Maternal Dens Research Articles

Polar Bear Maternal Den Habitat in the Arctic National Wildlife Refuge, Alaska

Polar bears (Ursus maritimus) give birth during mid-winter in dens of ice and snow. Denning polar bears subjected to human disturbances may abandon dens before their altricial young can survive the rigors of the Arctic winter. Because the Arctic coastal plain of Alaska is an area of high petroleum potential and contains existing and planned oil field developments, the distribution of polar bear dens on the plain is of interest to land managers. Therefore, as part of a study of denning habitats along the entire Arctic coast of Alaska, we examined high-resolution aerial photographs (n = 1655) of the 7994 km2 coastal plain included in the Arctic National Wildlife Refuge (ANWR) and mapped 3621 km of bank habitat suitable for denning by polar bears. Such habitats were distributed uniformly and comprised 0.29% (23.2 km2) of the coastal plain between the Canning River and the Canadian border. Ground-truth sampling suggested that we had correctly identified 91.5% of bank denning habitats on the ANWR coastal plain. Knowledge of the distribution of these habitats will help facilitate informed management of human activities and minimize disruption of polar bears in maternal dens.

Post-Den Emergence Behavior of Polar Bears (<i>Ursus maritimus</i>) in Northern Alaska

We observed polar bear (Ursus maritimus) maternity den sites on Alaska’s North Slope in March 2002 and 2003 in an effort to describe bears’ post-den emergence behavior. During 40 sessions spanning 459 h, we observed 8 adults and 14 dependent cubs outside dens for 37.5 h (8.2% of total observation time). There was no significant difference between den emergence dates in 2002 (mean = 15 Mar ± 4.1 d) and 2003 (mean = 21 Mar ± 2.1 d). Following initial den breakout, polar bears remained at their den sites for 1.5 to 14 days (mean = 8.1 ± 5.1 d). The average length of stay in dens between emergent periods was significantly shorter in 2002 (1.79 h) than in 2003 (4.82 h). While outside, adult bears were inactive 49.5% of the time, whereas cubs were inactive 13.4% of the time. We found no significant relationships between den emergence activity and weather. Adult polar bears at den sites subjected to industrial activity exhibited significantly fewer bouts of vigilance than denned bears in undisturbed areas (t = -5.5164, df = 4, p = 0.00). However, the duration of vigilance behaviors at sites near industrial activity was not significantly shorter than at the other sites studied (t = -1.8902, df = 4, p = 0.07). Results for these bears were within the range of findings in other studies of denned polar bears.

Characterisation of Eurasian lynx Lynx lynx den sites and kitten survival

Abstract We retrospectively investigated characteristics of den structures and den sites used by female Eurasian lynx Lynx lynx in the Jura Mountains and the northwestern Alps of Switzerland. During 1983-2000, we discovered 30 natal and 40 maternal dens belonging to 26 females. Important den structures were closed, i.e. provided good shelter, had few entrances, and measured 1 m2. Dens were found in rocky places, caves and wooden surroundings. Most dens were located in mixed forests with relatively open vegetation allowing for a visibility of 10-20 m. Contrary to our expectations, natal and maternal dens were equally exposed to human disturbance and were found in terrain which could be dangerous for the kittens. Overall, the two den types barely differed. While concealment did not seem to play a very important part at natal dens and while natal dens were almost never open structures, maternal dens were surrounded by a large number of hiding places and the dens and surroundings were rich in visual contrasts...

Influence of Gender and Den Type on Home Range Shape for Striped Skunks, <em>Mephitis mephitis</em>, in Saskatchewan

We investigated gender differences in shape of home ranges for Striped Skunks, Mephitis mephitis, in southcentral Saskatchewan, Canada, during 1993-1994. Data collected on free-ranging Striped Skunks indicated that shape of female home ranges was unaffected by den type (building versus burrow) and was similar to shape of male home ranges. Moreover, type of maternity den did not influence the position of the den within the home range (inside or outside of core area). We conclude that the distribution of Striped Skunks in summer, and the distribution of their foraging activity, are not affected by the availability of anthropogenic den structures.

