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Human influence on the choice of winter dens by European brown bears in Slovenia


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The Slovenian brown bear (Ursus arctos ) population is the only viable population in Central and Western Europe, and it coexists with humans in a multi-use landscape. Bears are most vulnerable to human disturbances during denning. To assess the influence of humans on the choice of winter dens by bears we compared availability and use of caves suitable for denning in central Slovenia. Surprisingly, all direct measures of human influence showed no or only a small effect on the use of the caves by bears. We found that the landscape type (big dolines, canyons, river valleys, and karst plateau) was the most important variable. The less accessible a landscape type is, the more it is used. The probability that a cave in a big doline is used is about 200 times higher than on the karst plateau. Furthermore bears preferred long caves with small entrances away from villages. Bears did not use any cave <540 m distance to the next village. In total, three quarters of all caves were predicted correctly by our model of being used or unused. For conservation and human safety reasons, human activity should be banned from steep ravines and large karst dolines in winter.
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Human influence on the choice of winter dens by European
brown bears in Slovenia
Welf Petram
, Felix Knauer
, Petra Kaczensky
Wildlife Research and Management Unit, Technische UniversitatMunchen, Linderhof 2, D-82488 Ettal, Germany
Alterra Green World Research, Landscape Centre, Team Ecological Modelling and Monitoring, P.O. Box 47, 6700 AA Wageningen, The Netherlands
Institute of Wildlife Biology and Game Management at the Agricultural University of Vienna, Peter Jordan Straße 76, A-1190 Vienna, Austria
International Takhi Group – Research, Salzburg Zoo, A-5081 Anif, Austria
Received 15 February 2003; received in revised form 16 July 2003; accepted 16 July 2003
The Slovenian brown bear (Ursus arctos ) population is the only viable population in Central and Western Europe, and it coexists
with humans in a multi-use landscape. Bears are most vulnerable to human disturbances during denning. To assess the influence of
humans on the choice of winter dens by bears we compared availability and use of caves suitable for denning in central Slovenia.
Surprisingly, all direct measures of human influence showed no or only a small effect on the use of the caves by bears. We found that
the landscape type (big dolines, canyons, river valleys, and karst plateau) was the most important variable. The less accessible a
landscape type is, the more it is used. The probability that a cave in a big doline is used is about 200 times higher than on the karst
plateau. Furthermore bears preferred long caves with small entrances away from villages. Bears did not use any cave <540 m
distance to the next village. In total, three quarters of all caves were predicted correctly by our model of being used or unused. For
conservation and human safety reasons, human activity should be banned from steep ravines and large karst dolines in winter.
Ó2004 Elsevier Ltd. All rights reserved.
Keywords: Brown bear; Human–bear co-existence; Human influence; Denning behaviour; Multi-use landscape
1. Introduction
In Central and Western Europe, brown bears (Ursus
arctos) have been extirpated in most of the areas and the
remaining populations have been reduced to a few small,
isolated and often non-viable populations. Today, only
the bear population of the Alps is slowly expanding, due
to re-introductions and natural dispersal from the large
bear population of the Dinaric Mountains (Fig. 1;
Swenson et al., 2000; Kaczensky and Knauer, 2001),
which is the only natural source for the recovery of the
bears in the Alps. The northern tip of the Dinaric
population is located in Slovenia, where bears and
people coexist in a multi-use landscape.
In the densely settled areas of Central Europe human
activity has become an important factor influencing the
habitat choice of brown bears (Kusak and Huber, 1998;
Kaczensky, 2000b; Knauer, 2000). During the denning
period especially, brown bears are very sensitive to hu-
man disturbance (Swenson et al., 1997; Linnell et al.,
2000) and hence suitable winter dens are an important
component of brown bear habitat. Brown bears use a
wide variety of sites as winter dens depending on abiotic
factors such as climate and geomorphology, and biotic
factors such as sex, age, reproductive status and indi-
vidual preferences (Craighead and Craighead, 1972;
Vroom et al., 1980). Winter dens shelter bears from
unfavourable weather conditions and help to save vital
energy (Folk et al., 1976; Nelson et al., 1983). Even more
importantly, the den provides protection from predation
and human disturbance, especially for reproducing fe-
males (Servheen, 1983; Schoen et al., 1987; MacHutchon
et al., 1993). Surprise encounters by humans with
Corresponding author. Tel.: +31-317-477889; fax: +31-317-424988.
E-mail address: (F. Knauer).
0006-3207/$ - see front matter Ó2004 Elsevier Ltd. All rights reserved.
Biological Conservation 119 (2004) 129–136
denning bears not only disturb them, but may also result
in serious human injury (Kaczensky, 2000a; B. Krze,
personal communication), a major concern in the den-
sely populated bear areas in Europe.
In North America, Tietje and Ruff (1980), Johnson
and Pelton (1981), and Schoen et al. (1987) have shown
that bears choose remote and undisturbed areas for
denning, far from sites of human activity. In most areas
of Europe, human population density in brown bear
range is much higher than in North America (Mattson,
1989). However, bears in Europe have had more time to
adapt to human disturbance and persecution. Several
studies in Europe have tried to assess requirements of
critical denning habitat by describing known winter dens
and by measuring the distances of dens to human in-
frastructure (Huber and Roth, 1997; Groff et al., 1998).
However, describing the choice of winter dens only,
based on the description of used winter dens without
knowing the availability of suitable dens, may cause
biased results.
In Slovenia a high-density brown bear population (1
bear per 10 km2) coexists with people in a multi-use
landscape. Bears seem to tolerate predictable human
activity at close range, at least in summer time (Kac-
zensky, 2000b). Very little data on the location of winter
dens was available, but bears were generally believed to
den only in remote locations. In south central Slovenia,
Podlogar (1997) found that dens were at least 1 km away
from houses, 70 m from roads and 40 m from log-
skidding trails. In southern Slovenia, Potocnik and Kos
(1998) found no den closer than 40 m from a forest road.
