Distribution Of Dens Research Articles

Polar bear dens on the Seal and Caribou Rivers, Manitoba

During aerial surveys, we opportunistically located clusters of polar bear ( Ursus maritimus Phipps, 1774) earth dens on and near the Seal and Caribou Rivers in Northern Manitoba in 2011, 2022, and 2023. Polar bear denning has not been documented in the published literature there before, but there is local knowledge of denning in this area. These dens are of two different types (shallow dens and pits), with similar characteristics to those in the Western Hudson Bay polar bear subpopulation’s main denning area, 120 km farther south. It is not possible to determine whether these findings represent a northward extension of denning by this subpopulation but changes in den distribution, particularly in such previously overlooked areas, need to be monitored and understood to effectively conserve polar bears in a warming climate.

Neo-taphonomy of striped hyena (Hyaena hyaena) in Israel

Humans increase the limited number of daylight hours available to them by using artificial light at night (ALAN) to improve their ability to continue functioning under light conditions. Several studies found that ALAN has multiple impacts on wildlife, and even humans. We examined whether the prey of striped hyenas (Hyaena hyaena), a commensal of human-altered areas, has adapted to this change in the natural environment. We collected prey remains in 12 different dens during 20 breeding attempts between 1993 and 2022. Our analysis shows that ALAN had no impact on diet or den distribution in central Israel. We were able to identify 654 prey items from 49 species in the dens. We divided the species into five main groups: domestic animals (11 species), wild mammals (19), reptiles (3), and birds (17). Domestic animals were the most numerous in the diet. We also found vegetative species, mainly fruits and vegetables, of 10 species in the dens. In conclusion, our study shows that the plasticity of striped hyena feeding behavior, which may vary depending on geographical region and habitat, and is influenced by human and livestock waste disposal. Their respectful behavior and tolerance of human disturbance make the striped hyena an exceptional carnivore, providing ecosystem services. Therefore, public awareness of the importance of protecting this species in the Middle East must be developed to raise appropriate environmental education programs for the public.

Red foxes enhance long‐term tree growth near the Arctic treeline

AbstractRecent climate warming is expected to increase tree growth and productivity, substantially altering ecological function and boundaries in northern ecosystems. Although climate largely determines the range and growth of trees in any biome, variations in microsite conditions can influence growth on a finer scale. Red foxes (Vulpes vulpes) are found in most terrestrial ecosystems and are considered ecosystem engineers through their denning activities. Added soil nutrients from prey remains, feces, and urine could benefit tree growth on dens in subarctic regions by alleviating soil nutrient limitations. We examined growth in white spruce (Picea glauca) trees growing on eight red fox dens and paired control sites at the Arctic treeline. Radial growth was 55% higher for trees on dens than on control sites between 1897 and 2017, despite similarities in tree ages and densities. This enhanced growth was more pronounced in younger trees, consistent with the decrease in growth with age among all trees. By promoting tree growth near the treeline, red foxes may act as hotspots for tree reproduction. Although the impacts on tree growth largely depend on the spatial distribution of dens, predators can create distinct microhabitats across the landscape, leading to increased vegetation productivity, persisting over many decades.

Modeling the spatial and temporal dynamics of land‐based polar bear denning in Alaska

AbstractAlthough polar bears (Ursus maritimus) of the Southern Beaufort Sea (SBS) subpopulation have commonly created maternal dens on sea ice in the past, maternal dens on land have become increasingly prevalent as sea ice declines. This trend creates conditions for increased human–bear interactions associated with local communities and industrial activity. Maternal denning is a vulnerable period in the polar bear life cycle, and den disturbance could lead to den abandonment, cub mortality, and negative population impacts. We used published long‐term data to parameterize a Bayesian hierarchical model of annual land den abundance during 2000–2015, in 4 regions of northern Alaska, USA, with current or potential future oil and gas activity. We also estimated long‐term (1982–2015) shifts in the spatial distribution of land dens within and among regions using kernel density estimation and assessed the influence of local and regional sea ice and snow conditions on den site selection using a random forest resource selection function. Our objectives were to quantify current den distribution and abundance, test for distributional shifts over time, and investigate if those shifts could be attributed to environmental variables related to den habitat. We estimated that between 2000 and 2015, the SBS contained a median 123 dens in a typical year, of which 68 occurred on land. The region between the Colville and Canning rivers, where most current oil and gas activity occurred, also contained the largest fraction of land dens. Overall, land dens were disproportionately concentrated on barrier islands and on land within 30 km of the coast. The probability of dens occurring on land varied from 1982–1999 to 2000–2015 in all regions, and the overall distribution of land dens shifted west between those periods. This regional‐scale change in den distribution was predictable based on spatial and temporal heterogeneity in snow and sea ice conditions within 50 km of individual den locations. Land denning is likely to become increasingly common with continued sea ice loss, and our results and modeling framework could be used to design additional mitigation strategies for reducing the risk of incidental take due to den disturbance.