Landward and eastward shift of Alaskan polar bear denning associated with recent sea ice changes

Polar bears (Ursus maritimus) in the northern Alaska region den in coastal areas and on offshore drifting ice. We evaluated changes in the distribution of polar bear maternal dens between 1985 and 2005, using satellite telemetry. We determined the distribution of maternal dens occupied by 89 satellite collared female polar bears between 137°W and 167°W longitude. The proportion of dens on pack ice declined from 62% in 1985–1994 to 37% in 1998–2004 (P = 0.044) and among pack ice dens fewer occurred in the western Beaufort Sea after 1998. We evaluated whether hunting, attraction to bowhead whale remains, or changes in sea ice could explain changes in den distribution. We concluded that denning distribution changed in response to reductions in stable old ice, increases in unconsolidated ice, and lengthening of the melt season. In consort, these changes have likely reduced the availability and quality of pack ice denning habitat. Further declines in sea ice availability are predicted. Therefore, we expect the proportion of polar bears denning in coastal areas will continue to increase, until such time as the autumn ice retreats far enough from shore that it precludes offshore pregnant females from reaching the Alaska coast in advance of denning.

The effects of forest fires on polar bear maternity denning habitat in western Hudson Bay

The effects of forest fires on polar bear (Ursus maritimus) maternity denning habitat in western Hudson Bay were determined by comparing the physical characteristics of 48 burned and 101 unburned maternity den sites from September 2001 to October 2003. Fire significantly altered vegetation composition and increased the depth of the active layer, resulting in a decrease in the stability of den sites, the collapse of dens, and degradation of the surrounding habitat. Although bears investigated burned areas, analysis of mark and recapture data, satellite telemetry, radio-telemetry, and field observations all demonstrated that bears did not use burned areas for denning. While peat denning habitat is likely not limiting at this time, the re-use and occupancy of peat den sites during the summer may be an important means of energy conservation for pregnant female bears in western Hudson Bay. Increased energy expenditures in association with increased search times for suitable den sites and the excavation of new dens can potentially affect reproductive success. Predicted increases in forest fire activity as a result of climate change, along with the long-term recovery of denning habitat may reduce the amount of suitable denning habitat in the future. Resource managers need to be aware of the possibility of a shift in the distribution of denning bears and further loss of maternity denning habitat in western Hudson Bay.

Recent observations of intraspecific predation and cannibalism among polar bears in the southern Beaufort Sea

Intraspecific killing has been reported among polar bears (Ursus maritimus), brown bears (U. arctos), and black bears (U. americanus). Although cannibalism is one motivation for such killings, the ecological factors mediating such events are poorly understood. Between 24 January and 10 April 2004, we confirmed three in- stances of intraspecific predation and cannibalism in the Beaufort Sea. One of these, the first of this type ever reported for polar bears, was a parturient female killed at her maternal den. The predating bear was hunting in a known maternal denning area and apparently discov- ered the den by scent. A second predation event involved an adult female and cub recently emerged from their den, and the third involved a yearling male. During 24 years of research on polar bears in the southern Beaufort Sea region of northern Alaska and 34 years in northwestern Canada, we have not seen other incidents of polar bears stalking, killing, and eating other polar bears. We hypothesize that nutritional stresses related to the longer ice-free seasons that have occurred in the Beaufort Sea in recent years may have led to the can- nibalism incidents we observed in 2004.

Seasonal, sexual and anatomical variability in the adipose tissue of polar bears (Ursus maritimus)

AbstractWe collected 245 adipose tissue biopsies from adult polar bears Ursus maritimus in north‐eastern Manitoba during the course of long‐term population studies between fall 2001 and spring 2004. In summer, the sea ice of Hudson Bay melts completely and the entire polar bear population is forced to fast on land for c. 4 months. During this period, the adipose tissue of females contained significantly more lipid than that of males, consistent with preparation for pregnancy and lactation. The adipose tissue of females with cubs contained less lipid than that of solitary females, likely reflecting greater mobilization of lipid during lactation. Although most of the population returns to the sea ice to hunt after freeze‐up in mid‐November, pregnant females enter maternity dens where they continue to fast for an additional 4 months. As a result, the adipose tissue of females emerging from dens at the end of this 8‐month ‘reproductive fast’ contained significantly less lipid than females in the fall. There was also evidence of a decline in the adipose tissue lipid content of females emerging from dens over the course of the study. Although this trend was based on limited sample sizes, it suggests that the overall condition of new mothers may be declining. Fat biopsies collected from 20 adult polar bears during a mark–recapture survey on the winter sea ice of south‐eastern Beaufort Sea showed that the fatty acid (FA) composition of the superficial adipose layer was largely uniform with depth; however, lipid content significantly increased from skin to muscle. Finally, adipose tissue collected from the belly, rump and baculum depots of bears killed by native subsistence hunters showed no site‐specific differences in either FA composition or lipid content. These data suggest that a single sample from any large superficial depot will accurately reflect a polar bear's total superficial adipose store. We suggest that lipid content of adipose tissue may provide valuable information on changes in polar bear condition in response to changes in arctic climate and prey distribution.

