Poor Mast Research Articles

Contribution of Acorn Masting to Food Composition and Body Condition of and Crop Damage by Wild Boars (Sus scrofa) Inhabiting Evergreen Forests in Japan

We analyzed the stomach contents of wild boars (Sus scrofa) inhabiting evergreen forests in western Japan and found that they were dependent on the masting of acorns of Castanopsis cuspidata. The increased availability of C. cuspidata acorns positively affected their consumption by wild boars. In the good mast years, wild boars consumed C. cuspidata acorns from November to June of the following year. No significant annual variation in body condition was detected, suggesting that alternative food resources (e.g., bamboo shoots) may have maintained the body condition of wild boars, even in poor mast years. A strong negative correlation was found between the consumption of C. cuspidata acorns and the amount of crop damage to vegetables. This study revealed the wild boar as a pulsed food resource feeder, which has not yet been identified in Japan, and emphasized the importance of considering C. cuspidata masting for designing effective strategies for mitigating crop damage.

Brown bear feeding habits in a poor mast year where supplemental feeding occurs

The diet of free-ranging bears is an important dimension regarding their ecology, affecting their behavior, population structure, and relation with humans. In Croatia, there has been no recent study on the natural food habits of brown bears (Ursus arctos) or the influence of artificial feeding sites on their diet. During 2017, we collected 53 brown bear stomachs from bears in 2 regions of Croatia—Gorski Kotar and Lika—to assess their diet. Plants—Allium ursinum, the Poaceae family, Cornus mas, berries (i.e., Prunus avium, Rubus plicatus), beechnuts (Fagus spp.)—and various plant parts (i.e., dry leaves, buds, conifer needles, and twigs), as well as mushrooms, made up 80% of the percentage of the volume (%V) of all consumed items. Corn (Zea mays) from the feeding sites made up 37% of the bears' diet (%V), whereas 20% (%V) was meat and 14% (%V) was pome fruits. Scavenged or preyed animal species, such as wild boar (Sus scrofa), horse (Equus caballus), domestic pig (S. scrofa domesticus), cattle (Bos taurus), roe deer (Capreolus capreolus), and small mammals comprised >66% of %FO (frequency of occurrence), but only 20% of %V. Our results showed that food resources (i.e., livestock such as horses, cattle, and pigs, and corn) found at supplemental feeding sites were more frequently chosen by bears than natural food in 2017, a year characterized by almost no beechnut crop. The results showed that subadult bears obtained most food from feeding sites. These 2 patterns suggested that bears may focus on artificial feeding sites to find food in years when natural food sources are depleted, although this should be tested using diet and food availability data collected from several years.

Climate and tree seed production predict the abundance of the European Lyme disease vector over a 15-year period

BackgroundTo predict the risk of tick-borne disease, it is critical to understand the ecological factors that determine the abundance of ticks. In Europe, the sheep tick (Ixodes ricinus) transmits a number of important diseases including Lyme borreliosis. The aim of this long-term study was to determine the abiotic and biotic factors driving the annual abundance of I. ricinus at a location in Switzerland where Lyme borreliosis is endemic.MethodsOver a 15-year period (2004 to 2018), we monitored the abundance of I. ricinus ticks on a monthly basis at three different elevations on Chaumont Mountain in Neuchâtel, Switzerland. We collected climate variables in the field and from nearby weather stations. We obtained data on beech tree seed production from the literature, as the abundance of Ixodes nymphs can increase dramatically two years after a masting event. We used AIC-based model selection to determine which ecological variables drive annual variation in tick density.ResultsWe found that elevation site, year, seed production by beech trees two years prior, and mean annual relative humidity together explained 73.2% of the variation in our annual estimates of nymph density. According to the parameter estimates of our models, (i) the annual density of nymphs almost doubled over the 15-year study period, (ii) changing the beech tree seed production index from very poor mast (1) to full mast (5) increased the abundance of nymphs by 86.2% two years later, and (iii) increasing the field-collected mean annual relative humidity from 50.0 to 75.0% decreased the abundance of nymphs by 46.4% in the same year. Climate variables collected in the field were better predictors of tick abundance than those from nearby weather stations indicating the importance of the microhabitat.ConclusionsFrom a public health perspective, the increase in nymph abundance is likely to have increased the risk of tick-borne disease in this region of Switzerland. Public health officials in Europe should be aware that seed production by deciduous trees is a critical driver of the abundance of I. ricinus, and hence the risk of tick-borne disease.