Evaluating the efficacy of aerial infrared surveys to detect artificial polar bear dens

AbstractThe need to balance economic development with impacts to Arctic wildlife has been a prominent subject since petroleum exploration began on the North Slope of Alaska, USA, in the late 1950s. The North Slope region includes polar bears (Ursus maritimus) of the southern Beaufort Sea subpopulation, which has experienced a long‐term decline in abundance. Pregnant polar bears dig dens in snow drifts during winter and are vulnerable to disturbance, as den abandonment and mortality of neonates may result. Maternal denning coincides with the peak season of petroleum exploration and construction, raising concerns that human activities may disrupt denning. To minimize disturbance of denning polar bears, aerial infrared (AIR) surveys are routinely used to search for dens within planned industry activity areas and that information is used to implement mitigation. Aerial infrared surveys target the heat signature emanating from dens. Despite use by industry for >15 years, the efficacy of AIR and the factors that impact its ability to detect dens remains uncertain. Here, we evaluate AIR using artificial dens and observers naïve to locations to estimate detection probability and its relationship with covariates including weather variables, den characteristics, infrared sensor and altitude, and survey order to identify potential evidence of in‐flight observer learning occurring between surveys. In December 2019 we constructed 14 dens (each with an artificial heat source), and 11 control sites (disturbed sites without dens). Between December 2019 and January 2020, 3 survey crews flew 6 independent AIR surveys within the vicinity of dens and control sites and video‐recorded AIR imagery. Observers identified putative dens either in flight or during post‐flight review of recordings. We assessed detection probability with a simple Bayesian model using 3 subsets of data: 1) all detection/non‐detection data; 2) detection/non‐detection data restricted to instances where sample sites were confirmed to have been properly scanned by AIR during post‐study verification (i.e., when den locations were known); and 3) all dens visible on the recorded imagery during post‐study verification, even if they were not seen during the survey or during post‐flight review. Subsets 1 and 2 most closely resembled den surveys flown for oil and gas industry and had detection probabilities of 0.15 (95% CI = 0.08–0.23) and 0.24 (95% CI = 0.13–0.37), respectively. Detection probability was 0.41 (95% CI = 0.25–0.58) for subset 3. Higher wind speeds and larger den volume negatively influenced detection probability. Our low detection rate compared to previous studies could partially be the result of differences in study design, such as survey flight patterns. Our results suggest that AIR, as it is currently used, is unlikely to detect most polar bear dens in surveyed areas. Resource managers who use AIR should consider a suite of additional methods (e.g., habitat mapping, probabilistic den distribution, AIR methodology improvements) for minimizing impacts of industry on denning polar bears.

Collar temperature sensor data reveal long-term patterns in southern Beaufort Sea polar bear den distribution on pack ice and land

Collar temperature sensor data reveal long-term patterns in southern Beaufort Sea polar bear den distribution on pack ice and land

Scale dependence in occupancy models: implications for estimating bear den distribution and abundance