Home range, denning behaviour and microhabitat use of the carnivorous marsupial Dasyurus maculatus in eastern Australia

AbstractRadio‐tracking of spotted‐tailed quolls Dasyurus maculatus (Marsupialia: Dasyuridae) in the forested ranges of north‐eastern New South Wales revealed that home ranges were extensive, with males occupying large, overlapping ranges [minimum convex polygon (MCP) up to 757 ha] and females occupying smaller, non‐overlapping territories (MCP up to 175 ha). Quolls were partly arboreal, although most activity occurred on the ground or on fallen logs. Hollow logs were most frequently used as dens, but rock crevices, burrows, tree hollows and artificial structures were also used. Individual quolls were located in up to nine different dens and, with the exception of maternal dens, rarely sheltered in the same location on successive days. The large home ranges of the spotted‐tailed quoll and the non‐overlapping nature of female ranges necessitate very large areas of habitat to support viable populations. Fallen timber, used extensively for shelter and in travelling, may serve to enhance the quality of habitat for the species, and should be retained by forest and wildlife managers.

Paternal den attendance is the best predictor of offspring survival in the socially monogamous bat-eared fox

Although considerable data are available on the subject for birds, almost nothing is known about the adaptive nature of paternal care in mammals. I studied the adaptive significance of paternal care in a socially monogamous population of bat-eared foxes, Otocyon megalotis. Between the birth and weaning of cubs males spent significantly more time in the den vicinity than females, and, with the exception of lactation, were involved in all aspects of cub care. Multivariate analyses revealed that, compared to parental size and age, territory quality and maternal den attendance, paternal den attendance was the best predictor of both the number and proportion of cubs surviving to weaning age. I suggest that the parental roles of bat-eared foxes are related to the species' diet, and propose that the beneficial nature of male care may be sufficient to make social monogamy the optimal mating strategy for males as well as females.

Den use by the spotted-tailed quoll Dasyurus maculatus in south-eastern Australia.

Den use was investigated by radio-tracking 28 spotted-tailed quolls (Dasyurus maculatus) at three sites in south-eastern Australia. Dens were recorded in rock crevices, caves and boulder tumbles, hollow logs, tree hollows and windrows and in small wombat (Vombatus ursinus) and rabbit (Oryctolagus cuniculus) burrows. Two D. maculatus were recorded using more than 15 dens during this study. Rock dens appeared to be preferred over hollow log dens. D. maculatus denned alone, except when rearing young and possibly during mating. Females used a number of maternal dens while rearing young, some maternal dens were used in consecutive years.

Bone collecting by hyaenas: a review

Three species of hyaenas are discussed, comparing their scavenging, feeding and hunting habits in relation to bone collecting. Hyaena hyaena and Parahyaena brunnea can be classified as ineffectual hunters but as solitary scavengers, while Crocuta crocuta, although it does scavenge, subsists largely by hunting medium-sized to large ungulates in packs. These differences have given rise to a great deal of conjecture in the past but it is now unequivocally established that the smaller scavenging hyaenas carry food back to their cubs at maternity dens, thereby contributing to extensive bone assemblages at den sites, which, in turn, reflect the faunal assemblage in adjacent areas to the den. Bones such as mandibles and long bones do not disintegrate at the same rate as smaller bones. On the other hand, spotted hyaenas largely feed where they kill their prey on find their food, carrying predominantly long bones away.

Growth and development of Polar bearUrsus maritimuscubs at Denver Zoological Gardens

Since 1994 Denver Zoological Gardens has evaluated the growth and development of 13 captive-born Polar bear Ursus maritimus cubs. In the wild ♀♀ fast while they are in the den; however, at Denver Zoological Gardens food was available all year round and the ♀♀ ate, urinated and defecated in the den, fouling it with a strong ammonia smell. Concerns for the developing cubs meant that the mothers were periodically separated from the cubs in order to clean the den. This provided the opportunity to examine and weigh the cubs until they were 12 weeks old. Additional body-mass data were collected from other zoological institutions either through personal communications or from the literature. Infrared camera, 24 hour videotaping and audio surveillance also provided unique insights into the Polar bear maternity den.