Age- and Sex-Associated Differences in the Diet of the Asian Black Bear: Importance of Hard Mast and Sika Deer

In the context of reducing human–bear conflict, understanding potential foraging variation within a bear population yields insights into differences in foraging strategy according to an individual's sex and age. Stable isotope analyses reveal information regarding assimilated dietary components. To confirm the foraging variation of Asian black bears and assess its underlying factors, we conducted stable isotope analysis of hair samples. We constructed linear mixed-effect models to examine the effects of sex, age, and hard mast abundance on bear diet. Furthermore, we used stable isotope data on food resources to estimate bear diets from isotopic mixing models to evaluate differences in dietary components among age–sex classes. During the reproductive season, δ15N values were positively correlated with bear age, and dietary deer fraction was the highest for adult males. Our results also showed that during the hyperphagia season, bears were mostly dependent on hard mast, regardless of its abundance. However, δ15N values of bears were higher during poor mast years than when mast was plentiful, thus implying that bears consume increased proportions of deer and/or insects (e.g., Vespidae) in poor mast years. Our results indicate that feeding strategies in Asian black bears differ according to age–sex classes and seasons.

Summarizing Colorado's black bear two‐strike directive 30 years after inception

ABSTRACTColorado Parks and Wildlife implemented a new statewide management policy in 1985 for nuisance black bears (Ursus americanus), known today as the 2‐strike directive. It allowed wildlife managers to assess the repeatability of nuisance bear behavior after translocating them to quality bear habitat away from human food sources. We evaluated this directive using 30 years (1987–2016) of nuisance black bear capture records. Statewide, 53% of 1,093 bears caught, marked, and moved (1st strike) were never reported again, while 25% were killed for a 2nd strike, and hunters harvested 17%. Subadult males committed 2nd strikes more quickly than adult males and females. Although time between strikes was greatest for adult females (496 days), they had the largest probability of committing a 2nd strike among all cohorts. We found that the number of 1st strike captures, from late summer through fall was greatest during years of poor mast production. We suggest that the 2‐strike policy has been an effective management tool for nuisance black bears in Colorado, USA, because of low rates of nuisance behavior following 1st‐strike translocation. If a state or local management objective is to increase black bear populations, wildlife managers may increase tolerance of adult bears that have received their 1st strike in years when fall mast crops largely fail because they are less likely to commit a 2nd strike. Lower tolerance of subadult males may be warranted in bad food years, especially in areas where reductions in bear populations are desired, because they tend to repeat nuisance behaviors more quickly than other bears. © 2019 The Wildlife Society.

Estimating the seasonal energy balance in Asian black bears and associated factors

AbstractEnergy balance (i.e., energy intake minus energy expenditure) is an essential factor when evaluating an animal's nutritional state. We aimed to identify periods of the year that are most important for Asian black bears (Ursus thibetanus) in terms of energy balance. We estimated bears’ daily energy balance by estimating energy intake based on the energy content (kcal/g) of major food items, their average ingestion rate (g/min), and daily feeding time (min) and by estimating energy expenditure using an equation for the costs of resting, traveling, and feeding based on behavioral data of 34 bears fitted with GPS collars in central Japan. Because food habits of bears change seasonally, we estimated daily energy balance for each month. And, because bears change their feeding behavior depending on the availability of hard mast, we made separate estimations for years of good and poor mast conditions during autumn. We identified major food items from fecal analysis and calculated the gross energy content per unit for each item. Based on direct observation of bears feeding over 10 yr, we measured ingestion rates of the major food items; Quercus crispula acorns on the tree had the highest ingestion rate, whereas the values of other items did not show notable characteristics. The variability of energy expenditure rose moderately in good mast years, except for males. On the other hand, there was a bimodal pattern of energy intake and energy balance, declining from May to July, rising again from August to October, and declining in November. The peak of energy intake and energy balance was larger in good mast years than in poor mast years only for females, whereas the cumulative energy balance in good mast years was larger than in poor mast years for both sexes. After poor mast years, the cumulative energy balance of males becomes negative in February, during hibernation, and did not exceed zero until August, even if they could start feeding in May. Thus, further longitudinal studies that examine cumulative energy balance, rather than energy balance alone, are necessary to clarify the seasonal change in the nutritional state of Asian black bears.

