Now showing items 127-146 of 203

• #### Nesting ecology of migratory golden eagles (Aquila chrysaetos) in Denali National Park, Alaska

Between 1988 and 1993 I measured occupancy of nesting territories and reproduction of golden eagles (Aquila chrysaetos) in Denali National Park, Alaska. I collected data occupancy of nesting territories and three reproductive variables (pairs nesting, pairs producing fledglings, and fledgling production) at 74 nesting territories using three aerial surveys each year. During my study, annual fledgling production varied nearly threefold, from 20 fledglings in 1992 to 58 fledglings in 1989. Although rates of nesting territory occupancy did not vary significantly among years (yj = 8.21, d.f. = 5, P = 0.114), I noted significant variation in the proportion of pairs laying eggs (X2 = 33.12, d.f. = 5, P < 0.001) and the proportion of pairs fledging young (X2 = 16.03, d.f. = 5, P = 0.007) among years. Decreases in pairs laying eggs were correlated with decreases in average daily numbers of snowshoe hare (Lepus americanus) and willow ptarmigan (Lagopus lagopus) observed in the study area (rs = 0.83, P = 0.04).
• #### New 3-d video methods reveal novel territorial drift-feeding behaviors that help explain environmental correlates of Chena River chinook salmon productivity

Chinook salmon (Oncorhynchus tshawytscha) are critical to subsistence and commerce in the Yukon River basin, but several recent years of low abundance have forced devastating fishery closures and raised urgent questions about causes of the decline. The Chena River subpopulation in interior Alaska has experienced a decline similar to that of the broader population. To evaluate possible factors affecting Chena River Chinook salmon productivity, I analyzed both population data and the behavior of individual fish during the summer they spend as fry drift feeding in the river. Using a stereo pair of high definition video cameras, I recorded the fine-scale behavior of schools of juvenile Chinook salmon associated with woody debris along the margins of the Chena River. I developed a software program called VidSync that recorded 3-D measurements with sub-millimeter accuracy and provided a streamlined workflow for the measurement of several thousand 3-D points of behavioral data (Chapter 1). Juvenile Chinook salmon spent 91% of their foraging attempts investigating and rejecting debris rather than capturing prey, which affects their energy intake rate and makes foraging attempt rate an unreliable indicator of foraging success (Chapter 2). Even though Chinook salmon were schooling, some were highly territorial within their 3-D school configurations, and many others maintained exclusive space-use behaviors consistent with the population regulatory effects of territoriality observed in other salmonids (Chapter 3). Finally, a twenty-year population time series from the Chena River and neighboring Salcha River contained evidence for negative density dependence and a strong negative effect of sustained high summer stream discharge on productivity (Chapter 4). The observed territoriality may explain the population's density dependence, and the effect of debris on foraging efficiency represents one of many potential mechanisms behind the negative effect of high stream discharge. In combination, these findings contribute to a statistically and mechanistically plausible explanation for the recent decline in Chena River Chinook salmon. If they are, in fact, major causes of the decline (other causes cannot be ruled out), then we can be tentatively hopeful that the population may be experiencing a natural lull in abundance from which a recovery is possible.
• #### Nutritional and ecological determinants of growth and reproduction in Caribou

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.
• #### Phylogeography and population genetics of northern flying squirrels (Glaucomys sabrinus) in Southeast Alaska

The Prince of Wales flying squirrel (Glaucomys sabrinus griseifrons), a forest associated species, is endemic to several islands in the Alexander Archipelago of Southeast Alaska. Mitochondrial and nuclear markers were examined to assess the genetic uniqueness of this subspecies and its geographic extent and to investigate gene flow among island and mainland populations of flying squirrels. Data from both sets of markers are congruent, and agree with the subspecific designation. The data also indicate that the Prince of Wales subspecies is isolated from other populations in Southeast Alaska, but that there may be gene flow among islands on which it occurs. This island lineage is likely the result of a founder event after the retreat of the Pleistocene ice sheets. The fact that this subspecies is isolated and divergent from mainland populations has potential implications for the design and planning of timber harvests on these islands.
• #### Physiological and ecological determinants of nutrient partitioning in caribou and reindeer