Selection of maternity dens by female polar bears in western Hudson Bay, Canada and the effects of human disturbance

We deployed 19 satellite radio collars on adult female polar bears (Ursus maritimus) in western Hudson Bay to study how pregnant females select maternity-den sites and the degree to which human disturbance might influence this process. To eliminate the possibility that being handled while pregnant might influence the final choice of a suitable site, the collars were attached 1 year before the females were expected to select dens. Our results indicated that pregnant females moved inland and selected an area to den shortly after coming ashore in the summer and remained there if not disturbed. We analyzed 24 years of consecutive data (1979–2002) to examine whether disturbance of pregnant females in the denning area in the autumn affected litter size or mass of cubs the following spring. We defined three levels of disturbance (none—bear not seen; low—bear seen but not handled; high—bear seen and handled), and found that disturbance had no effect on either litter size or the mass of male cubs. However, we did find that females handled in the autumn had significantly lighter female cubs than females that were not seen. Our disturbance of pregnant females occurred in August and September, which is only a few months prior to parturition; it is not known what the effects of disturbance might be in late October or early November, closer to the time when cubs are born.

Detecting Denning Polar Bears with Forward-Looking Infrared (FLIR) Imagery

Polar bears give birth in snow dens in midwinter and remain in dens until early spring. The survival and development of cubs is dependent on a stable environment within the maternal den. To mitigate potential disruption of polar bear denning by existing and proposed petroleum activities, we used forward-looking infrared (FLIR) viewing to try to detect heat rising from dens. We flew transects over dens of radio-collared females with FLIR imager–equipped aircraft, recorded weather conditions at each observation, and noted whether the den was detected. We surveyed 23 dens on 67 occasions (1 to 7 times each). Nine dens were always detected, and 10 dens visited more than once were detected on some flights but not on others. Four dens were never detected (17 percent), but three of those were visited only under marginal conditions. The odds of detecting a den were 4.8 times greater when airborne moisture (snow, blowing snow, fog, etc.) was absent than when it was present, and they increased 3-fold for every 1°C increase in temperature–dew point spread. The estimated probability of detecting dens in sunlight was 0. Data suggested that FLIR surveys conducted during optimal conditions for detection can produce detection rates approaching 90 percent and thus can be an important management and mitigation tool.

Movements of female polar bears ( Ursus maritimus ) in the East Greenland pack ice

The movements of two adult female polar bears (Ursus maritimus) in East Greenland and the Greenland Sea area were studied by use of satellite telemetry between the fall of 1994 and the summer of 1998. One female was tracked for 621 days, the other for 1,415 days. During this time the females used maternity dens on land. If denning periods on land were excluded, the two females used between 73% and 100% of the tracking time offshore where they were able to navigate in the dynamic pack ice and counteract the fast south- ward movement of the ice (up to 30 km/h) in the East Greenland Current. Mean monthly movement rates varied between 0.32 and 0.76 km/h. Both bears had very large home ranges (242,000 and 468,000 km 2 ) within the dynamic pack ice of the Greenland Sea. The facts that the bears made extensive use of the offshore sea ice and that there is a marked reduction of the Greenland Sea ice call for a closer monitoring of the effects of this change on the East Greenland polar bear population.

Behavioral development of a polar bear cub (Ursus maritimus) in captivity

AbstractThe difficulty of observing polar bears (Ursus maritimus) in the wild has prohibited the gathering of behavioral data necessary to develop a baseline set of milestones for monitoring cub development. This study describes and quantifies previously undocumented trends in behavior observed in a captive cub–information that will be useful both in future comparative studies and in the implementation of husbandry improvements. Nearly 400 hr of behavioral data were collected, 100 hr of which were video recordings from the maternity den during the first 3 months of life. Den videos were scored to determine activity budgets and levels of maternal contact. For the remainder of the first year, mother and cub were observed in the outdoor enclosure. The onset and relative frequency of 40 discrete cub behaviors were tracked, as were patterns of mother–cub contact, including nursing and weaning. This study revealed that environmental conditions, habitat enrichment, and conditioning procedures influenced the patterns of developmental behavior exhibited by a polar bear cub. Both climatic and developmental factors had significant effects on the time the bears spent swimming. Management practices, such as environmental enrichment, and a conditioning procedure involving separation of mother and cub caused transient changes in several tracked behaviors. As the cub aged, the longest time between consecutive maternal contacts increased. Nursing bouts recorded per hour of observation decreased, and the duration of individual nursing bouts and pre‐nurse begging periods increased. Zoo Biol 22:507–514, 2003. © 2003 Wiley‐Liss, Inc.

