7#>lL,;qHHHHHH)H)H)H)H9 HC HMHMHMHMHM HHmHmHmLHaLLHm@LLLL"L$L(25 November 1992 Djuro Huber Biology Department Veterinary Faculty Heinzelova 55 41000 Zagreb Republic of Croatia (041) 290-141 RH: Bear denning in Croatia: Huber and Roth DENNING OF BROWN BEARS IN CROATIA DJURO HUBER, Biology Department, Veterinary Faculty, Heinzelova 55, 41000 Zagreb, Republic of Croatia HANS U. ROTH, Neumatt 15, 3323 Bariswil, Switzerland Abstract: Twentyeight dens of 15 different European brown bears (Ursus arctos) were located, monitored and measured. Ten of them were used by females with cubs, 9 by females without cubs, 5 by males, and 4 by bears of unknown category. Occasionally bears used more than one den in the same winter, i.e. 4 bears used 2 to 5 dens (mean = 3). Only 2 of this den changes could be explained by human disturbance. The local abundance of natural caves is probably why the most dens (22) were built in rock cavities, 3 were ground nests under the canopy of conifers, 2 were excavated cavities under the roots of large standing trees, and 1 was in a horizontal hollow tree. Int. Conf. Bear. Res. and Manage. 9:000-000 Key words: European brown bear, Ursus arctos, dens, denning, behavior, Croatia. ____________________________________________________________ Brown bears exhibit pronounced seasonality of behavior, mostly imposed by their nutritional and physiological demands. Bears developed a complex strategy to survive the winter period of food shortage: they excessively feed in fall and drastically reduce movements in winter, usually using dens. Also in winter the female gives birth to cubs (1 to 4), which are born very small (<1% of mother's mass) but are fed by very concentrated milk (Jenness et al., 1972) and grow fast enough to be able to follow the mother in spring foraging. The descriptions of dens of European brown bears have sparsely been published in the scientific literature (Roth 1972, Elgmork 1981). The denning of American brown bears and of American black bears (U. americanus) was described for the variety of habitats in North America. We described the dens and their sites of brown bears in Croatia. The denning of known, i. e. radio-marked bears was also analyzed in respect to the sex and age class of the bear. The objective of the study was to determine and describe the important den areas and sites for the proper habitat management practice. The study was supported by the National Geographic Society, the Swiss National Science Foundation, the Croatian Ministry of Science, Risnjak and Plitvice Lakes National Parks, and the Delnice Forest Enterprise. STUDY AREA The studied brown bear dens were located in the section of Dinara Mountains within Croatia: in Lika and Gorski kotar regions with Plitvice Lakes and Risnjak National Parks, respectively, as bear core areas. The elevations range from 417 to 1,528 m above sea level. Depending to the elevation the mean January temperature ranges from -1.2 C in Delnice to -3.6 C on the Risnjak Mountain (Makjani} 1971/72), and the snow cover from 60 to 165 days (Bertovi} and Martinovi} 1981). Forest covers about 70% of the area and this are dominated by a mixture of beech (Fagus sylvatica), fir (Abies alba), spruce (Picea abies) and other tree species varying in composition with elevation and exposure. The topography has typical karst features with various depressions without surface drainage. Limestone bedrock is covered by shallow soils; the mountain peaks and steep slopes (>60 degrees) are formed of bare rocks. METHODS In the period 1981 to 1992 bears were captured with spring activated foot snares, immobilized with ketamine hydrochloride and xylazine hydrochloride, and collared with radio transmitters. The rudimentary first premolar was extracted for age estimation (Stonenberg and Jonkel 1966). Radio locations of marked bears were made by triangulation with hand-held telemetry equipment, by driving forest roads and occasionally by aerial tracking. Visual observations supplemented telemetry data. Inspections and measurements of dens were recorded after bears abandoned them. The found dens of unmarked bears were also measured. Accessible dens were visited in the following years as a check of their reuse. Data were sorted for calculations, and t test was used for comparisons; P>0.05 was considered as statistically significant difference. Measurements of dens in natural rock cavities that differed >2.5 SD from the mean were excluded from calculation. RESULTS Out of 28 dens we found, 22 were slightly modified natural rock cavities, 3 were ground nests under the canopy of conifers, 2 were excavated cavities under the roots of large standing trees, and 1 was in a horizontal hollow tree. We did not record the reuse of any den by radio- marked bears, but 2 of their dens had remains of old nests below the new material. Nine dens were checked for a total of 19 den-years and only one was used again 5 years later by an unknown bear. The examined dens were used by 15 different European brown bears. Ten dens were used by females with cubs, 9 by females without cubs, 5 by males, and 4 by bears of unknown