The effects of season, migration, and reproduction on the adipose and protein dynamics of barren-ground caribou were determined from field collections of adult females from the Porcupine Herd. Radio-collared females recaptured over time provided data on animals of known reproductive status. Pregnant females averaged a daily loss of 50g body fat and 15g body protein during the last 60 days of gestation. Between June and September, lactating females preferentially deposited body protein but non-lactating females preferentially deposited body fat. In both cohorts, fat deposition increased relative to protein deposition in fall, but maximum fat deposition occurred in summer. Females that conceived averaged 220% more body fat and 17% more body protein than females that did not conceive. Fetal and birth weight positively correlated with maternal protein reserves, but not with maternal fat reserves. Fieldwork on free-ranging caribou were complemented with nutritional experiments on captive animals to determine the effects of energy intake, protein intake, the dietary protein:energy ratio, date, and body condition on nutrient partitioning between fat and protein deposition, and between maternal tissue deposition and milk production. In both lactating and non-lactating females, the proportion of tissue deposited as fat rather than protein increased between spring and fall but decreased with increasing fatness. Lactating and non-lactating females had comparable efficiency coefficients for net energy retention (60% and 65% respectively), but daily maintenance requirement for lactating females (456 KJ/BW$\sp{0.75}$) was twice that for non-lactating individuals (233 KJ/BW$\sp{0.75}$). Energy intake increased protein deposition in lactating females but increased fat deposition in non-lactating females. Production of milk dry matter, fat, and energy were unaffected by maternal energy intake, maternal protein intake, maternal body condition, or calf age. However, production of milk lactose correlated with maternal energy intake, while production of milk protein correlated with the maternal dietary protein:energy ratio. Prediction equations for body weight and composition of barren-ground caribou were developed using bone, muscle, fat, and organ indices. Prediction equations for body weight were validated with an independent data set.
• #### Population and habitat analyses for Dall's sheep (Ovis dalli) in Wrangell-St. Elias National Park and Preserve

We summarized and statistically analyzed historical fixed-wing aerial surveys (1949-2002) and harvest records (1983-2002) of Dall's sheep (Ovis dalli dalIi) from Wrangell-St. Elias National Park and Preserve (WRST). Among survey units there were significant differences in observed densities, hunter-reported harvest, horn lengths of harvested rams, and horn length residuals from the regression of length on age. There was no consistent evidence of net change in WRST-wide sheep density, even though some survey units showed trends in density. Reported harvest in WRST declined linearly during 1973-2003 from 376 to 139 rams per year. We estimated the relationships among population and habitat characteristics with multiple linear regression. We standardized all variables and evaluated all 1, 2, and 3 variable models using Akaike's Information Criterion for small sample sizes (AICc) for model selection. The best model for sheep density showed a positive correlation with median NDVI (relative vegetation greenness) and terrain ruggedness. The same model resulted from examining adult and Iamb cohorts separately. Approximately 50% of horn length was explained by age. The habitat variables estimated did not explain a significant amount of the variance observed in reported harvests or horn length residuals from the regression of length on age.

• #### Population dynamics of tundra swans on the lower Alaska Peninsula

This study was initiated in response to concerns regarding apparent declines in abundance and breeding pair density of tundra swans on and adjacent to Izembek National Wildlife Refuge (NWR) on the lower Alaska Peninsula. I conducted an analysis of long-term data (1978-1996) to estimate demographic parameters and assess the relationship between survival probabilities and a number of environmental and ecological factors. Rates of productivity (egg, nest, cygnet survival) and annual rates of apparent adult survival were lower and more variable than previously observed for other swan populations and species. A negative relationship between nesting success and brown bear density indicates that depredation by bears is a primary determinant of tundra swan reproductive success. Changes in apparent survival probability were primarily influenced by high and variable rates of permanent emigration. Because of low rates of production and apparent survival, immigration by swans from other breeding areas may be important for sustaining a breeding population of tundra swans on and adjacent to Izembek NWR.
• #### Population ecology of Pacific common eiders on the Yukon-Kuskokwim Delta, Alaska

Knowledge of ecological factors that influence birth, death, immigration, and emigration provide insight into natural selection and population dynamics. Populations of Pacific common eiders (Somateria mollissima v-nigrum) on the Yukon-Kuskokwim Delta (YKD) in western Alaska declined by 50-90% from 1957 to 1992 and then stabilized at reduced numbers from the early 1990's to the present. This study investigates the primary underlying processes affecting population dynamics of Pacific common eiders, with the goals of understanding factors that may have led to the observed decline and subsequent stabilization, and providing tools from which conservation, management, and recommendations for future research can be drawn. I examined variation in components of survival and reproduction in order to test hypotheses about the influence of specific ecological factors on life history variables and to investigate their relative contributions to local population dynamics. These analyses include data I collected from 2002 to 2004, in addition to historical data collected from 1991 to 2001. Apparent survival of adult females was high and relatively invariant, while components of reproduction were low and variable, both within and among individuals. Timing of nesting and seasonal declines in clutch size and nest survival indicated that females in the early and mid parts of the breeding season produced the highest numbers of offspring; suggesting directional selection favoring early nesting. Probability of a nest containing [1 or less] nonviable egg was positively related to blood selenium concentrations in hens, but no other contaminant-related reductions to life history variables were found. All estimates of population growth ([lamda]) indicated that the YKD population was stable to slightly increasing during the years of the study (range [lamda]: 1.02-1.05 (CI: 0.98-1.11)), and would respond most dramatically to changes in adult female survival. However, historical fluctuations in [lamda] were primarily explained by variation in reproductive parameters, particularly duckling survival. Practical options for increasing adult survival currently may currently be limited. Thus, enhancing productivity, particularly via methods with simultaneous positive effects on adult survival (e.g., predator removal), may offer a more plausible starting point for management aimed at increasing population growth.
• #### Population status and patterns of distribution and productivity of kittiwakes on St. George Island, Alaska