Does hard mast production affect patterns of cementum annuli formation in premolar teeth of Asian black bears (Ursus thibetanus)?

Cementum annuli widths in mammals are is influenced by the nutrition of mammals. Reproductive stress has been is suggested to reduce the width of lead to narrower cementum annuli widths in female Asian black bears (Ursus thibetanus); however, food availability in autumn strongly impacts bear nutrition and likely impacts cementum widths as well. This study aimed to test how cementum annuli widths and the formation of false annuli were influenced by hard mast production. We established two hypotheses: (1) cementum annuli widths become narrower in poor mast years owing to inadequate nutritional conditions and (2) false annuli occur more frequently in poor mast years. We used teeth samples from male bears to avoid reproductive influences and separated width data into “adult” and “subadult” groups. We calculated the proportional width index (PWI) and used linear mixed models to estimate the masting effects on PWI. Generalized linear mixed models estimated the masting effects on false annuli frequency. True annuli widths and false annuli formation showed no significant relationship with mast production in adults. In subadults, poor mast production weak negative influence on false annuli formation. These new data resolve previous questions, allowing us to deduce that cementum annuli widths are a reliable index of reproductive success in female bears.

Using a novel method of potential available energy to determine masting condition influence on sex-specific habitat selection by Asiatic black bears

Abstract Habitat selection is assumed to accrue fitness benefits. Where resource availability is variable, individuals should respond by changing habitat selection to increase resource availability. However, direct links between observed changes in habitat selection and energetic benefits of this behavior are rarely detected. We used a novel method whereby we converted interannual production levels of three hard-mast-producing Fagaceae species into a comparative energetic productivity score to investigate potential energetic benefits of Asiatic black bear habitat selection. We captured and fitted GPS collars on 19 bears between 2006 and 2010 in the Ashio-Nikko Mountains, Japan. We also collected data on hard-mast production and integrated these data with fine-scale vegetation maps. Then we mapped the potential available mast energetic production for each vegetation type to evaluate their potential energetic benefit for bears. Habitat use differed between poor and good mast years. Bears mostly used Japanese oak in good mast years, and there were sexual differences in September of poor mast years; females used mostly Japanese oak, whereas males used Konara oak. In those years, bears may have benefitted energetically by changing habitat use; however, the mean potential available energy to bears never exceeded that in good mast years, even if they used different habitats.

Effect of mast production on home range use of Japanese black bears

AbstractAlthough bears may expand their home ranges in times of low food availability, it is unclear what mechanisms directly affect home range extension in times of low mast production in Japanese forests. To clarify the relationship between home range utilization by Japanese black bears (Ursus thibetanus) and abundance and distribution of mast production, we collected data on habitat use from 13 bears (6 M and 7 F) fitted with Global Positioning System (GPS) collars equipped with activity sensors in the Ashio‐Nikko Mountains on the eastern part of Honshu Island, Japan, during 2006–2008. We also collected data on mast production by 5 Fagaceae species. We categorized each fall as either poor (2006) or relatively‐good (2007 and 2008) based on mast production. Bears used small patches in their large home ranges and the distances between core areas increased in the fall of 2006, when the mast of Japanese oak (Quercus crispula) were poorly distributed. Our findings suggest that localized patches of Japanese oak are the staple food for bears in our study area, even in poor mast years. However, in the fall of 2006, we also found that bears moved to lower elevations, relative to 2007 and 2008, in search of alternative foods (e.g., Konara oak [Q. serrata] and Japanese chestnut [Castanea crenata]), which were mostly at lower elevations and produced mast consistently over the study period. Our results suggest that dispersion and elevational distribution of mast‐producing trees affect bear habitat use in fall, as well as amount of mast. © 2011 The Wildlife Society.

