Population Ecology and
Current Status

Current distribution and population size

The Scandinavian brown bear is currently distributed across three core areas on the Scandinavian Peninsula (1, 2). The majority of the bear population resides in Sweden with a small portion living in Norway. In Sweden, the core population is found in Dalarna, Jämtland, and Gävleborg Counties, with the rest of the population found in the counties to the north including Norrbotten and Västerbotten (3). In Norway, small pockets of bears persist in the counties Innlandet, Trøndelag, Nordland, Troms, and Finnmark, primarily adjacent to the border of Sweden, Finland and Russia (2). Although the aforementioned regions represent core areas, male bears move across large ranges, particularly during mating season, and can potentially be found anywhere outside the main distribution (4).

The two most recent estimates of the Scandinavian bear population were made for Sweden by the SBBRP in 2017 and then for Sweden and Norway by RovQuant in 2018, with the different methods providing relatively similar estimates (2, 3). Kindberg and Swenson (2018) used the observations from the national DNA monitoring program to calculate the population trend and estimated 2877 (range = 2771-2980) bears resided in Sweden as of 2017 (3). RovQuant used a spatial capture-mark-recapture model to estimate the population of multiple large carnivores in Scandinavia, and reports an estimated 2615 (range = 2499-2732) bears in Sweden and about 140 (range = 124-162) bears in Norway as of 2018 (2). Previous to that, the last population estimates from Sweden were from 2008 (3298 bears) and 2013 (2800 bears) and were also based on the national monitoring scheme (1, 5). Since 2018 the Museum of Natural History (NRM) has been responsible for DNA analyses and population estimates in Sweden Their latest report estimates the number of bears in Sweden to be 2587-3080 in 2022. A study by RovQuant estimated the Norwegian part of the population in 2022 to be between 111-142 (6).  

Population demography

Population demography refers to the study of a population's composition, growth, and structure, including factors such as population size and density, birth and death rates (fecundity and mortality), emigration and immigration rates, age structure, and sex ratio. Understanding the demography of the Scandinavian brown bear population is crucial for management and conservation efforts as it can be used to predict future population trends, assess the impact of management measures, and develop conservation strategies. In Scandinavia, demographic data are collected through national genetic sampling and monitoring efforts, statistics recorded from license bear hunts, and long-term individual monitoring conducted by the SBBRP. Here, we describe what we currently know about the demography of the Scandinavian brown bear population and put it into context.

Population trends and growth rate: During the period of recovery between 1942 and 1991, the bear population increased at a relatively stable rate of about 1.5% per year, meaning the population doubled every 46 years (7). This trend appears to have stabilized and leveled out. The most recent report in 2018 used hunter-collected bear observation data to estimate the bear population trend in Sweden between 1999 and 2017 and suggests that the bear population size in Sweden began to stabilize in the early 2000’s (3). As of now, 2023, high hunting quotas aimed at population reduction will likely decrease population growth rate and the overall size of the population in the coming years. Further research should be dedicated toward monitoring this emergent situation.

The growth rate of any population is influenced by birth and death rates within the population as well as immigration and emigration into and out of the population. A positive growth rate indicates that the population is increasing, while a negative rate suggests a declining population. Bear population growth is regulated by both intrinsic factors (i.e., the behavior of the species and characteristics of the population) and extrinsic factors (i.e., processes external to the population such as habitat and food availability and mortality from outside sources such as hunting) (8). In general, changes in reproductive rates (e.g., the number of females, mean litter size, reproductive intervals, cub survival, and the probability a female will reproduce) have the greatest potential to affect bear population growth rate (9).