I studied populations, distributions, and reproductive performance of red-legged and black-legged kittiwakes on St. George Island in the summers of 1993-1995, where populations of both species have experienced generally poor reproductive performance and population declines of ca. 40% over the past 20 years. In 1995, I conducted a whole-island census of kittiwakes on St. George Island and found estimated breeding populations of 193,930 red-legged kittiwakes (81% of their global population), and 62,568 black-legged kittiwakes. In addition, I analyzed census trends on 51 land-based census plots on St. George Island and found that numbers of both species have stabilized in recent years. I experimentally evaluated the hypothesis that nesting red-legged kittiwakes on St. George Island are competitively displaced by larger-bodied black-legged kittiwakes to narrower rock ledges and higher elevations. I determined nest-site preferences of both species by attaching narrow and wide artificial nesting ledges within high-and low-elevation areas of St. George Island and found no evidence of competitive displacement: red-legged kittiwakes preferred narrow ledges, black-legged kittiwakes preferred wide ledges, and both species preferred ledges in areas where conspecifics nested at high density. Multiple regression analyses suggested that kittiwakes breed earlier and more successfully in summers preceded by cold winters and that inter-annual variability in kittiwake breeding success was unrelated to weather conditions during the breeding season itself. These results suggest that winter weather has indirect effects on breeding kittiwakes by influencing prey abundance several months later. Furthermore, strong winds impaired growth rates of kittiwake chicks in exposed nest sites and the growth of black-legged kittiwake chicks relative to red-legged kittiwake chicks. I identified two prominent patterns of within-colony spatial variability in kittiwake productivity and suggest that patchy "bird quality" or localized "information neighborhoods" may be responsible because traditional explanations do not apply. The "information neighborhood" is a new hypothesis which proposes that individuals are influenced by the breeding status of neighbors because their status represents an additional source of information about current breeding conditions that can be used to better tailor parental investment.
• #### Postbreeding Ecology Of Shorebirds On The Arctic Coastal Plain Of Alaska

Previous research on the Arctic Coastal Plain (ACP) of Alaska has shown that postbreeding shorebirds congregate at coastal sites prior to fall migration. Relatively little has been done to compare distribution, community characteristics, or behavior broadly across the ACP landscape, but this information is necessary to set the context for interpreting population demographics and setting conservation priorities. I collected data on distribution, species composition, phenology, and habitat use of postbreeding shorebirds in 2005--2007. I found that distribution of shorebirds across the ACP was not uniform: I identified persistent "hotspots" at Peard Bay, Pt. Barrow/Elson Lagoon, Cape Simpson, Smith Bay to Cape Halkett, and at the Sagavanirktok and Kongakut Deltas. Staging phenology varied by species and location, and differed than that reported in previous studies for several species. Three foraging habitat guilds existed with birds favoring gravel beach, mudflat, or salt marsh/pond edge habitats. Using VHF telemetry. I examined how shorebirds moved from tundra breeding sites to and between coastal postbreeding sites. I found that most species exhibited a variable direction of movement compared to their ultimate migration direction; this may be related to each species' overall length of stay on the ACP. I also found species-specific patterns of movements and residence time that were indicative of differing life history strategies. Lastly, I examined the use of physiological tools (triglyceride and corticosterone levels) to assess function and quality of foraging sites for postbreeding shorebirds, taking into account varying molt strategies. I determined that molt strategies affected physiological profiles and physiologic metrics varied through space and time. However, my hypotheses for variation in physiological patterns for shorebirds employing different molt strategies and using sites of varying quality were not completely upheld. I suggest that assessments of site quality for postbreeding shorebirds should consider species-specific life history strategies, and use multiple species and physiological metrics as indicators. Given suspected declines in North American shorebird populations, and accelerated rates of environmental change in northern Alaska, this contextual information regarding postbreeding distribution, population characteristics, behavior, and physiology may help interpret changes in shorebird populations or behavior and establish strategies to protect important habitat.
• #### Potential muskox habitat in the National Petroleum Reserve-Alaska: a GIS analysis