Modelling with uncertainty: Introducing a probabilistic framework to predict animal population dynamics

Predictive population models designed to assist managers and policy makers require an explicit treatment of inherent uncertainty and variability. These are particular concerns when modelling non-native and reintroduced species, when data have been collected within one geographical or ecological context but predictions are required for another, or when extending models to predict the consequences of environmental change (e.g., climate or land-use). We present an aspatial, probabilistic framework of hierarchical process models for predicting population growth even when data are sparse or of poor quality. Insight into the factors affecting population dynamics in real landscapes can be provided and Kullback–Leibler distances are used to compare the relative output of models. This flexible yet robust framework gives easily interpretable results, allowing managers as well as modellers to invalidate anomalous models and apply others to real-life scenarios. We illustrate the framework’s power with a meta-analysis of European wild boar ( Sus scrofa) data. We test hypotheses about the effect of geographic region, hunting and mast years on wild boar population growth, to build models of wild boar dynamics for the UK. The framework quantifies the importance of hunting pressure as a driver of population growth, and confirms that reproductive success is greatly decreased in poor mast years, suggesting that the key to predicting wild boar dynamics is to ascertain local hunting pressure and to better understand changing food availability. Geography had no significant effect, indicating that it is not a good proxy for modelling the impact of change in climate or land-use on wild boar populations at the European scale. We use the framework to predict population abundance 9 years after an isolated population of wild boar established in the UK; in a comparison with the only field data and two independent modelling exercises, our framework provides the most robust and informative results.

Acorn Production and Winter Reproduction in White-footed Mice (Peromyscus leucopus) in a Southern Piedmont Forest

Abstract Previous studies of the relationship between acorn production and Peromyscus populations have been conducted in regions with severe winter climate where winter breeding is rare. I trapped white-footed mice, Peromyscus leucopus, in a southern Piedmont oak-hickory forest during autumn and winter for four consecutive years to determine how acorn availability influences winter reproduction in P. leucopus. Acorn production in years 1 and 4 of the study was over 10 times higher than in years 2 and 3. Peromyscus leucopus density was highest in winters following large mast crops, but also increased following a low mast crop in year 3. Body weight was significantly lower during one of the poor mast years, but not the other. More than 50% of female mice were reproductively active during all four winters of the study. Thus, P. leucopus responded positively to high mast availability, but mice remained reproductively active even in poor mast years.

Movements of Allegheny Woodrats in Relation to Timber Harvesting

The Allegheny woodrat (Neotoma magister) occurs in the Appalachian Mountains, forming colonies in rock outcrops, cliffs, and caves. Populations on the northern and western peripheries of the range have experienced drastic declines in the past 20-30 years. Dependence upon rock outcrops makes Allegheny woodrats vulnerable to land-use practices that alter habitats surrounding colonies. To examine the impacts of timber harvesting on Allegheny woodrat behavior, we radiotracked 37 adults during summer 1998 and 1999 in clearcut, diameter-limit, and intact forest stands in the central Appalachians of West Virginia. Home range size and foraging movements generally,were greatest at diameter-limit sites and smallest in intact forests in 1998, following a poor mast crop. We detected no differences among harvest methods in 1999 when mast was abundant. We believe that when hard mast was scarce, woodrats increased foraging movements and home range size to locate mast or sufficient alternative foods. Additionally, woodrats used clearcut and adjacent forested areas in proportion to availability. Our results suggested that clearcutting has minimal impact on woodrat movements, home range, and habitat use if sufficient intact forest is retained adjacent to colonies. Harvesting methods that selectively remove important mast-producing species may represent the greatest disturbance to Allegheny woodrats from forest management.

Influences of Forest Type, Stand Age, and Weather on Deer Weights and Antler Size in the Southern Appalachians