Monitoring programs are typically designed to identify long‐term trends in animal abundance, however estimating abundance at a relevant scale can be logistically prohibitive. This is particularly true for species that occur at low densities or those with large home ranges. In such cases, occupancy surveys are often employed in place of more expensive abundance estimation techniques such as mark‐recapture because precise estimation of occupancy probability generally requires fewer data. Although choice of plot size is a critical design element of occupancy monitoring, relatively little effort has been expended to develop or test plot size recommendations. Animal movement between surveys can complicate efforts to obtain an optimal plot size, but surveys of fixed objects, such as nests, dens, or burrows can provide insight about scale effects because the population exposed to sampling does not change during the duration of the survey. We used repeated aerial occupancy surveys to obtain estimates of brown bear (Ursus arctos) den distribution and abundance in a portion of Katmai National Park and Preserve in Alaska. We then used these data to assess the importance of plot size selection and highlight the effects of spatial grain on the resulting inference and utility for monitoring. Scale effects in estimates of mean den‐based site occupancy, but not total den abundance demonstrated that careful selection of sample unit size is important if estimating occupancy probability is a primary monitoring objective. We expect occupancy surveys based on important structures such as nests or dens could have wide applicability for many species.

Dwellers in dens on sandy bottoms: Ecological and behavioural traits of <em>Octopus vulgaris</em>

Four visual censuses targeting Octopus vulgaris living in dens on sandy bottoms were carried out from June to October 2013 in the National Park of the Atlantic Galician Islands (NW Spain). Censuses were undertaken by scuba diving between 5 and 21 m depth in daytime. The total area swept was 13.75 ha. There were no significant differences between octopus presence in dens during open and closed fishing seasons. Depth had a significant negative relationship with occupancy. The average number of dens per 1000 m 2 was 3.84±0.84 in June and 3.89 in October. The area per den was 260 m 2 . Den number estimations varied between 1586 and 2057. The largest number of dens (76.5%) was found between 5 and 10 m depth. Den distribution was clumped. No significant differences were found between octopus size classes (small, medium and large) and den diameter. Associate dens were observed. There were no significant differences in den diameter and shell types found around the middens. Many dens could be “permanent”. Drilling bivalve shell behaviour is discussed. The surveyed area had around 1100 individuals, mainly small specimens. No significant differences were found between octopus size and depth. Substrate, den type and food abundance and availability (especially razors Ensis arcuatus ) seem to be the main factors influencing dens and octopus density and distribution. Den availability does not appear to be a limiting factor in this case. Temperature, den availability, predators and fishing pressure influencing density and distribution are discussed. Rodas inlet may be a preferential habitat for O. vulgaris individuals ranging from 200 to 2000 g, but especially small specimens ( ≤ 1000 g).

A predictive spatial model for gray wolf (Canis lupus) denning sites in a human‐dominated landscape in western Iran

AbstractPredictive models of species denning habitat are useful for understanding distribution of core use areas and identifying areas with potential conflicts. Wolf den site selection in unmanaged areas with dominance of agriculture‐lands and human disturbance is not completely understood. We used a GIS multivariate model based on the Mahalanobis distance statistic and 11 digital habitat layers to evaluate gray wolf denning site suitability in Hamedan province (HP), western Iran. Results showed that >74 % of dens occurred in potential denning sites that occupied 14 % (2,785 km2) of the study area. Based on sensitivity analysis with ROC, we found that the distance to rangelands, elevation, and distance to roads, human settlements and streams were the most predictive variables. Our potential distribution model of wolf den sites showed a very good overall performance according to classification accuracy and discrimination capacity. Denning in elevated rugged terrains adjacent to rangelands and away from roads and villages revealed that wolf den distribution in HP is highly influenced primarily by factors associated with human disturbance. The derived predicted distribution map can be used to prioritize areas for conservation, identify areas with potential conflicts, and to implement adaptive management in regions beyond wilderness and protected areas.

Polar bear (Ursus maritimus) maternity den distribution in Svalbard, Norway

The aim of the current study was to identify maternity denning areas and to describe aspects of denning behaviour in polar bears (Ursus maritimus) in Svalbard, Norway. Den observations made during aerial and ground surveys (n = 553), observations of recently emerged family groups made during capture and tagging of bears (n = 206), and dens recorded by satellite telemetry (n = 76 dens) were used to describe the distribution of dens in the Barents Sea region. Data were collected during March, April, and May from 1972 to 2010, and while most dens were abandoned during the first 2 weeks of April, there was substantial variation. The highest number of dens was recorded on the islands in the eastern and northern parts of Svalbard with fewer dens found further west on the island Spitsbergen. Females with cubs-of-the-year or their tracks indicated some denning in southern, eastern, and northern parts of Spitsbergen. Telemetry also revealed that females captured in Svalbard and the Barents Sea den in Franz Josef Land, Russia. The majority of dens (62%) in Svalbard were located on land within ca. 1 km of the shore with the most inland den 19 km from shore. Heavy exploitation of polar bears before 1973, when a hunting moratorium was implemented, likely led to reduced denning in some areas. Our observations of den distribution indicate that denning is now more widespread in the archipelago than 50 years ago and reflects a reestablishment of denning areas following years of protection.

