TRAFFIC KILLS OF BROWN BEARS IN ,

DJUROHUBER, Biology Department, Veterinary Faculty, Heinzelova 55, 10000 Zagreb,Republic of Croatia,email: [email protected] JOSIP KUSAK,Biology Department, Veterinary Faculty, Heinzelova 55, 10000 Zagreb,Republic of Croatia,email: [email protected] ALOJZIJEFRKOVIC, Croatian Forests, Delnice ForestryOffice, Supilova 32, 51300 Delnice, Republicof Croatia

Abstract: At least 73 Europeanbrown bears (Ursus arctos) have been killed by vehicles in the forest region (1500 km2) of Gorski kotar,Croatia, from 1963 to 1994. Fifty-one (70%) were killed by trains along the Zagreb-Rijekarailway and 22 (30%) were killed by motor vehicles along roadwaysin Gorski kotar. Several parameterswere measuredat known collision sites (n = 46) and at an appropriatenumber of randomsites (n = 61) along roads and railroads. Slope angle and length, as well as longitudinaland perpendicularvisibility at accident and randomsites were not significantly different. We concluded that microsite topographyhad little or no influence on the occurrenceof bear traffic accidents. Instead, food sources relatedto humanactivities, such as garbagealong roads, may have served as local attractantsto bears and were found near at least 15 (33%) accident sites, but at only 5 (8%) of the random sites. We found that 3 main corridorsfor bear movements were cut by traffic lines. Provisionalmitigation measures were proposedto reduce conflict between bears and traffic, and an artificialtunnel or green bridge (100.5 m long) was added to a new highway project.

Ursus 10:167-171

Key words: Croatia,European brown bear, mortality,traffic kills, Ursus arctos.

The brown bear (Ursus arctos) population in Gorski fic or 4.2 bears/year. This alarmingdata prompted us to kotar,Croatia, has grown substantiallyfrom its 1946 low study traffic accidents involving bears. We wanted to to a density of approximately1 bear/10 km2by the early determinewhy some sites had more bear-vehicle acci- 1980s (Frkovic et al. 1987) and seems to be stable since dents thanothers and to proposefeasible mitigationmea- then. Loss of habitatand directhuman-caused mortality sures. Our hypothesis was that the higher local bear may cause the populationto decline in the future. The mortalitywas relatedto: (1) low visibility associatedwith more humansinfluence bear range, the more bear deaths vegetationdensity, slope, and curves on travelroutes, (2) occur from human factors such as shooting, den distur- interruptionof bear travel corridors, (3) various food bance and abandonmentof cubs, nuisance bear control, sources attractingbears to travel routes. and traffic. Roads and railroadscan lead to habitatfrag- We thankto the CroatianMinistry of Science and the mentation and deaths due to collisions with motorized InternationalAssociation for BearResearch and Manage- vehicles. Bears need large ranges because of their feed- ment for financial support.D. Novosel, T. Gomeric, and ing regime, reproductivebehavior, and denning require- G. Gzica assistedin the field work. Special thanksto the ments (Huber and Roth 1993). Bears' opportunistic associateeditor and reviewers for improving our manuscript. food-finding behavior may attract them to discharged humanfoods, carrion,or preferredvegetation frequently located along travel routes. STUDYAREA Ueckermann(1964) published data on traffic kills of The Gorski kotar region (1,500 km2) comprises the 11 mammalianspecies in Germany.Traffic induced bear western edge of occupied bear range in Croatia(Fig. 1). mortalityhas been documentedin Europe(Frkovic et al. The region is mountainous,with elevations rangingfrom 1987 in Croatia,Kaczensky et al. 1996 in Slovenia), but 0 to 1,500 m. Forest covers about 70% of the area, and no analysesof such incidentshave been published.Wood- the main road and railroadrun from the Croatiancapitol, ing and Brady (1987) and Warburtonet al. (1993) re- Zagreb, to the Adriatic seacoast through the middle of ported on American black bears (U. americanus)killed the Gorski kotar area. From 6,600 to 13,100 vehicles/ on roadsin Floridaand North Carolina, respectively (both day use this road. Constructionof a new highway con- USA). nectingZagreb to the AdriaticSea is underwaypresently. Traffic kills of Europeanbrown bears in Croatiacom- prised 11%of total recordedmortality from 1946 to 1985 when 31 (of 281) were killed by traffic in 40 years or METHODS 0.78 bears/year (Frkovic et al. 1987). In recent years Records of traffic-killedbears have been kept by A. (1986-95) traffic induced mortalityrose to 19% of total Frkovic since 1963. The recordsincluded the exact site recordedmortality when 42 (of 217) were killed by traf- and date of collision, sex and age of the bear, and the 168 Ursus 10:1998