Abstract We analyzed correlations of forest type, age structure, and site index data with weights and antler characteristics of yearling white-tailed deer (Odocoileus virginianus) bucks from specific localities in the Chattahoochee, Cherokee, Nantahala, and Pisgah national forests in Georgia, Tennessee, and North Carolina. Areas in the northern part of the study region produced larger deer with larger antlers than those in the southern portion of the region. These northern areas differed from those to the south in having more diverse ownership and land use and in origins of deer stock. Weights and antler characteristics were significantly correlated (P < 0.05) with percent area in the cove hardwood type, but otherwise were poorly correlated with forest stand type and site index. Percent area in young (0-8 yr old) cove hardwood and in mid-successional (9-20 and 21-40) cove hardwood, pine (Pinus spp.), and upland oak (Quercus spp.) were significantly correlated (P < 0.05) with deer variables, particularly in years following a poor mast crop. Much of the quantifiable habitat influences on deer in the Southern Appalachians probably is masked by low deer densities and the small site quality differences among areas examined. Because much of the forest consists of mature mast-producing oaks and abundant forage is produced in both mature and younger aged stands, deer numbers seem to be below any threshold of quantifiable effects due to forest stand age structure. South. J. Appl. For. 21(1):11-18.

Coexistence of white-footed mice and deer mice may be mediated by fluctuating environmental conditions.

White-footed mice, Peromyscus leucopus noveboracensis, and deer mice, P. maniculatus nubiterrae, occur sympatically throughout much of the Appalachian Mountains of the eastern United States. Previous studies have shown that these two species are behaviorally and ecologically similar and do not partition food or microhabitat. In this paper I use a 14-year data set to demonstrate that the two species have differential population growth and survival rates in response to food abundance and season, which may mediate their coexistence. The ratio of white-footed mice to deer mice ranged from 0.5:1 to 6:1. During summer and times of tood abundance, white-footed mice gained a numerical advantage over deer mice in 10 of 14 years, whereas following winter and poor food production, deer mice had higher survival in 9 of 13 years. The major decline in white-foote mice, but not deer mice, was associated with poor mast (acorn) production in autumn. Differential survival of deer mice may be due to their physiological adaptations to cold temperature and efficient use of torpor during food shortage. Inter-year variance in food production and climatic conditions appear to change the competitive advantage of each species often enough to permit coexistence. Coexistence of these two ecologically similar species may be maintained by different physiological limitations in a fluctuating environment.

Ecology of Lyme Disease: Habitat Associations of Ticks (Ixodes Scapularis) In a Rural Landscape

Human activities often result in the creation of patchy landscapes, which may influence distribution and abundance of some wildlife species and their ectoparasites. Risk of exposure to Lyme disease is a function of the abundance of ticks (Ixodes scapularis, formerly I. dammini), which in turn may be determined by the distribution of key vertebrate hosts within landscapes. We used transect drag sampling and small‐mammal trapping to estimate, respectively, the abundance of host‐seeking and attached ticks in a rural landscape (southeastern New York) consisting of a mosaic of several discrete habitat types. Forested habitat types supported higher densities of host‐seeking ticks than herbaceous or shrub‐dominated habitats. However, in patches of little bluestem grass and gray dogwood shrubs, small mammals had high tick burdens despite low densities of host‐seeking ticks. There was an outbreak of larval ticks limited to oak‐dominated habitats in summer, 1992, which we postulate was related to unusually heavy acorn (mast) production attracting white‐tailed deer and attached adult deer ticks, in autumn 1991. This hypothesis was supported by low densities of larval ticks in oak patches in summer, 1993, following poor mast production the previous autumn. Instead, the 1993 larval peak shifted to maple‐dominated habitats, which may result from intensive use of these patches by deer in nonmast years. The abundance of host‐seeking nymphs was strongly correlated with the abundance of white‐footed mice the prior summer. Both the high tick burdens in little bluestem and dogwood patches, and shifting locations of larval outbreaks, appear to be functions of landscape configuration, especially patch size and juxtaposition.

Diet and condition of wild boar, Sus scrofu scrofu, without supplementary feeding

From 1987 to 1992 diet and condition of two populations of wild boar which received no supplementary feeding were studied in the Veluwe area, a large area of heathlands and forests in The Netherlands, and were compared with those obtained in a previous study (1974–1976), when supplementary food was provided. Composition of stomach contents depended mainly on season, mast availability, and area‐specific factors, whereas sex and age were of little or no importance. Density dependence was found for the decrease in mast (tree seed) consumption from autumn to winter. In autumn, and in winters of rich mast years, mast was the main constituent of the diet. In winters of poor mast years this was replaced by broadleaved grasses in one area and by broadleaved grasses, wavy hairgrass, and roots in the other. We found no important differences between the stomach contents of animals receiving no supplementation, and the natural fraction during a period of supplementary feeding. Variation in body weight was related mainly to age and sex, but also to mast availability. Judged by relative loss of body weight and decrease of bone marrow fat, juveniles seemed to suffer more from poor mast availability than adults. The decrease in body weight from autumn to winter was greater when population density was high. In poor mast years, recruitment into the population receiving no supplementation depended on the availability of broadleaved grasses; in rich years, recruitment was still lower than in populations receiving supplementary feeding. In populations receiving supplementary feeding, recruitment seemed independent of mast availability.