But again, no information about the availability of caves
suitable for denning was available.
The objective of this study was to quantify factors
influencing the choice of winter dens by brown bears by
comparing the availability and use of suitable caves in
central Slovenia. Such data would help to identify crit-
ical denning habitat and adapt land use practices in
order to minimise the disturbance of bears and the
chance of surprise encounters of humans with denning
bears. The results would be applied to assess habitat
suitability for brown bear recovery in the eastern Alps
and for feasibility studies in similar areas.
2. Methods
2.1. Study area
The study area comprises 200 km2and is located in
central Slovenia, about 30 km south-west of the capital
Ljubljana. The relief shows typical karst scenery, with
steep canyons, caves and shallow soils. Elevation ranges
from 300 to 1200 m, annual precipitation averages 1500
mm and annual temperature 7–8 °C (Republic of
Slovenia, 1997). In most winters there is a permanent
snow cover for a few months.
The study area can be divided into four major land-
scape types (Fig. 2).
(I) The karst plateau. This covers 73 km2and is strewn
with rocks, small dolines (up to 10 m deep and 50
m in diameter) and caves. Because of the shallow
soil and the irregularity of the terrain the only pos-
sible land-use is forestry. Forest road density is 1.8
km/km2and allows easy access for people. Other
human activities on the karst plateau are hunting
and recreation (biking, hiking, and mushroom
picking). There are no permanent habitations on
the karst plateau.
(II) Seven big dolines, resulting from collapsed large
caves, are situated on the karst plateau. They are
mainly circular, up to 100 m deep, 300 m wide
and with steep rock faces along the walls. Many
caves can be found, mainly from old subterranean
river channels. Because of their inaccessibility
there is hardly any human use despite the fact that
roads are nearby. All these big dolines are situated
on the karst plateau.
(III) There are two canyon systems, the larger one
covering about 24 km2and the smaller one 8
km2. The slopes are steep with multiple rock
faces containing caves. The area is used for for-
estry, hunting and recreation. Parts of the valley
of the bigger canyon are rather densely settled,
Fig. 1. Bear distribution in Europe west of Russia. The shaded areas
show the actual distribution range, the dark dots re-introduced pop-
ulations, and the dotted black line the border of Slovenia.
130 W. Petram et al. / Biological Conservation 119 (2004) 129–136
and the sounds from human activities are audible
in the whole canyon. In the smaller canyon there
are no settlements, but it is frequently used for
recreation, hunting and forestry. Forest road
density is 1.0 km/km2.
(IV) The river valley area is the largest part of the study
area and covers 93 km2. This area is dominated by
rolling hills and small valleys with creeks and small
rivers. Many small villages occur in a mosaic of ag-
ricultural land and forests, dissected by roads.
Caves are only located in the river valleys, which
are characterised by rather gentle slopes with few
rock faces and are more accessible than the can-
yons and are therefore regularly frequented by
hunters, foresters and recreationalists. Forest road
density is about 1.0 km/km2.
Bear habitat consists of mixed, uneven aged forests of
Abieto-Fagetum-Dinaricum, which is dominated by
beech (Fagus sylvatica) and fir (Abies alba), intermingled
with varying amounts of spruce (Picea abies), sycamore
(Acer pseudoplatanus) and elm (Ulmus sp.); forest cov-
erage averages >80%. The forest is intensively managed,
but only selective cutting practices (single tree extrac-
tion) are allowed. Human population density averages
42 inhabitants per km2, but is highly variable within the
study area. Most people live in villages. Single houses
are very rare. Other large and medium sized predators
present in the study area are wolves (Canis lupus),
Eurasian lynx (Lynx lynx), Eurasian wild cat (Felis
sylvestris), red fox (Vulpes vulpes), badger (Meles meles)
and occasionally golden jackal (C. aureus). The ungulate
population consists of red deer (Cervus elaphus), roe
Fig. 2. The four landscape types of the study area and the location of used and suitable but unused caves.
W. Petram et al. / Biological Conservation 119 (2004) 129–136 131
deer (Capreolus capreolus), chamois (Rupicapra rupica-
pra) and wild boar (Sus scrofa).
2.2. Data collection
We conducted all fieldwork between May and Octo-
ber 1998, which is outside the denning period. We sys-
tematically searched for caves in 193 evenly distributed
plots, 250 250 m in size. These plots were located at
the south-western corner of the standard km grid on
1:25,000 topographic maps more or less covering land-
scape types I, III and IV, and together amounted to 12
km2. To increase our sample size, we additionally sear-
ched in all big dolines and tried to search through all
larger rocky outcrops in canyons and river valleys. The
total area searched was about 19.5 km2or 10% of the
whole area.
Use of caves as winter dens by brown bears was
evaluated by the presence of a nest, an excavation and/
or additional indications such as bear scratches and
hairs. Caves without bear signs were classified as unused
caves, but these were classified as suitable if character-
istics were within the range of caves used as winter dens.
We measured a variety of variables on three different
spatial scales to characterise used and unused caves: the
cave itself, immediately around the cave and the general
For the first we noted whether the cave was a natural
cave, a cleft, or a hollow under boulders and the di-
mension of the entrance, tunnel and chamber. We also
assessed the relative humidity of the cave, measured the
dimensions of the (potential) nest, and whether or not
light reached it. The nest could contain vegetation
material such as leaves and roots, but often only a
depression was excavated in the ground.
Around the cave we assessed the visibility and ac-
cessibility of the cave entrance, and mapped the aspect
of the cave entrance as well as the vegetation in a plot
20 20 m around the entrance. The vegetation was
measured as percentage cover of the ground, shrub and
tree layers. We additionally mapped the proportion of
deciduous and coniferous trees.
Finally in an area of 250 250 m around the entrance
we mapped average steepness and aspect of the slope, as
well as the average distance to settlements (more than
five inhabitants), highways, railways, paved roads and
forest roads. In addition we described the vegetation in
the same way as mentioned above.