Opium in the City

The article examines the insertion of opium houses at different levels of the urban space of Guangzhou—from the largest to the smallest: the areas of Honam and Hopei, the districts, the streets—during the years 1923 to 1936. The distribution of dens changed mainly due to shifts in the strategy of the authorities, who paid special attention to the visibility of opium houses in the city and to the reactions of den operators concerned with the viability of their establishments. However, the distribution of dens remained the same throughout the period: an exceptional concentration of opium houses in Henan (Honam), the part of the city located south of the Pearl River. There were three different types of opium houses: sordid dens selling cheap adulterated opium, middle-range “local opium houses,” and high-class opium houses. Each type had a specific distribution throughout the city’s space corresponding to the nature of its consumers’ demands.

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.

Use of rockshelters by carnivores in the Puna. Implications for hunter-gatherer archaeology

This paper deals with mammalian carnivore dens in rockshelters in the Puna of Andean South America. This is analysed in relation to the potential overlap of interest in topographic resources with human predators and the use of these refuges by both agents. Different Puna areas have been surveyed, and eighteen modern taphonomic sites have been studied in the light of local carnivore ecology. Here the results concerning the use of space by carnivores are presented, together with predictions regarding the differential distribution of the taphonomic processes they generate. The aim is to assess which archaeological sites are most prone to have been affected by these processes.Once proximity to critical resources is satisfied – especially water and predictable sources of hunting and scavenging represented by human residences – den distribution seems to be a function, at least partially, of rockshelter availability. Where rockshelters abound, more archaeological sites in these loci can be expected to have been ...

Translocation of an imperilled woodrat population: integrating spatial and habitat patterns

AbstractMany species have strong habitat preferences that directly influence population viability. For successful reintroduction of threatened populations that rely on habitat structures, the correct placement of artificial structures is also important to population persistence. In this paper, we present a hierarchical approach to the problem of translocating animals that rely on permanent habitat structures, in which we first use population dynamics data to identify areas of suitable habitat, and then identify optimal configuration for habitat structures. We use data collected from a non‐endangered, conspecific population of the endangered riparian woodrat (Neotoma fuscipes riparia) to examine the degree to which the distribution of dens in translocation sites might influence the likelihood that animals persist in their new environment. We characterize the habitats in which dens occur, analyze their spatial clustering, and compare them to temporal changes in population status for sex and age classes. We compare the potential efficacy of translocation efforts using spatial analysis versus solely habitat‐based approaches and identify the optimal spatial configuration of dens that should be considered in this translocation effort. We found that patterns of habitat use were positively correlated with overstorey cover, and animal weight was positively correlated with understorey cover. Woodrats appear to select den locations on the basis of understorey cover, but also benefit from dense overstorey cover and distance to nearest tree. Our results suggest that in translocation efforts, artificial dens should be placed in clusters within a radius of 15 m, as values above and below this value showed negative correlations with body mass. Translocations should occur after reproductive events, which occur in April and August for woodrats in southern California. Our analyses provide practical guidelines in determining appropriate timing and spacing for translocation events in the context of animal condition, minimizing disease transmission, and reproduction.