Food caching in the European Nuthatch Sitta europaea

The behaviour and cache sites of European Nuthatches storing naturally occurring beech Fagus sylvatica and hazel Corylus avellana nuts in a South Swedish wood are described. Data are also given on the retrieval of cached nuts in winter and on recaching. On average it took a Nuthatch about 1 min to cache a beech nut. A third of all caches were below 1 m, 20% in the ground. Of those in trees, most were at heights between 5 and 15 m and less than 20% on branches thinner than 4 cm; of caches made above ground, 43% were in dead, often rotten wood. The choice of cache site was related to the kind of item to be cached: a higher proportion of hazel than beech nuts was cached in the ground. Oak was used proportionally more, and other species of tree proportionally less for caching than suggested by their abundance, perhaps because oak presented much dead wood which was extensively used for caching. More than 80% of all caches were covered with material from the immediate surroundings of the cache site. The Nuthatches removed the seed coat from a high proportion of the beech nuts before caching them; however, none of those cached in the ground and similar sites were shelled. During the coldest part of the winter, 1.1 nut per hour was retrieved in a winter following a poor mast crop vs 4.6 in a winter following a rich one. Recaching was common at all times but less so in winter.

How Fox Squirrels Influence the Invasion of Prairies by Nut-Bearing Trees

The purpose of this study was to gain information on how squirrels respond to nuts buried on prairie-forest ecotones as a means of understanding how squirrels influence the invasions of prairies by nut-bearing trees. Of the three common species of nut-bearing riparian forest trees studied, seedlings of black walnut, Juglans nigra , the species whose nuts are most highly preferred by fox squirrels, Sciurus niger , tended to occur farthest from the forest edge onto the prairie. Squirrels removed walnuts buried in the woods in direct proportion to the density of the nuts buried, rather than in proportion to the distance the nuts were located from a conspecific nut-bearing tree. In contrast, when walnuts were experimentally buried at extremely high densities in prairies next to woods during a good mast year, squirrels removed those nuts more quickly that were nearer to the forest and did not remove nuts buried farther than 9 m from the edge of the canopy. Because walnut seedlings were observed at much greater distances from the forest edge, we speculate that squirrels may bury nuts on open prairies at considerable distances from forest cover in poor mast years, when the benefit of fewer nuts lost to other squirrels outweighs the added risk of predation in the prairie.

Environmental Relationships and the Denning Period of Black Bears in Tennessee

The denning period of black bears ( Ursus americanus ) in the Great Smoky Mountains National Park was determined through the use of motion-sensitive transmitter collars. Most (14, 83%) instrumented bears entered dens between 25 December and 7 January. Adult females entered dens first ( X = 31 December), subadults of both sexes entered dens next ( X = 7 January), and adult males entered dens last ( X = 12 January). Emergence generally occurred between 25 March and 7 April, with the denning period averaging 90 days. Females with cubs vacated dens later ( P < 0.002) and denned longer ( P < 0.011) than other adult females. Den entry and strong fidelity to dens by all instrumented bears indicated that the intensity of dormancy did not differ from that in northern regions; however, duration of dormancy was considerably shorter. Cumulative effects of increased precipitation and lower maximum and higher minimum temperatures, which correspond to passage of a low pressure weather front, provided a proximate stimulus to enter dens. Food supply also appeared to affect denning in a proximal manner because bears denned earlier in years with fair to poor mast yields than in years with excellent mast yields ( P < 0.0004). Emergence dates were less strongly correlated with environmental factors. Ultimate synchronization of denning behavior with the environment is best explained by a circannual (endogenous) rhythm; this rhythm is easily shortened or lengthened allowing flexibility depending on environmental variation and the ecology of a species. Such a rhythm encompasses the observed variation in environmental factors affecting the denning period of bears over their broad geographic range and diverse ecological conditions.