2.3. Analysis
Before we analysed the factors influencing the choice
of dens, we conducted a threshold analysis in order to
distinguish suitable unused from unsuitable unused
caves. As threshold values we used the minimal width of
the nest found in the 46 used dens, the height from the
middle of the nest to the cave ceiling and the minimum
and maximum volume of the chamber (Table 1).
To find out the most important factors determining
use or non-use of suitable dens by brown bears we used
a multiple logistic regression model (Fahrmeir et al.,
1996). After a pre-selection of the variables from an
ecological point of view we conducted a backward var-
iable selection procedure. Additionally we analysed the
background of the resulting model by bivariate statis-
tics. In multiple comparisons we conducted a Bonfe-
roni–Holm correction (Bonferroni, 1936; Holm, 1977;
Holm, 1979, in Quednau, 1992).
3. Results
Out of 115 caves in total we found 107 suitable caves
of which 46 had been used and 61 had not been used by
bears, but were suitable for denning, according to the
threshold analysis (Table 1).
Of the used caves, 80.5% were natural caves, 17.5%
were clefts and 2% of the winter dens were located under
big boulders. 75.5% of the unused caves were natural
caves, 21.5% clefts and 3% were under boulders. In the
following we call all these structures ‘caves’. There was
no difference between the type of used and unused caves
(v2,n¼107, P¼0:72).
The density of all caves in the four landscapes types
was very different and in decreasing order of frequency
showed the following trend: big dolines (23 caves/
km2)>canyons (7.5 caves/km2)>karst plateau (5 caves/
km2)>river valley area (1.2 caves/km2).
Table 2 gives an overview of the values for the vari-
ables, which we considered to be most important from
ecological reasons. There were no significant differences
between used and unused caves (t-test).
3.1. Variables influencing den choice
Three quarters (75.7%) of all caves were correctly de-
termined by our logistic regression model (Table 3). The
landscape type was the strongest predictor for the use of a
cave. Caves in big dolines had the highest chance of being
used followed by caves in canyons, in the river valleys area
and least likely on the karst plateau. The probability that
Table 1
Ranges for classifying non-used caves as potential dens
Variable Used cave Non-used
Minimum volume of the chamber (m3) 0.50 <0.45
Maximum volume of the chamber (m3) 9.9 >10
Minimum width of nest (cm) 40 <40
Minimum height above the nest (cm) 60 <50
132 W. Petram et al. / Biological Conservation 119 (2004) 129–136
Table 2
Comparison of used and unused caves of all landscape types
Variable Used caves (n¼46) Unused cave (n¼61)
Mean SD Minimum Maximum Mean SD Minimum Maximum
Median entrance height (cm) 59 37 20 255 69 48 24 350
Length of cave (cm) 394 239 100 960 292 173 120 1080
Steepness of slope (°) 37 12 0 58 29 21 0 90
Distance to villages (m) 1818 753 536 3841 1788 1077 273 4411
Distance to forest roads (m) 291 282 32 1029 270 264 5 1082
Table 3
Logistic regression model, calculated with the dependent variable – used caves (n¼46) and non-used caves (n¼61) – and a set of independent
variables characterizing the caves. The band Pvalues for Big dolines, Canyons, and River valley are measured against Karst plateau caves as the
standard. The term ‘diff. )2*log likelihood’ gives an estimate of the relative importance of the four main variables (*, P<¼0:05; **, P<0:01; ***,
Variable bSE exp (b)PDiff. )2log likelihood
Landscape type  36.722
Big dolines 5.3570 1.2051 212.0862 
Canyons 4.6285 1.3363 102.3614 
River valley 4.0827 1.5596 59.3073 
Median height of entrance )0.0281 0.0077 0.9723  18.121
Cave length 0.0054 0.0018 1.0055  12.185
Distance to village 0.0009 0.0004 1.0009 4.520
Constant )5.8166 1.7093 
Table 4
Bivariate comparison of used and non-used caves within landscape types (U-test, P<0:05)
Variable Used caves Non-used caves
Mean SD nMean SD nP
Median entrance height (cm)
Big dolines 72 44 25 96 82 14 >0.1
Canyons 43 14 15 68 34 20
River valley 36 9 3 66 18 7
Karst plateau 58 27 3 54 23 20 >0.1
Length of cave (cm)
Big dolines 335 247 25 292 242 14 >0.1
Canyons 275 176 15 258 124 20 >0.1
River valley 450 223 3 208 58 7 >0.1
Karst plateau 726 135 3 356 173 20
Steepness of slope (°)
Big dolines 38 11 25 43 16 14 >0.1
Canyons 40 8 15 38 17 20 >0.1
River valley 40 10 3 39 5 7 >0.1
Karst plateau 9 9 3 7 10 20 >0.1
Distance to villages (m)
Big dolines 2211 284 25 1693 901 14 >0.1
Canyons 1089 488 15 1172 623 20 >0.1
River valley 900 178 3 822 242 7 >0.1
Karst plateau 3104 657 3 2811 922 20 >0.1
Distance to forest roads (m)
Big dolines 170 96 25 155 74 14 >0.1
Canyons 487 362 15 565 332 20 >0.1
River valley 148 81 3 222 187 7 >0.1
Karst plateau 148 100 3 137 87 20 >0.1
W. Petram et al. / Biological Conservation 119 (2004) 129–136 133
bears use a cave in a big doline was roughly 200 times
higher than on the karst plateau. The second most im-
portant variable predicting cave use was the entrance
height – bears preferred smaller entrances. The third im-
portant variable was cave length – bears preferred longer
caves. The least important, but still significant variable
was the distance to villages – bears preferred caves farther
away from villages.
3.2. Bivariate comparison
In the canyons and the river valley area bears pre-
ferred lower cave entrances, and on the karst plateau
they showed significant preference for longer caves, but
otherwise they showed no such preferences for any cave
types (Table 4). The number of caves close to villages
was too small to make a meaningful statistical com-
parison within or among landscape types. However, no
cave closer than 540 m to any village was used as a
winter den (Fig. 3).