category. Occasionally bears used more than one den in the single winter, i.e. 4 bears used 2 to 5 dens (mean = 3). Only 2 of this den changes could be related with by human (researcher) disturbance. In 2 other cases of our close approaches the den sites were also abandoned but the alternative den was not found or the bear did not den again. The floodings were the likely causes of 2 den abandonages/changes. Den sites were on elevations from 450 to 1370 m (mean = 836 m) with 50% (N = 14) of them from 400-800 m (Figure 1). Den openings were exposed to all sides of the world with no significant preferences (Figure 2). Mean distance from the den to the road accessible by motor vehicles was 486 m (39-1550), and to the nearest house or settlement 1434 m (200-4000) (Figure 3). Fifty percent (N = 14) of dens were distributed evenly in the bear habitat, but the other 50% were found in small concentrations (3-5 dens) on steep rocky slopes in the areas >1 km2. Twenty (71%) dens were in the beach-conifer forest and the remaining 8 in semi-open or shrubby deciduous forest. All but 4 dens were on steep slopes (=>35 degrees), mean = 48 degrees (Figure 4). Three dens were on, or close to, the bottom of small karst valleys and 1 was on a ridge. For the dens in rock cavities the mean slope angle was 53 degrees; 4 of them were above vertical rock walls. Fifteen of 24 (63%) dens on slopes were related to the more or less vertical cliff wall. They were built on the bottom (N = 10) or in a fracture (N = 5) of solid rock. The mean height of rock above dens was 9.4 m (range 3.1-20.0 m), and for the dens in fractures the rock extended downwards for 25.6 m (range 18-34 m). The cavities were the ancient water sinkholes (N = 19) or the space among large boulders (N = 3). Modifications by bear were restricted to the dirt on the cave bottom; enlargement of entrance and/or tunnel and shaping the depression for nest. Fully excavated by bears were only the 2 (7%) dens bellow the roots of large standing trees. Mean measurements of den entrance, tunnel, chamber, porch, slope angle, elevation, and distance to the road/house were calculated for the dens in rock cavities and root excavations (Table 1), and the hypothetical rock cavity den was drawn (Figure 5). There was no significant difference in any dimension of den due to the bear reproductive status or size class; i. e. maternal vs. non maternal (male and female) and bears < vs. >100 kg. Only the nest sizes (Table 2, Figure 5) were significantly (P>0.05) larger (79 by 98 cm) for mothers with cubs and for all bears >100 kg vs. single females and all bears <100 kg (57 by 60 cm). The depths of nests and bedding did not differ. As a bedding material bears used grass, conifer twigs with needles, deciduous twigs, leaves, moss and ferns. However, in 4 dens the bears slept on bare soil with no bedding. In the mean proximity of 16 m (range 2 to 30 m) of 8 dens we found 10 nest-like structures on open ground. Visual conformation showed that one bear, even in the middle of winter (first half of January), and another one in March, used to spend at least part of daytime in this nest, which we called "sun-bed". A family of mother with 2 yearling cubs was seen walking around (up to 150 m) the den site during daytime in the first week of denning in November. Another female that had at least one cub in the den (confirmed by hearing the cubs voice) was repeatedly seen browsing alone around the den until June 04 when the den was abandoned. No den related mortality was revealed in our study. For 6 bears radio monitored over whole winter the mean denning time was 86 days (range 6 to 189 days). The total number of documented bear den-days for 11 bear-winters was of 593. It was distributed as follows: November 4, December 83, January 170, February 170, March 101, April 30, May 31, and June 4 den-days. DISCUSSION Clear preference to rock cavities (79%) as den sites is apparently due to combined effect of the karst environment abundant with appropriate rock formations and to the relatively mild winters. Only Shoen et al. (1987) reported equally high (79%) use of natural cavities for North American brown bears on Admiralty island (Alaska), though on the nearby Chichagof island it was only 11%. Vroom et al. (1977), Pearson (1975), and Servheen and Klaver (1983) reported 0% use of natural cavities, Miller (1990) 1%, Judd et al. (1986) 10%, Van Daele et al. (1990) 13% and Reynolds et al. (1976) 25% in different parts of North America. Most bear dens in Scandinavia are associated with ant-hills and tree stumps (Elgmork 1981). However, for the American black bear in Arizona LeCount (1983) reported 100% use of rock related dens. Van Daele et al. (1990) reported 18% reuse of den by the same bear in the successive years and even 2 cases of females using the same dens in 5 consecutive years. We can not speak about the fidelity of Croatian brown bears to their den sites. Occasional use of the den that was previously used by another bear was reported by Servheen and Klaver (1983) at the level of 13% what is comparable to 8% in this study. Den abandonment was complete (4 