Muskoxen (Ovibos moschatus), reestablished in northern Alaska in recent decades, have been increasing in number and distribution. However, their selection of habitat within the landscape, historically and presently, remains inadequately documented. This project produced maps of predicted muskox habitat in the National Petroleum Reserve-Alaska (NPR-A), that provide a basis for management of muskoxen and protection of their habitat in relation to proposed oil, gas and mineral exploration. Vegetation analyses showed compositional differences and interactions between vegetation and terrain. Within a geographical information systems (GIS) database, muskox locations, satellite-based vegetation maps and terrain data for the Kuparuk River drainage basin were assimilated, and a maximum likelihood classification developed to produce a habitat selection model incorporating the interactive effects of these characteristics. Using NPR-A GIS data, the model was extrapolated to produce maps showing suitable summer habitat in lower-lying drainages and wetter areas, and suitable winter habitat in drier, more rugged, exposed areas.
• #### Prefledging survival and reproductive strategies in black brant

We develop a general model useful for estimating survival of young waterfowl between hatching and fledging. Our model allows for interchange of individuals among broods and relaxes the assumption that individuals within broods have independent survival probabilities. We consider point estimation of survival rates and corresponding variances of the point estimators. We estimated gosling survival of black brant (Branta bernicla nigricans) during summers of 1987-89 on the Yukon-Kuskokwim Delta, Alaska. Eight-two percent of females radio-marked at hatch fledged at least 1 gosling (brood success). Survival of goslings within broods was estimated by 3 methods: (1) changes in mean brood size through time, (2) observation of goslings associated with marked adults, and (3) age ratios of brant captured in banding drives. Estimates of survival within successful broods averaged 77% and ranged from 57 to 90%. Combining brood success and survival of young within broods yields estimates of overall gosling survival which averaged 64% and ranged from 77% in 1987 to 52% in 1989. We analyzed variation in egg size of black brant in relation to clutch size, laying date, female age, year, and position in the laying sequence. Egg size increased with clutch size and female age, and decreased with laying date, year, and position in the laying sequence. We did not detect a negative phenotypic correlation between clutch size and egg size. However, overlap in total clutch volumes for clutches of different sizes indicated trade offs occurred among individuals with comparable investments in their clutches. We web-tagged black brant goslings at hatch, recorded their egg size, position in the egg-laying sequence, initial brood size, hatch date, and nesting density and examined the effect of these characteristics on their probability of recapture. Larger broods from larger eggs, and with earlier hatch dates were more likely to be recaptured. There was a tendency for young females to be less successful in rearing their broods; however, this may be related to their egg size, initial brood size, and hatch date, rather than age per se.
• #### Production of vascular aquatic plants in wetlands of Alaska: A comparative study

I examined the effects of climate and hydrology on aboveground biomass of macrophytes in wetlands across Alaska by investigating the effects of latitude, July mean air temperature, lake type (open, periodically inundated, and closed), hydrology, and water and sediment chemistry on emergent and submersed vascular plant biomass to determine environmental variables that influenced wetland plant growth. I sampled aboveground biomass of macrophytes in four wetland complexes within Alaska: Kenai and Tetlin National Wildlife Refuges, Minto Flats State Game Refuge, and the Arctic Coastal Plain near Prudhoe Bay, Alaska. In addition to peak aboveground biomass, I also collected water and sediment samples from each lake that were analyzed for water temperature, color, alkalinity, turbidity, pH, orthophosphate, $\rm NO\sb3/NO\sb2$-N, NH$\sb4\sp+$, and total sediment C, N, and P. I found a quadratic relationship between emergent plant biomass and latitude. Minto, the second most northern site, had the greatest plant biomass, Prudhoe Bay, the most northern site had the least, and Kenai and Tetlin had moderate levels of biomass. I found a positive linear relationship between emergent plant biomass and July mean temperature, suggesting that on-site summer condition is important in predicting biomass. Submersed plant biomass was better related to alkalinity, turbidity and sediment P than to latitude, which suggests that climate is not as important in predicting submersed plant biomass as it is in predicting emergent plant biomass. Emergent plant biomass differed spatially and temporally, while submersed plant biomass showed no distinct patterns in variation across the landscape and with changes in hydrologic input. Many water and sediment chemistry variables differed among lake types and between flood regimes. Emergent plant biomass was associated with changes in water level as well as changes in water. Plant species composition differed among lake types and tended to change with flood regime as well. A separate suite of species occupied closed lakes, while open and periodically inundated lakes tended to contain more similar plant species. Both climate and hydrology appear to have a significant impact on emergent and submersed plant biomass and species composition in wetlands of Alaska. These spatial and temporal differences have direct influences on secondary producers living in wetlands of Alaska.
• #### A protocol for assessing the impacts of urbanization on coho salmon with application to Chester Creek, Anchorage, Alaska