We also found no used cave closer than 50 m to a forest
road, but the sample size of suitable caves was small
(n¼5). Beyond 50 m, forest roads did not seem to have an
influence on the use of caves as winter dens in any of the
landscape types. Humidity and vegetation also showed no
significant differences among and within the different
landscape types and all caves were located in forest. In
general, access to caves in the big dolines and canyons was
more difficult, but within these landscape types, bears also
used caves that were easily accessible.
4. Discussion
We are able to quantitatively determine the influence
of human infrastructure and activity on the choice of
winter dens by brown bears. To our knowledge, this is
the first study of den availability and use by brown
bears. In Slovenia, bears mostly use caves for hiber-
nating. This favoured our approach as the availability is
measurable. According to our radiotracking data (own
unpublished data), bears only use the caves for hiber-
nating, but not as day beds in summer. Otherwise it
would have been difficult to separate the use in summer
from denning in winter by bear signs. We limited our
study area to about the size of the home range of one
male or about three female bears. Because of this we can
assume the same bear density over the whole study area.
In Alaska, Schoen et al. (1987) estimated the avail-
ability of suitable denning habitat from landscape vari-
ables, but without mapping potential dens. For
American black bears (U. americanus), Johnson and
Pelton (1981) also used an availability/use approach,
showing a significant preference of tree dens over
ground dens. Most other studies only described used
dens and tried to draw conclusions on the influence of
human disturbance (Swenson et al., 1997) or human
infrastructure (Huber and Roth, 1997; Groff et al.,
1998). But, because the availability of suitable dens was
not measured, the interpretation of these results is dif-
ficult and the human impact might be overestimated.
Our findings show a quite low impact of human in-
frastructure, but we should point out that most suitable
dens were in steep and rocky areas. We conclude that
bears generally preferred landscape types where the
chances of encounters with humans are lowest. During
the denning period in winter, almost no people enter big
dolines or canyons, hence areas with a lot of caves re-
ceive very little or no disturbance. This means that the
real effect of human influence can be higher, but is in-
cluded in the variable landscape type. If this is so, then
the avoidance of humans acts on a large scale. This is in
accordance with results from North America, where
bears also prefer remote areas (Tietje and Ruff, 1980;
Johnson and Pelton, 1981; Schoen et al., 1987; McLellan
and Shackleton, 1989) and retreat distances are much
larger than in Slovenia.
In accessible areas bears used long caves and/or caves
with small entrances only, whereas in the inaccessible
dolines, far from villages, almost all suitable caves were
used. From this study, we cannot derive predictions
about flat areas without caves or comparable structures.
It might be possible for bears to tolerate a higher rate of
disturbance, but in our study area they had access to
some very secure dens.
In Slovenia, forestry and hunting activities do not
seem to have a negative impact on the brown bear
population. Nevertheless, we know of three cases where
our radio-collared bears were disturbed by humans
while denning (own unpublished data) – two reproduc-
tive females and one subadult male. Whereas the females
did not change dens, the male left but came back after a
week to resume denning. Although the disturbance did
not seem to have caused much harm, data from Sweden
show that the reproductive success of females that are
500 1500 2500 3500 4500
distance in m
not used
Fig. 3. Frequency of caves at different distances from villages. 500 m
seem to be a critical distance to villages. We had a total of nine suitable
caves within this distance to villages in the canyons, dolines and river
valleys, but none of them was used (H0: random, contingency tables,
Fisher test: P¼0:010).
134 W. Petram et al. / Biological Conservation 119 (2004) 129–136
disturbed in a den is significantly lower than that of
undisturbed bears (Swenson et al., 1997). In addition,
there have been several close encounters of people and
bears because people accidentally approached bears in
their winter dens (I. Kos, personal communication, B.
Krze, personal communication, S. Stock, personal
communication). In three such cases the person was
severely injured by the bear.
5. Implications for conservation
Our results can be used to evaluate the suitability of
denning habitat in comparable mountainous and alpine
areas. The following predictions can be derived from
this study:
Bears generally select inaccessible areas that provide a
low potential of human disturbance. Areas that allow
easy access (e.g. flat areas) and receive high human use
are unsuitable. In such areas bears have much higher
safety requirements concerning cave dimensions and
distances to human infrastructure.
In less accessible regions brown bears are less sus-
ceptible to human disturbance and less rigorous in their
den choice. However, to reduce the disturbance poten-
tial for the bears and the risk of surprise encounters
between people and bears, forestry and hunting activi-
ties (especially drive hunts for wild boar) should be
minimised along steep slopes, in big dolines and near
rocky outcrops during the denning period.
For the eastern Alps we predict that, due to the relief,
suitable areas for denning are probably not a limiting
factor. However, in a region with few natural and suitable
caves, bears have to hibernate in open nests or have to
excavate dens themselves. In such a situation, the minimal
distance a bear feels safe from human disturbance might
be longer and any disturbance more critical.
We like to thank Eloy Revilla, Ren
ee de Mutsert, and
an anonymous referee for helpful comments and Wolf-
gang Schr
oder, Klaus Horstmann, Hartmut Gossow and
Blaz Krze for supervising and support in fund raising.
Helmut K
uchenhoff from the Statistical Advice Office at
the University of Munich and his student Thomas Nitter
provided valuable support for the statistical analysis.