Population Ecology of Alberta Red Squirrels

Temporal changes and spatial differences in population structure and density of red squirrels (Tamiasciurus hudsonicus) were investigated in 3 habitats near Rochester, Alberta. Between 1966 and 1969, red squirrels were more abundant in spruce (Picea mariana and Picea alba) stands (161—684/100 ha), less abundant in jack pine (Pinus banksiana) stands (86—264/100 ha), and least abundant in aspen (Populus tremuloides) woods (0—99/100 ha). Summer populations fluctuated between 67 (1966) and 151 (1968) per 100 ha of mixed habitat, but spring populations were more stationary (32—49/100 ha of mixed habitat). Ovulation rates of adult and yearling squirrels and the percentage of yearling ♀ ♀ which bred varied annually. Variation in annual reproductive rate (2.4—4.4 young/♀) was correlated with the date of onset of breeding, and the number of days of snow cover subsequent to 1 January. Juvenile sex ratios were 1:1 but there was a trend toward preponderance of ♂ ♂ in older age classes. Although sex ratios on the study areas were close to 1:1 during early summer, late—summer mortality of adult ♀ ♀ resulted in a preponderance of ♂ ♂ (60%) during the remainder of the year. Equality of sex ratio was restored during the breeding season when ♂ ♂ experienced high mortality rates. After fall dispersal, the percentage of adults was higher in the spruce (78—85%) than in pine (30—50%) but virtually 100% of the squirrels occupying aspen habitat were juveniles. Changes in age ratios suggested that juveniles suffered higher overwinter losses than did adults. Spring age ratios were not related to fall age ratios because of differential annual survival of juvenile squirrels. Dispersal movements occurred in spring and fall; squirrels were relatively sedentary the remainder of the year. The spring shuffle involved breeding ♂ ♂ visiting territories of ♀ ♀ and redistribution of squirrels from deciduous and pine forest into spruce forest. Almost all fall dispersants were young of the year. High adult densities in spruce stands prompted emigration of most juveniles from these areas. Fewer juveniles emigrated from jack pine where adult densities were lower and territories were available. Juveniles apparently dispersed into the large tracts of aspen—dominated deciduous forest. Survival of squirrels varied seasonally and annually, among habitats and between sex and age cohorts. Heavy mortality of adult ♀ ♀ and nestlings occurred between parturition and weaning (July—September). The overwinter period (October—February) was one of high juvenile losses. During the 3—mo breeding season (March—May), ♂ ♂ experienced higher mortality rates than ♀ ♀. Annual survival was highest in the spruce and lowest in the aspen. Survival rates were highest during 1966—1967, °30% lower in 1967—1968, and °44% lower in 1968—1969. Survival of juveniles was lower in all years than survival of adults. In the wild an average of 639 meristematic buds, and the seeds from 35 pine cones were consumed by a single squirrel each day. Captive feeding trials indicated that an average of 176 black spruce cones or 123 white spruce cones per day were necessary to sustain 1 squirrel when offered no supplementary foods. Territorial boundaries in spruce and pine did not change detectably between 1966 and 1969. Within monotypic habitats, territories were similar in size. Territories in white spruce were smallest (x = 0.24 ha), those in mixed spruce larger (x = 0.35 ha), and those in jack pine much larger (x = 0.66 ha). Territory size may be related to cone supply in poor mast years. In 1967, a year of poor cone mast, sufficient numbers of cones were produced per territory to provide one—half of the annual energy requirement of 1 squirrel. The stability of spring populations, despite the change in mast crop from very poor (1966 and 1967) to medium—heavy (1968), implies regulation of squirrel densities at levels which preclude critical food shortage. We hypothesize that territorial behavior is the mechanism which regulates densities about a mean determined by food supply in years of poor cone mast, and that it operates through density—dependent mortality by excluding nonterritorial squirrels from winter cone supplies. Similarities in red squirrel densities (or territory sizes) in similar forest types recorded by numerous authors in different areas and different years imply consistency of territory size within particular habitats. We believe that variation in numbers of squirrels harvested primarily reflects variation in annual production.