Coho salmon (Oncorhynchus kisutch) abundance has declined in many urban streams. The causes of these declines can be hard to identify because urban impacts on stream ecology are complex and can vary between watersheds. This makes it difficult to develop appropriate and effective strategies for stream rehabilitation or mitigation aimed at increasing coho productivity. To improve this situation I developed a habitat quality assessment protocol for urban coho salmon to help identify significant habitat degradation as a prelude to restoration planning. To evaluate the protocol I used it to assess coho habitat quality in Chester Creek, Anchorage, Alaska, an urban stream that once supported a large population of coho salmon but now only supports a remnant population. I compared habitat characteristics from one non-urban and two urban study reaches to 'healthy' standard guidelines. This application of the protocol showed that the most significant adverse effects of urbanization on coho salmon habitat in urbanized reaches were increased flood intensity, barriers to adult and juvenile migration, reduced physical habitat complexity, siltation of spawning gravels, stressful water quality conditions, and stocking of potential predators and competitors. These results provide useful information for prioritizing rehabilitation and mitigation efforts in Chester Creek.
• #### Proximate and ultimate control of reproductive effort in northern shovelers (Anas clypeata) nesting at Minto Flats, Alaska

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.
• #### Range, movements, population, and food habits of the Steese-Fortymile caribou herd

The Steese-Fortymile caribou (Rangifer arcticus stonei Allen) form one of the most economically important herds in Alaska. This study of the herd took place from September, 1952, to December, 1955, under the auspices of the Alaska Cooperative Wildlife Research Unit at the University of Alaska and of the Federal Aid in Wildlife Restoration branch of the United States Fish and Wildlife Service, Project W3R. The Steese-Fortymile range occupies about 35,000 square miles of east-central Alaska and the Yukon Territory, lying mainly between the Tanana and Yukon Rivers. The terrain is mountainous, but not rugged; roads and towns are scarce, and a maximum of 60,000 people live on the fringes. Seven major plant communities comprise the range vegetation, three of them covering 60 to 70 per cent of the area and furnishing the bulk of the food for caribou. The carrying capacity is computed to be 70,000 to 90,000 caribou. The erratic and continual movements of caribou characterize this game species. Their movements vary from day to day and season to season. Most of the traveling takes place during the early morning and late afternoon; major seasonal movements take place in the spring and fall. Past and present data provide a general picture of the movement pattern of this herd throughout the year. The Steese-Fortymile herd dwindled from a peak of about 500,000 animals in the late 1920's to a low of 10,000 to 20,000 in the early 1940's. The decline is attributed to a population shift. The present population contains at least 50,000 animals and is increasing steadily. Reproduction was high during the years 1950 to 1955. The rut takes place during the first two weeks of October; most of the calves are born during the latter half of May, following a gestation period of about 33 weeks. Valuable information on caribou behavior during the calving period is presented. Counts taken in May show that at least 50 per cent of the calves survive the first year. Wolf and man are the most important mortality factors affecting this herd. The total annual mortality, excluding calves, is estimated at eight per cent. Sex and age data from composition counts and hunter-checking-station operations indicate that this herd is young and that the sex ratio approaches 100:100. The annual increment for the herd is computed to be 10 to 15 per cent. Caribou are cursory feeders and eat a wide variety of plants. The main periods for resting and feeding occur during the middle portions of the day and night. The caribou’s diet hinges upon the available food supply, and thus varies with the seasons. In winter, the diet consists mostly of lichens, grasses, and sedges, with browse plants of some importance; data from 23 stomach-samples are presented. In spring, the new shoots of willow, dwarf birch, grass, and sedge are most important; information is based only on field observations. In summer, a wide variety of plants are eaten; willow and dwarf-birch foliage are of greatest importance, followed closely by grasses and sedges; data from 27 stomach-samples are presented. In fall, the diet shifts from a predominance of woody plants and fungi in late August to one of lichens, grasses, and sedges in late September; data from 70 stomach-samples are presented. The problems of data-gathering are discussed, as related to management practices. The contributions made by this report are outlined, and the important information still needed for proper caribou management is listed.