Prof. Sustersic of the Geological Institute at the Uni-
versity of Ljubljana, Milan Podlogar of the Slovenian
Forest Service, and Ivan Kos and Hubert Potocnik of the
Biological Institute at the University of Lubljana helped
with their knowledge about bears, winter dens and ge-
ology in Slovenia. Special thanks also to the many people
that helped with the rather demanding field work, espe-
cially: Christine Große, Mateja Blazic, Klemen Sustersic,
Verena Prantner, Evi Tschunko, Falk Petram, Heike
artner, Christian Leidenberger, Ilka Reinhardt,
Marcus Regelmann, Sonja Sinnmayer, Monika Kern,
Daniel Steuer, Philipp Fersterer, Gutrun Batek, Milo
and Knut Renault. Funding for this research was pro-
vided by the Austrian Science Foundation (FWF project:
P 11529-BIO), the Donors Association for the Promo-
tion of Science and Humanities in Germany, and the
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136 W. Petram et al. / Biological Conservation 119 (2004) 129–136
... Past studies have identified a variety of factors responsible for brown bears selecting den sites, including land cover, food resources, topography, and anthropogenic features (Petram et al. 2004;Elfström et al. 2008;Libal et al. 2012;Pigeon et al. 2014). The den site selection process occurs at multiple scales. ...
... Terrain also is a major factor that contributes to the process of den site selection (Petram et al. 2004;Pigeon et al. 2014), with brown bears in some regions selecting only rugged terrain for denning (Whiteman et al. 2017). Past studies found that extreme ruggedness provides brown bears safety from human disturbance, because such terrain is difficult to access during winter months (Nielsen et al. 2004). ...
... To date, most research on brown bear den site selection has been carried out in North America (Ciarniello et al. 2007;Goldstein et al. 2010;Hodder et al. 2014;Pigeon et al. 2014Pigeon et al. , 2016; few studies in Europe have described brown bear dens and the process of den site selection (Huber and Roth 1997;Petram et al. 2004;Elfström et al. 2008). Despite Romania hosting the largest brown bear population in Europe (> 6,000 individuals), excluding European Russia Chapron et al. 2014), denning of brown bear in Romania has received little attention from researchers over the past 50 years (Almășan and Vasiliu 1967). ...
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Dens are important for species that need to survive and reproduce during harsh winters. Brown bears (Ursus arctos) in Romania, listed by the European Union as a population of concern, use dens for several months each year. To date, few quantitative assessments of denning habitat have been carried out for this population or others in Europe. In 2008–2013 and 2015–2017, we used local knowledge and telemetry data from brown bears fitted with GPS collars to identify 115 winter dens and eight open ground nests used by bears in eastern Transylvania, Romania. We located most dens in mountainous areas (64%) and fewer in foothills (36%). Den entrances in mountainous areas were significantly narrower than entrances in foothills, likely due to the need for reduced thermal loss during more severe winters at higher elevations. We selected seven habitat characteristics (abiotic and biotic) and human-related covariates associated with known locations of dens and open nests to identify potential brown bear denning habitat using maximum entropy modeling. We found that terrain ruggedness was the single most important factor when predicting bear denning habitat. The habitat map derived from this study can be used in the future to safeguard bear denning areas from potential human disturbances.
... F = female, Fc = female with cubs, Fp = pregnant female, M = male, S = Subadult, and ND = no age data available. References for the Figure 2: (Clevenger & Purroy, 1988;Craighead & Craighead, 1972;Groff et al., 1998;Huber & Roth, 1997;Judd et al., 1986;Lentfer et al., 1972;McLoughlin, Case, et al., 2002;Petram et al., 2004;Vroom et al., 1980) the availability of food may be the drivers triggering the detected variations in den chronology. However, when taking into account the different classes of bears, that is, adult males, adult females, females with cubs, pregnant females, and subadults, den entry versus latitude was only significant for adult males (n = 12, r = −.58, ...
... Some structural parameters of dens, such as total length, tunnel length, chamber length, and width, may vary considerably (Figure 3), which might be due to the properties of the soil in excavated dens and brown bear adaptability when choosing natural cavities. The small size of the den, compared with that of the bear, allows greater thermal stability, and this is especially notable for excavated dens (Craighead & Craighead, 1972;Petram, Knauer, & Kaczensky, 2004). Some authors have suggested that although the construction of the den is an innate behavior programmed into the bear's genes, it may also be improved through experience acquired from the mother at the yearling stage (Craighead & Craighead, 1972;Petram et al., 2004;Vroom, Herrero, & Ogilvie, 1980). ...
... The small size of the den, compared with that of the bear, allows greater thermal stability, and this is especially notable for excavated dens (Craighead & Craighead, 1972;Petram, Knauer, & Kaczensky, 2004). Some authors have suggested that although the construction of the den is an innate behavior programmed into the bear's genes, it may also be improved through experience acquired from the mother at the yearling stage (Craighead & Craighead, 1972;Petram et al., 2004;Vroom, Herrero, & Ogilvie, 1980). In addition, the features of the caves used by brown bears as dens do not seem the result of population-specific traditions (Chirichella et al., 2019). ...
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• Hibernation represents an adaptation for coping with unfavorable environmental conditions. For brown bears Ursus arctos , hibernation is a critical period as pronounced temporal reductions in several physiological functions occur. • Here, we review the three main aspects of brown bear denning: (1) den chronology, (2) den characteristics, and (3) hibernation physiology in order to identify (a) proximate and ultimate factors of hibernation as well as (b) research gaps and conservation priorities. • Den chronology, which varies by sex and reproductive status, depends on environmental factors, such as snow, temperature, food availability, and den altitude. Significant variation in hibernation across latitudes occurs for both den entry and exit. • The choice of a den and its surroundings may affect individual fitness, for example, loss of offspring and excessive energy consumption. Den selection is the result of broad‐ and fine‐scale habitat selection, mainly linked to den insulation, remoteness, and availability of food in the surroundings of the den location. • Hibernation is a metabolic challenge for the brown bears, in which a series of physiological adaptations in tissues and organs enable survival under nutritional deprivation, maintain high levels of lipids, preserve muscle, and bone and prevent cardiovascular pathologies such as atherosclerosis. It is important to understand: (a) proximate and ultimate factors in denning behavior and the difference between actual drivers of hibernation (i.e., factors to which bears directly respond) and their correlates; (b) how changes in climatic factors might affect the ability of bears to face global climate change and the human‐mediated changes in food availability; (c) hyperphagia (period in which brown bears accumulate fat reserves), predenning and denning periods, including for those populations in which bears do not hibernate every year; and (d) how to approach the study of bear denning merging insights from different perspectives, that is, physiology, ecology, and behavior.