However, in Scandinavia, processes external to the population such as hunting play a key role in bear population size and growth, i.e., population growth rates decline sharply when hunting quotas are increased (10) (see the Survival and Mortality section below and Human disturbance and brown bear behavior for more details on the effects of regulated hunting on the Scandinavian bear population). However, there are several bear behavioral characteristics that are likely density dependent (the behaviors shift when bear density increases or decreases) which interlink to have regulatory (intrinsic) effects on bear population growth (8). This includes bear movement and home range size, sex-specific dispersal, social inhibition of breeding, and infanticide (8). Immigration and emigration likely have minimal effect on bear population growth in Scandinavia. The population is generally isolated from the rest of Europe (11), although there is evidence for a higher rate of gene flow from Scandinavia to Karelia (i.e., more emigration) than from Karelia to Scandinavia (i.e., less immigration) at the transborder area where the two populations meet (12). However, considering the level of gene flow, the actual migration rates are estimated to be low (12).

Population density: Population density refers to the number of bears per unit area. The most recent estimates in Scandinavia from 2018 indicated that bear density ranged between 0 and ~7.5 bears per 100 km2 throughout the bear distribution area in Scandinavia, with the highest densities occurring in the southernmost and central core areas (2).

Understanding bear population density in Scandinavia is important as it can affect both population characteristics (e.g., underlying behavior and physiology) and population vital rates (i.e., reproduction and survival) of both the bear population as well as their primary prey populations (e.g., moose and reindeer). Bear density is generally influenced by a mixture of habitat and resource availability combined with human tolerance. As with other species, bear density also affects other aspects of the bear population. For example, variation in the body size of female brown bears is negatively related to bear density, meaning bear body size decreases as bear density increases (13). This is likely due to competition; an increase in population density increases competition for food resources which can result in an overall decrease in body size and weight within the population (13). Such results are to be expected, as density dependent effects on wild animal populations are found throughout the animal kingdom.

Age structure: The ages of hunter-killed bears can be used as a proxy for population age structure which can be broken down into different age classes: cubs-of-the-year (0-1 year old), yearlings (1-2 years old), two-year-olds (2-3 years old), subadults (3-5 years old), and adults (>5 years). In Scandinavia, the mean age of hunter-killed bears (between 1990-2015) was about 5 years old (14).

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The age structure of the brown bear population in Scandinavia is likely heavily influenced by hunting (14), with harvest eventually resulting in a younger population, or an age structure biased toward young animals. There are no observable differences in vulnerability to hunting across different ages in Scandinavia (15). Therefore, in a population that starts off with the majority of individuals in lower age classes, if harvest rates are spread evenly across all age classes, a relatively greater proportion of older aged animals will be harvested, eventually resulting in population that has many more young than old animals. We expect this to be occurring in Scandinavia now, although little is truly known about the age structure of the bear population. This is important because a reduction in the population-wide age of females would have knock on effects on cub reproduction and survival (14, 16, 17). We therefore suggest further research into the age structure of the bear population and its effect on bear behavior and population viability is relevant in the coming years.

Sex ratio: The population estimates suggests that the bear population in Scandinavia is biased towards females; 59% (range = 56%-61%) of the population is female (2). This is likely the result of regulated hunting that protects females with cubs, resulting in female survival being  subsequently higher than male survival (14). Monitoring the sex ratio of the population is essential for understanding reproductive dynamics and genetic diversity.

Reproductive rates: Mean litter size, mean litter interval, and reproductive rates for the Scandinavian bear population were first estimated in 1998; on average, female brown bears in Scandinavia reproduce every 2.4-2.6 years and have an average litter size of 2.3-2.4 cubs (range = 1-4) resulting in a mean reproduction rate (litter size / litter interval) of 0.92-0.96 (18). Litter size was also reported again in 2005, 2012, and 2018 and were generally consistent with previous results; mean litter size was estimated at 2.27-2.37 cubs (19-21). One of those studies also noted that public estimates of bear litter sizes (i.e., reports of cub sightings made by the public) were low and need to be corrected for bias (19), thus the best method for estimating litter size is via continued population monitoring.