cases) whenever our approach made it clear to the bear that his den site is known to humans. We feel that any approach <30 m is likely to chase the bear out of den in any part of the winter. Changes of dens during the winter by European brown bears due to different reasons was reported by Elgmork (1981). Abandonment due to flooding (2 in this study) was also reported by Van Daele et al. (1990) and Shoen et al. (1987) for Kodiak brown bears, and Alt (1984) even noted American black bear cub mortality due to flooding of natal dens. No preference in selection of the exposure of den opening was also reported Van Daele et al (1990), while other authors found preferences to various sides of the world: Vroom et al. (1977) west, Judd et al. (1986) north, and Shoen et al. (1987) south. The mean slope angle (48o overall, or 53o for the rock cavities dens) of den sites is higher than reported in North American studies, i.e. Servheen and Klaver (1983) found 30o, Judd et al. (1986) 20o - 75o, and Shoen et al. (1987) 35o. It could be explained by the availability and as a way for bears to cope with relatively highly man influenced habitat. The bears could be in vicinity to the road or even inhabited houses but on the steep, hardly accessible and seldom by man visited slope. Compared to 14% (4 of 28) of den nests without bedding in this study, Servheen and Klaver (1983) and Judd et al. (1986) found 27% and 24% dens with no bedding, respectively. At least 3 of 4 such nests in this study were in dens only temporarily used and than abandoned or in the emergency constructed dens. While in the den the activity level of bears was around 5% (Roth and Huber 1986). The discovery of "sun" beds and the visual confirmation of their use during winter explains part of this den related activity. Similar structures and bear winter behavior was not found reported for other bears. From telemetry results, from fresh bear scats and tracks in snow found in all winter months, we conclude that many bears in Croatia do not hibernate for the whole winter, and some may even spend the entire winter out of den. Bears exhibited variable dormancy. While each bear showed at least some period of immobility, we could not find the typical wider den for every one. Comparable data were reported by Van Daele et al. (1990) for Kodiak brown bears where 22% did not den. We conclude that in shrinking habitat certain areas will remain as a critical resorts for European brown bear denning and reproduction. We propose their strict protection, i. e. exclusion of all man related activities (constructions, forestry, hunting, sports activities). LITERATURE CITED Alt, G. 1984. Black bear cub mortality due to flooding of natal dens. J. Wildl. Manage. 48:1432-1434. Bertovi}, S., and J. Martinovi}. 1981. Bioekolo{ke zna~ajke. Pages 27-43 in I. Tomac, ed. Gorski kotar. Fond knjige "Gorski kotar", Delnice. Elgmork, K. 1981. Denning behaviour of a female brown bear, Ursus arctos (Linne, 1758), with three young. Saugetierkundliche Mitteilungen. 29:59-66. Jenness, R., A. W. Erickson, and J. J. Craighead. 1972. Some comparative aspects of milk from four species of bears. J. Mammalogy, 53:34-47. Judd, S. L., R. R. Knight, B. M. Blanchard 1986. Denning of grizzly bears in the Yellowstone National Park area. Int. Conf. Bear. Res. and Manage. 6:111-117. LeCount, A. L. 1983. Denning ecology of black bears in central Arizona. Int. Conf. Bear. Res. and Manage. 5:71-78. Makjani}, B. 1971/72. O klimi u`eg podru~ja Plitvi~kih jezera. Geografski glasnik, 33-34:5-24. Miller, S. D. 1990. Denning ecology of brown bears in southcentral Alaska and comparisons with a sympatric black bear population. Int. Conf. Bear. Res. and Manage. 8:279-287. Pearson, A. M. 1975. The northern interior grizzly bear Ursus arctos L. Can. Wildl. Serv. Rep. Ser. 34. 86 pp. Reynolds, H. V., J. A. Curatolo, and R. Quimby 1976. Denning ecology of grizzly bears in northeastern Alaska. Int. Conf. Bear. Res. and Manage. 3:403-409. Roth, H. U. 1972. Standorte von Winterlagern des Braunbaren (Ursus arctos) im Trentino, Italien. Jb. naturh. Mus. Bern. 4:219-230. Roth, H. U., and D. Huber 1986. Diel activity of brown bears in Plitvice Lakes National Park, Yugoslavia. Int. Conf. Bear Res. and Manage. 6:177-181. Servheen, C., and R. Klaver 1983. Grizzly bear dens and denning activity in the Mission and Rattlesnake Mountains, Montana. Int. Conf. Bear. Res. and Manage. 5:201-207. Shoen, W. J., L. R. Beier, J. W. Lentfer, and L. J. Johnson. 1987. Denning ecology of brown bears on Admirality and Chichagof islands. Int. Conf. Bear. Res. and Manage. 7:293--304. Stoneberg, R. P., and C. J. Jonkel. 1966. Age determination of black bears by cementum layers. J. Wildl. Manage. 30:411-414. Van Daele L. J., V. G. Barnes, and R. B. Smith 1990. Denning characteristics of brown bears on Kodiak Island, Alaska. Int. Conf. Bear. Res. and Manage. 8:257-267. Vroom, G. W., S. Herrero, and R. T. Ogilvie. 1977. The ecology of winter den sites of grizzly bears in Banff National Park, Alberta. Int. Conf. Bear. Res. and Manage 4:321-330. 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