... In connection with the above, much attention is paid to the study of dens and hibernation of brown bears throughout their range in Eurasia and North America. Traditionally, studies are focused on describing the types of dens and their design (Camarra, 1997;Huber & Roth, 1997;Elfström & Swenson, 2009), determining the length of the denning period and factors affecting its timing (Danilov, 1991;Manchi & Swenson, 2005;Krofel et al., 2017), the study of denning site selection by animals (Vroom et al., 1980;Danilov, 1991;Petram et al., 2004), including the effect of anthropogenic factors on the location of dens (Elfström et al., 2008;Elfström & Swenson, 2009). To detect brown bear dens, related timing of den entry and exit, researchers effectively use radio-telemetry (Craighead & Craighead, 1972a;Seryodkin et al., 2003;Elfström et al., 2008;Krofel et al., 2017). ...
... The relative isolation of the den location could be supported by increased requirements for the protective spatial properties of the den in relation to the birth and rearing of offspring. Brown bears most often have dens in hard-to-reach places; this makes them less likely to be disturbed by humans and predators (Petram et al., 2004;Elfström et al., 2008;Seryodkin et al., 2018a). ...
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Space use and the use of a den during the winter period as an adaptation of the brown bear (Ursus arctos) to increase survival during a period of food shortage, are important aspects of the ecology in the practice of the population management. Despite this, the subject of the den locations in relation to space use of brown bears and movements associated with a den entry and exit were practically not considered by researchers. Using radio-telemetry methods between 1993–2012, we studied the space use of 15 brown bears in Sikhote-Alin, three in Kamchatka and two on Sakhalin. The location of 25 dens of tagged animals was determined. The majority of brown bears, mostly males, used space further from the den than from the average of all locations, and the overwhelming majority of dens were outside the core area of their home ranges. So, for brown bears, the spatial location of dens was away from preferred locations in the non-denning period. The same brown bears selected den sites in different denning seasons, both at relatively small distance from each other (1.3 km) and at a considerable distance (20.2 km). Females on Sakhalin moved to dens 7–9 days before the den entry. After leaving their dens, two females in Kamchatka moved 1.7 and 5.0 km on the first day, while on Sakhalin, two females did not move more than 0.1 km from their dens for the first 4 and 10 days. Female that gave birth to cubs in the denning period lingered the longest at the den. The distance of females from their dens and their movement activity decreased in the pre-denning period (10 days before denning, the variations in movement stabilised at a low level) and increased in the post-denning period (specifically after 10 days from the moment of emergence).
... Dens may be dug into the ground, nest dens made of branches on the ground, dens dug under rocks, rock cavity dens (Manchi andSwenson 2005, Elfström andSwenson 2009), root excavation dens, dens in hollow trees, stumps or logs (Vroom et al. 1980, Ugarković et al. 2014. The function of the den is to reduce energy loss and provide safety and protection against disturbance during winter (Petram et al. 2004, Evans et al. 2016. The insulation provided by the den ensures the storage or maintenance of energy (Tietje and Ruff 1980). ...
... Protection and security provided by microhabitat play a key role in offspring survival, minimising energy loss and den selection (Hellgren and Vaughan 1989). Various studies in the Dinaric region have analysed the density of brown bear populations (Jerina et al. 2003(Jerina et al. , 2013, population management (Huber at al. 2008), hunting policies (Knott et al. 2013), impact of human activities on the composition and selection of the den (Petram et al. 2004), the quality of habitat for brown bears (Kusak and Huber 1998) and denning ecology Roth 1997, Ugarković et al. 2014). ...
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The aim of this study was to determine the microhabitat, relief and forest structure characteristics of brown bear (Ursus arctos L.) cave dens and other types of dens in the North Dinarides (Velebit Nature Park) in Croatia. In total, 63 dens were identified, consisting of 89% cave dens and 11% other den types (nest dens 6%, stump dens 3%, trunk dens 2%). In the 20-meter radius around each den, the microhabitat, relief and structural characteristics were recorded, including altitude, slope, exposition, rockiness, forest developmental stage, canopy density, tree height, forest site index, tree basal area, and tree species composition. Based on altitude, the climatic category was determined according to the Köppen climate classification. Most cave dens (62%) were in the temperate climate, at altitudes between 900 and 1,100 m, with a southern exposition and slope class between 30 to 60%. The dens situate in partial canopy density of the third forest site index with tree heights between 16 and 20 m and without forest degradation. Slopes and tree heights were lower (p < 0.019) in cave den areas in comparison to other den types. Keywords: cave dens, microhabitat, forest structure, North Dinarides, Velebit Nature Park
... It has been determined that the bear population density in the Eastern Black Sea Mountains is 194.4 bear/1000 km 2 , one of the highest bear density areas in the world. (Støen et al., 2006) and 100 bears/1000 km 2 in Slovenia (Petram et al., 2004). While only 8-9 bears remain in France, populations in many regions have also disappeared (Swenson et al., 2000). ...
... Although it is mentioned that brown bears choose the easiest routes to save energy [18,66], the local geography of the MNTR is characterized by steep slopes (between 20.3 • and 51.9 • ) with rocky [49] and rugged terrain, not very accessible to humans. This may also be the reason why brown bears, adapted to the local topography, enter the city of Bras , ov, and thus have a clear preference for steeply sloping and undulating, rugged terrain [67], as mentioned in the literature [68][69][70]. On the other hand, considering that most MNTR entry points into Bras , ov city are located on the northern and eastern exposures where biomass production would be higher due to wetter soil and competition for light [71], we can consider that this would facilitate the movement of brown bears up to the border with the urban area, beyond which they would find anthropogenic food sources. ...