Habitat Characteristics of Polar Bear Terrestrial Maternal Den Sites in Northern Alaska

Polar bears ( Ursus maritimus ) give birth to and nurture their young in dens of ice and snow. During 1999-2001, we measured the structure of 22 dens on the coastal plain of northern Alaska after polar bear families had evacuated their dens in the spring. During the summers of 2001 and 2002, we revisited the sites of 42 maternal and autumn exploratory dens and recorded characteristics of the under-snow habitat. The structure of polar bear snow dens was highly variable. Most were simple chambers with a single entrance/egress tunnel. Others had multiple chambers and additional tunnels. Thickness of snow above and below dens was highly variable, but most dens were overlain by less than 1 m of snow. Dens were located on, or associated with, pronounced landscape features (primarily coastal and river banks, but also a lake shore and an abandoned oil field gravel pad) that are readily distinguished from the surrounding terrain in summer and catch snow in early winter. Although easily identified, den landforms in northern Alaska were more subtle than den habitats in many other parts of the Arctic. The structure of polar bear dens in Alaska was strikingly similar to that of dens elsewhere and has remained largely unchanged in northern Alaska for more than 25 years. Knowledge of den structure and site characteristics will allow resource managers to identify habitats with the greatest probability of holding dens. This information may assist resource managers in preventing negative impacts of mineral exploration and extraction on polar bears.

Chronology of Terrestrial Den Use by Polar Bears in Western Hudson Bay as Indicated by Tree Growth Anomalies

In a large polar bear denning area inland from the coast of western Hudson Bay south of Churchill, Manitoba, previous denning activity was determined by examining tree growth anomalies in the black spruce (Picea mariana) around and above den sites. A concentrated sample of dens was examined at each of three lakes, and 14 additional den sites were sampled individually on nine lakes and streams, for a total of 31 den sites. Trees sampled at these den sites ranged in age from 46 to 236 years (n = 83, mean = 136, SE ± 95.66). Some individual den sites dated back at least 200 years. Although some dens had been used for up to 29 years, most were used for only 12 years or less, presumably until melting permafrost caused their collapse. Half of the dens were reused two years after their initial use, but the probability of den reuse declined in subsequent years to about 0.25 after 10 years. During the 20th century, coincident with a reduction in hunting during 1920-53 and the subsequent abandonment of York Factory, there appears to have been an increase in den activity and an accompanying change in the pattern of denning activity. The rate of disturbance to the trees at dens correlated significantly to the number of polar bear hides traded at York Factory over the 1840-1935 period (r = 0.654; p < 0.005). During 1850-99, denning activity was greater at points more distant from the trading post at York Factory. In 1900-53, there was an overall increase in denning activity, which was greatest in denning areas nearer to York Factory (r = -0.872; p < 0.01). In 1954-93, the increase in denning activity continued, but varied with distance from the coast (r = -0.724; p < 0.05). Mark-recapture studies undertaken from 1970 to 2000 confirm that female polar bears in the western Hudson Bay population have a long-term fidelity to this specific area for maternity denning, and from this study it is evident that the population has used this denning area for several hundred years at least.

Space-use strategies of female polar bears in a dynamic sea ice habitat

In environments with high spatiotemporal variability in resources, animals may exhibit nomadic movements for resource tracking as opposed to long-term area fidelity. Polar bears (Ursus maritimus) inhabit the dynamic sea ice, preying on seals, and demonstrate considerable intraspecific variation in space use. We studied patterns of fidelity and annual range size for 74 adult female polar bears captured in the Norwegian Arctic that were tracked for up to 5 years using satellite telemetry data. We used the autocorrelation structure of movements and distance between observations at a 1-year interval as measures of fidelity. The female polar bears had a circannual migration pattern. Annual range size varied with reproductive state and geographic location of the range. Females entering maternity dens had smaller annual ranges than females not entering dens. Nearshore females had smaller annual ranges than pelagic females, demonstrating different space-use strategies. Repeatability of movement patterns indicated strategy specialization. We suggest that the different space-use strategies result from variation in habitat and prey selection and in sea-ice dynamics. Factors affecting population and predator–prey dynamics may interact differently with the different space-use strategies and yield strategy-dependent outcomes, therefore a knowledge of movement strategies may be important for understanding polar bear population dynamics.