak at 200--300m. Spatial patterns suggested higher abundances, lower species richness and diversity, and a different species composition of demersal fishes in the western GoA compared to the eastern GoA. These large-scale spatial patterns appear to be related to differences in upwelling between the eastern and western GoA. A 40% increase in total groundfish biomass on the GoA shelf and upper slope was estimated between 1984 and 1996. Significant changes in species composition occurred in the nearshore areas of Kodiak Island in the early 1980s, from a community dominated by shrimp and small forage fishes to one dominated by large piscivorous gadids and flatfishes. The change in species composition in the nearshore community appeared to be linked to an increase in advection in the Alaska Current. Increased flow around the GoA may enhance the supply of nutrients and plankton on the shelf and upper slope, resulting in an increase in overall productivity of the pelagic and demersal biota.
    • The development of diving behavior and physiology in juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica

      Burns, Jennifer Moss; Castellini, Michael (1997)
      The development of diving behavior and physiology in juvenile Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica was studied in order to determine the effects of age, body size, and condition on diving ability. During the austral summers of 1992, 1993, and 1994, the diving behavior of 39 pups and 15 yearlings was monitored using time depth recorders (TDRs). In addition, 26 pups were equipped with satellite-linked time depth recorders (SLTDRs) to track fall and winter diving behavior. Blood samples and morphological measurements were taken at each handling. Pups began to dive within two weeks of birth, and the mean dive depth, duration, and number of dives per day increased significantly over the next 10 weeks. During this period, the ability of pups to regulate physiological processes related to diving increased, as did their aerobic dive limit (ADL). Whereas diving behavior was determined primarily by age rather than mass in young pups, age had little effect on the diving behavior of pups older than 2 months (as determined from SLTDR records). Because seals were not handled after SLTDR deployment, the effects of mass could not be directly modeled in these pups. However, in yearlings, the ADL, and approximately 50% of the variation in dive behavior could be explained by differences in body size. Most dive parameters differed by time of day, and deeper and longer dives were more frequent in the afternoon period. The diel pattern was consistent with the hypothesis that pups were foraging throughout the day on vertically migrating prey species. In yearlings, dive patterns suggested that large individuals foraged primarily on shallow water prey, while smaller animals concentrated on deeper prey such as Antarctic silverfish. Tracking studies revealed that juveniles were capable of long distance movements, but suggested that they remained closer to the coastline than adults. The absence of obvious differences in dive behavior between regions suggested that juveniles were foraging on similar prey throughout the Ross Sea. While scat analyses confirmed this hypothesis, tissue stable isotope ratios suggested that some juveniles were feeding on different prey, or in different areas than adults.
    • The Ecology Of Marten In Southcentral Alaska

      Buskirk, Steven William (1983)
      The ecology of marten in the upper Susitna Basin, southcentral Alaska was studied from January 1980 to June 1982. Data were gathered on home range and movements, seasonal food habits, habitat use and winter energetic strategies. Radio telemetry was used to obtain a total of 560 locations for 17 marten. Mean home range sizes of marten along the Susitna River were 3.71 km('2) for females, 6.82 km('2) for males and 6.75 km('2) for adult males (2+ years). Marten were found to be nocturnal in autumn and to show strong variability in their diel activity patterns in late winter. Marten tended to move upward in elevation during spring and downward in autumn, contrary to the prevailing views of trappers. Analyses of marten scats and colon contents collected during four seasons showed the most important foods to be microtine rodents, squirrels, fruits and birds. Major foods showed strong seasonal variation in utilization. Microtines were most important in autumn and showed declining use over winter. Northern red-backed voles were the most important microtine species. Sciurids were most important in spring and appeared to be a nonpreferred alternative food. Marten made little use of shrews, snowshoe hares, porcupines or insects. Carrion and human foods were highly preferred and consumed when available. Habitat utilization was studied through the use of aerial transects and snow tracking and by identifying resting sites. Marten foraged for microtines more frequently than expected in vegetation types dominated by black spruce. Marten rested in winter primarily in active red squirrel middens in stands dominated by old-growth white spruce. Fat depot and organ weights and total body fat of marten were measured to find an indicator to total body fat. Marten were found to have extremely low body fat ratios which did not show a significant change over winter.