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Human–bear conflicts are increasing in number due to deforestation, urban expansion, tourism, and habitat invasion by humans. Our study was conducted in Brașov, a picturesque city in central Romania. Brașov is surrounded by forests and has significant tourist traffic, but also much uncollected garbage and many garbage containers, which attract brown bears. We recorded human–bear conflicts in four districts (Răcădău, the Historic Centre, Noua, and Gară) between 2004 and 2018, finding 55 cases in total, of which in 19 cases involving people, 4 people were killed and 32 were injured. In 36 cases, there were no human victims. We mapped the locations of human–bear conflicts and garbage containers, then analysed their space–time location and human victims in terms of behavioural factors. The altitudes at which brown bears were identified ranged from 580 to 790 m, whereas bears were found in the city at distances of between 100 and 2600 m from the forest. The highest frequency of human–bear conflicts occurred during summer and autumn, and the most common behavioural factor was human outdoor activities. This study provides an important background for understanding human–bear conflicts and will help local authorities develop effective strategies to reduce human–bear conflicts and mitigate risk.
... This is not unexpected given that lynx and other felids are known to use elevated vantage points that provide them with a good overview of the surroundings to easily detect incoming prey or potential danger [52]. Cave entrances are often found in karst depressions [75], which are used by felids for foraging and scent-marking [26]. ...
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Automatic methods for detecting and delineating relief features allow remote and low-cost mapping, which has an outstanding potential for wildlife ecology and similar research. We applied a filled-DEM (digital elevation model) method using LiDAR (Light Detection and Ranging) data to automatically detect dolines and other karst depressions in a rugged terrain of the Dinaric Mountains, Slovenia. Using this approach, we detected 9711 karst depressions in a 137 km2 study area and provided their basic morphometric characteristics, such as perimeter length, area, diameter, depth, and slope. We performed visual validation based on shaded relief, which indicated 83.5% accordance in detecting depressions. Although the method has some drawbacks, it proved suitable for detection, general spatial analysis, and calculation of morphometric characteristics of depressions over a large scale in remote and forested areas. To demonstrate its applicability for wildlife research, we applied it in a preliminary study in combination with GPS-telemetry data to assess the selection of these features by two wild felids, the Eurasian lynx (Lynx lynx) and the European wildcat (Felis silvestris). Both species selected for vicinity of karst depressions, among which they selected for larger karst depressions. Lynx also regularly killed ungulate prey near these features, as we found more than half of lynx prey remains inside or in close vicinity of karst depressions. These results illustrate that karstic features could play an important role in the ecology of wild felids and warrant further research, which could be considerably assisted with the use of remote detection of relief features.
... Female bears may select dens and den sites based on different criteria at different spatial scales (e.g., Petram et al. 2004, Waller et al. 2013, Gray et al. 2016, Pigeon et al. 2016. Thus, to evaluate whether female Andean bears are influenced by characteristics of a cavity independently of characteristics of the site where that cavity was found, we collected and analyzed data separately at both spatial scales. ...
... During the denning period, brown bears generally avoid areas with increased human disturbance, with adult males often choosing den sites in more remote areas than younger bears and females with offspring (Elfström et al. 2008;Elfström & Swenson 2009). Dens are also most often situated in steep terrain with few roads, making them less accessible to people (Petram et al. 2004;Elfström et al. 2008). ...
Bears have fascinated people since ancient times. The relationship between bears and humans dates back thousands of years, during which time we have also competed with bears for shelter and food. In modern times, bears have come under pressure through encroachment on their habitats, climate change, and illegal trade in their body parts, including the Asian bear bile market. The IUCN lists six bears as vulnerable or endangered, and even the least concern species, such as the brown bear, are at risk of extirpation in certain countries. The poaching and international trade of these most threatened populations are prohibited, but still ongoing. Covering all bears species worldwide, this beautifully illustrated volume brings together the contributions of 200 international bear experts on the ecology, conservation status, and management of the Ursidae family. It reveals the fascinating long history of interactions between humans and bears and the threats affecting these charismatic species.
... During the winter denning period, brown bears avoid human disturbance by usually choosing den sites in steep terrain with few roads which are therefore less accessible for people (Petram et al. 2004;Elfström et al. 2008;Sahlén et al. 2011). Adult males often choose den sites in more remote areas, suggesting that the more predation-vulnerable females and subadult males avoid dominant adult males also during denning (Elfström & Swenson 2009;Elfström et al. 2014b). ...
Humans disturb bears in many ways, either directly when they encounter humans or indirectly by changing their behavior and way of life to avoid humans, human activity, and infrastructure. Here we summarize research on how brown bears normally react when encountering humans, what a human encounter may entail for a bear, and whether bears habituate or change their behavior toward humans with increased exposure. Based on this, we also discuss: (a) how our knowledge of brown bear behavior may help people to deal with their fear of bears, and not limit their use of outdoor areas with bears; (b) how human presence, activity, and infrastructure have an indirect effect on bears, that is, how bears change their movement pattern, use of terrain and vegetation, and daily activity pattern to avoid humans; (c) how human disturbance influence foraging and denning, which is crucial for brown bear growth and reproduction; and (d) apparent differences among continents in brown bear behavior toward humans and whether this may have an evolutionary cause.
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In the North Fork of the Flathead River drainage of SE British Columbia and N Montana, reactions of Ursus arctos horribilis were measured primarily by radio telemetry rather than by direct observations to reduce recording biases caused by cover or bear behavior. Bears responded more strongly to ground-based human activities, when in the open than when in cover. Cover had less effect on their response to fixed-wing aircraft. Bears generally displayed stronger reactions to human activities, other than to people on foot, that occurred <76 m than farther away. Strongest response was to people on foot; these reactions were most extreme in areas of low human use. -from Authors
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Winter den abandonment by brown bears Ursus arctos in south-central Sweden and southeastern Norway was found to occur in 9% of 194 bear-winters, based on 68 radio-marked bears almost two years old and older. There was no statistical difference between the sexes, between adults and subadults, nor did protection from military or timber-harvesting activities reduce the rate of abandonment. Although anecdotal, observations suggest that human disturbance was a major cause of den abandonment. Most abandonment occurred early in the denning period, before mid-winter. Bears moved up to 30 km before denning again. Distance was not related to sex, age, or time of abandonment. Apparently for the first time, a fitness cost of den abandonment is documented: pregnant females that changed dens prior to parturition lost young in or near the den significantly more often than those that did not move.