Characteristics of current and historical kit fox (Vulpes macrotis) dens in the Great Basin Desert

We examined the ecological and physical characteristics of den sites for 13 adult kit fox (Vulpes macrotis) in western Utah from December 1998 to February 2001. We also compared current and historical den distribution among habitat types. The number of den sites used was not influenced by home-range size (P = 0.11) or season (P = 0.40), but was influenced by geographical area. Home-range size was smallest (P = 0.007) and the number of dens used was greatest (P = 0.009) in mountainous areas. Ecological and physical characteristics of single-use dens (n = 30) were compared with those of multiple-use (n = 53) and natal dens (n = 8). Characteristics that differed between den types included number of entrances (P = 0.0001), diameter of entrances (P = 0.003), and height of vegetation along transects (P = 0.0001). Natal den entrance azimuths were weighted towards a northwesterly aspect (P = 0.0022); however, single- and multiple-use den exits appeared to be randomly distributed. Historical changes in kit fox den site selection have occurred since 1959 (P < 0.0001). We characterized more dens in invasive grasslands and fewer in greasewood (Sarcobatus vermiculatus) habitats than previously described. The conversion of native habitat to grassland and the increase in coyote population may have altered kit fox distribution to include mountainous areas not previously described.

Human Disturbances of Denning Polar Bears in Alaska

Polar bears ( Ursus maritimus ) give birth in dens of snow and ice. The altricial neonates cannot leave the den for >2 months post-partum and are potentially vulnerable to disturbances near dens. The coastal plain (1002) area of Alaska's Arctic National Wildlife Refuge (ANWR) lies in a region of known polar bear denning and also may contain >9 billion barrels of recoverable oil. Polar bears in dens could be affected in many ways by hydrocarbon development, but neither the distribution of dens nor the sensitivity of bears in dens has been known. I documented the distribution of dens on ANWR between 1981 and 1992 and observed responses of bears in dens to various anthropogenic disturbances. Of 44 dens located by radiotelemetry on the mainland coast of Alaska and Canada, 20 (45%) were on ANWR and 15 (34%) were within the 1002 area. Thus, development of ANWR will increase the potential that denning polar bears are disturbed by human activities. However, perturbations resulting from capture, marking, and radiotracking maternal bears did not affect litter sizes or stature of cubs produced. Likewise, 10 of 12 denned polar bears tolerated exposure to exceptional levels of activity. This tolerance and the fact that investment in the denning effort increases through the winter indicated that spatial and temporal restrictions on developments could prevent the potential for many disruptions of denned bears from being realized. Key words: Alaska, ANWR, Arctic, denning, disturbance, impact, oil development, polar bear, reproduction, Ursus maritimus

Distribution of wolf dens on migratory caribou ranges in the Northwest Territories, Canada

Most wolves (Canis lupus) on migratory caribou (Rangifer tarandus) ranges in the Northwest Territories den near the tree line, the northern limit of tree growth. Sixty percent of the 209 dens that we located were within 50 km of the tree line, an area representing only 25% of the caribou range. Den density in the forest was significantly lower than expected if dens were randomly dispersed. Within the tundra zone wolves did not show any preference for denning near caribou calving grounds. Most wolves may den at the tree line because caribou are likely available for a greater proportion of the denning period than they would be elsewhere and because caribou are usually abundant near the tree line in September, when the nutritional demands of the pups are greatest. Within the tree-line zone, habitat characteristics appeared to affect the local distribution of dens because wolves preferred to den where the roots of trees and shrubs provided structural support for the tunnels. With most wolves denning at the tree line, density-dependent summer range expansion and contraction by caribou may provide a mechanism by which changing caribou densities could influence the growth rate of the wolf population.

Den distribution and den use by the red fox Vulpes vulpes japonica in Kyushu

AbstractThe distribution of dens and den use by the red fox was studied in Kumamoto Prefecture between 1968 and 1982. A total of 80 dens were classified into natal, residential, and temporarily‐visited dens. Natal dens comprised 12.4% of all dens. Relative proportions were quite stable for a long period. This indicates a constant number of reproducing females in the area for a considerable length of time. Seasonally the utilization of den showed three peaks in February, May and October. The peaks coincided well with the peaks of reproductive activity of female foxes. The results of multiple regression analysis of distribution of dens with respect to selected environmental parameters around densites indicated that the fox selectively utilize open land, rather than densely vegetated areas. The persistence of dens, the selective utilization by foxes of open land and the sizes of dens were all related to the breeding activities of female foxes inhabiting the area. Reproductive females usually used plural dens (“den group”) in one reproductive season. The numbers of those females occuring in the area were maintained at a steady level for fairy long periods. These indicate that the existence of a stable social relationship between females mediated through occupancy of “den groups.”