Reproductive rates, including the number of cubs born per female, the interval between litters, and cub survival, are critical for assessing the population's growth potential. Importantly, these estimates must be regularly updated as the reproductive rates of a population can change over time based on individual and environmental conditions. Litter size, for example, is related to a variety of factors. A bears first litter tends to be smaller than their subsequent litters (i.e., after the individual has already given birth once before (17), which means a younger population may have overall smaller litter sizes. Litter size is also likely correlated with female body size, meaning larger females tend to have more cubs per litter (22).

Interval between litters is also affected by a number of factors. For example, the probability that one year olds stay with their mother for a second year is greater when the yearlings are small (i.e. have a low body mass) and is more likely to happen when there are two cubs in the litter compared to 3 or 4 (23). The protection of females with cubs during fall hunts results in females keeping their cubs for longer (for 2.5 compared to 1.5 years) which makes the interval between litters longer and can potentially decrease growth rates (10). Infanticide, however, can decrease reproduction intervals; males kill cubs which results in females coming into estrous sooner than they otherwise would have (24, 25). Factors affecting cub survival are discussed in the next sub-section Survival and Mortality.

Survival and mortality: Brown bear survival and mortality rates are influenced by a range of factors in Scandinavia including age, sex, and bear density, but are primarily driven by humans via regulated hunting. Understanding survival and mortality rates is crucial for assessing the health and viability of the bear population.

Age-dependent survival and infanticide: As with most other animals, mortality is highest for bears during their first year of life, i.e., for cubs of the year (26). The majority of mortality occurs during the mating season, most likely resulting from infanticide by male bears (17). In Scandinavia, cub survival varies between regions. For example, a study conducted in 2001 suggests that cub loss is low (~4%) in the northern part of Sweden, but comparatively much higher in the southern population (~34%) (26). This is likely explained by increased infanticide in the south because the male population there has higher turnover rates (i.e., more males die in the south and are then replaced by new males that are more likely to kill local unrelated cubs) (26, 27). One-year olds, or yearlings, have a higher survival rate than cubs of the year, and cubs that stay with their mother longer (i.e., until they are 2 years old) have higher survival rates than those that that leave as yearlings (16). Interestingly, females that settle closer to their mothers home range have a higher lifetime survival (28). For detailed information on infanticide in the Scandinavian bear population see Mating, reproduction, and fitness. Adult females have higher survival rates than adult males as females with cubs are protected during regulated hunts (29).

Natural causes: Like all wild animals, brown bears can die from natural causes including old age, disease, starvation, and injuries from fights with other bears. From 1983 to 2022, only 92 of 560 deaths (16%) of adult marked bears were due to natural causes; 40 were from bears killing other bears and 4 from starvation, and the others were unknown natural deaths (30). The SBBRP has documented only a few cases of adult bears being killed by other bears, and all of these were adult female bears with yearlings; these were possibly the result of females being killed by males during attempted infanticide. Bears in Scandinavia generally do not live long enough to die from old age, and diseases are not prevalent in the population.

Human-related mortality: Humans are the number one cause of death for marked bears in Scandinavia. From 1983 to 2022, 468 of 560 deaths (84%) of marked bears were due to human impact (30). Of the 560, 369 were due to license hunting, 93 due to protection hunts, and 6 due to vehicle and other types of collisions (30). Regulated license hunting in Scandinavia constitutes an additive source of mortality for the bear population, i.e., mortality due to hunting is not compensated by a decrease in mortality from other causes (i.e., compensatory mortality). Bears involved in conflicts with humans, such as semi-domestic or domestic livestock depredation, are also removed via specially permitted protection hunts (31). As one might expect, increased hunting quotas result in a corresponding increase in mortality in the population (9). Hunting quotas and offtake has changed through time in Scandinavia. Illegal poaching also likely occurs within the population with an unknown effect on overall survival and mortality. Finally, vehicle and train collisions can result in bear fatalities, which is more common in the core bear area in southern Sweden that is characterized by extensive road networks and higher bear densities.