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Denning chronology and behavior of black bears (Ursus americanus) were investigated in east-central Alberta. Twenty-eight instrumented bears were monitored from fall through spring in 1975-76 and 1976-77. Adult males exhibited significantly longer movements to den sites than other cohorts. Bear dens usually were located on the periphery of summer ranges or beyond. Bears selected mixed stands of mature aspen (Populus spp.) and spruce (Picea spp.), or mature spruce stands for den sites. Muskeg was avoided. All but 2 dens were excavated beneath ground level or under rootmasses of fallen trees. All chambers were lined with grasses and litter from the immediate proximity of the den. Observed periods of den construction ranged from 5 to 10 days. Bears entered their dens during a 4-week period starting 7 October in 1975 and during a 5-week period starting 1 October in 1976. Delayed denning in 1975 was attributed to the abundance of blueberries (Vaccinium spp.) that persisted into fall. Denning dates varied among bear cohorts; adult females and subadults denned first and adult males last. The average overwinter weight loss of 11 bears without offspring was 16%. The energy demands of nursing offspring (N = 1 bear) or den abandonment (N = 4 bears) each accounted for an additional 9% overwinter weight loss. Time of emergence from dens spanned the 1st 2 weeks of April in both years. Adult males emerged first and females with cubs last. Females with offspring (i.e., females with cubs or yearlings) remained in the vicinity of dens for an average of 17 days (9-23 days) after emergence, whereas bears without offspring (i.e., adult males, subadults, and barren females) did so for an average of 7 days (2-13 days).
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When exposed to human disturbance, most large carnivores are able to move away from the source with little energetic cost. Bears represent an exception in that during winter, most individuals spend several months in an energy-saving state of hibernation in a den. This implies that disturbance of denning bears has the potential to have a large energetic cost, although data on the subject are rather diffuse. We reviewed the literature on densite selection, denning physiology, and responses to disturbance for the brown bear (Ursus arctos), black bear (U. americanus), and polar bear (U. maritimus). Generally, bears select dens one to 2 km from human activity (roads, habitation, industrial activity) and seemed to tolerate most activities that occurred more than one km from the den. Activity closer than one km and especially within 200 m caused variable responses. Some bears tolerate disturbance even inside the den, but bears will abandon dens in response to activity within this zone, especially early in the denning period. Den abandonment by brown and black bear females with cubs of the year can lead to increased cub mortality. Specific excavated or ground dens are rarely reused, whereas natural caves or hollow trees are reused with varying frequency. There is often some distance between an individual bear's consecutive dens. This indicates that loss of a single denning area following human disturbance will not always lead to deleterious effects, if alternative denning areas are available within the home range.
We studied 21 brown bear (Ursus arctos) dens in the mountains of the northeast Brenta range in Trentino, Italy. Of these, 2 dens were located during the late 1970s using radio-tracking, 1 den was located in 1989 by a different researcher, and 18 dens were located by the authors between 1988 and 1994. Two dens were excavated and 19 were in natural cavities. Bedding material in these dens consisted of nest-like beds (n = 15 dens), a hole dug in the earth (n = 2), bedding materials spread out on the ground (n = 3), and no bed in 1 excavated den. Nine dens showed signs of recent use. To determine factors bears use to select a hibernation site, characteristics (e.g., elevation, exposure, slope angle, and distance from sources of disturbance) were noted for 19 dens located in the area where bears are constantly present and compared with the same character-istics taken from 100 uniformly distributed sites in the same area. Elevation of the den sites ranged between 970-1940 m. The angle of the slopes on which the dens were located ranged between 28°-60°. Brown bears preferred den sites with southern exposure over those with a northern exposure and used slopes facing all cardinal compass directions.
Radiotelemetry data indicated that black bears (Ursus americanus) in the Great Smoky Mountains National Park, Tennessee, prefer tree cavities above ground as winter dens. Adult females and subadults of both sexes selected tree dens more frequently (P < 0.078) than did adult males. Because parturition and lactation occur in winter dens, secluded and well-insulated tree cavities, which provide better protection than ground dens, appear to enhance survival and reproduction. A greater proportion (P < 0.010) of adult females and a higher bear density were found in the primary tree-denning area of the Park. Analysis of vegetation showed no absolute shortage of tree dens; however, their clumped distribution due to logging before the Park was established resulted in tree dens being less available in certain watersheds and especially at low elevations. Site and vegetation differences at dens enabled classification, through discriminant function analysis, of areas with the highest potential availability of dens. Tree dens may afford the extra protection necessary to maintain bear populations within marginal habitats of the southern Appalachian Mountains.
From fall 1981 through fall 1985, 58 radio-collared brown bears (Ursus arctos) were followed to winter dens on Admiralty and Chichagof islands in southeast Alaska. One hundred twenty-one dens were located and their site characteristics described. Mean dates of den entry and emergence, 30 October and 2 May, varied between sexes and among years. Mean elevation and slope of 121 dens were 640 m and 35°, respectively. Dens were at higher elevations and on steeper slopes on Admiralty Island than on Chichagof Island. Females denned on higher and steeper slopes than males. Admiralty Island bears preferred subalpine and alpine/rock habitats and Chichagof Island bears preferred old-growth forest for denning. On Admiralty, rock caves were the most frequent den type; on Chichagof, bears excavated dens most frequently under large-diameter Sitka spruce (Picea sitchensis) or in the bases of large snags. Mine development on Admiralty Island may have caused bears to avoid certain denning areas. Industrial scale logging may reduce brown bear denning habitat in this region. Management recommendations for reducing the impact of human activity and resource development on denning brown bears are provided.