Fig. 1. Locationof Croatiain Europeand the Gorskikotar study area in Croatia. type of vehicle involved in each collision. Bears were collision site. Recent collision sites were visited within a classified as subadults(<3 years) and adults (>4 years few days of the accident and the older ones in the same old) by size and appearance,but since 1981 have also season in which the accident happened years before. been aged by counting the cementumlayers on the first Random points were selected at each full kilometer of premolartooth root (Stonebergand Jonkel 1966). road and railroadin the bear range. If a known collision At each known collision site (n = 46) and at 61 random site appearedto be between 2 randomkilometer points, sites along roads and railroadswe measuredseveral pa- the distanceto the closer one was roundedoff to the next rameters:longitudinal and perpendicularvisibility, slope full kilometer. Longitudinalvisibility was determined angle and length, distance to the nearest house, and the based on curves in the roads and railroads,and perpen- length of time that trainsare audiblebefore reachingthe dicularvisibility by vegetationcover andtopography. We BEARTRAFFIC KILLS IN CROATIA * Huber et al. 169 considered the limit of visibility the distance at which 2 occasions, bears were known to have survivedan auto- >90% of a standingperson's body was no longer visible. mobile collision and escaped from the site. The length of a slope was measuredfrom our site to the Means of longitudinal and perpendicular visibility first ridge or valley bottom. Local attractantsfor bears between accident and random sites were not signifi- were defined as (1) any food source related to human cantly different. The slope at the accident sites was activitiesand included garbage along roads and grain spills not significantly steeper than at randomly selected sites from trains, and (2) presence of fruit-bearingvegetation (36? vs. 33?, respectively). Mean lengths of the slope along the road or railroadright-of-way. at accident and random sites were both 51 m. On av- Chi-square(X2) tests were used to comparethe differ- erage, trains at accident sites were not heard until 4 ences between habitatvariables at bear kill and random seconds later than the trains at randomniites(31 vs. 35 sites. Alpha levels were 0.05. seconds, respectively) but this difference was not sig- nificant. Foods that could attractbears were present on at least RESULTS 15 (33%) of the accident sites compared to only 5 (8%) At least 73 bears were killed by trafficin Gorskikotar, of the random sites (P < 0.01, X2 = 8.74). Further- Croatiafrom 1963 to 1994 (Fig. 2). Fifty-one (70%)were more, fresh bear sign (unrelated to the accident) was killed along the Zagreb- railroad,and 22 (30%) found at 4 accident sites, whereas none was found at were killed on roadsin Gorskikotar (Fig. 3). Of all bears the random sites. killed, 26 (36%) were male, 33 (45%) were female, and Bear-vehicle collisions occurred most frequently at 14 (19%) were of unknown sex. Forty-six (63%) bears 6 sections of roads and railroads (Fig. 5). These sec- were subadults (<3 years), 17 (23%) were adults (>4 tions were: (1) Railroad Gomirje- (9 bear years), and 10 (14%) were of unknown age. Collisions collisions), (2) Railroad Vrbovsko-Moravice (7 col- with bears occurredin all months of the year (Fig. 4). In lisions), (3) area from Delnice to Dedin (6 collisions 6 cases, >1 bear died in an incident: 3 cases involved on road, 1 railroad), (4) area of Lokve (road, 2; rail- motherand cub(s) and 3 cases involved 2 cubs each. All road, 4), (5) Railroad Lic-Drivenik (5 collisions), and multipledeaths of bearswere train-relatedaccidents. On (6) Kvarner area (road, 4; railroad, 7).

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Fig. 2. Five-year averages of traffic-caused brown bear mortality in Gorski kotar, Croatia, from 1963 to 1995. 170 Ursus 10:1998

RailroadTracks (N=51) DISCUSSION We concluded that microsite topographyhad little or Unknown no influence on bear traffic accidents. Althoughnot sig- nificant, the for accidents to occur at (19) slight tendency steeper and more forested places reflects areas less suit- able for human settlementsand thereforemore likely to be used as bear travel corridors. Sites of frequentacci- dents indicatedthe existence of 3 bear movement corri- Male(21 dors that have been cut by humantraffic ways (Fig 5). Provisionalmitigation measures have alreadybeen pro- posed to reduce the conflict of bears and traffic on roads Road (N=22) and railroads. For a highway currentlyunder construc- tion throughbear habitatin Gorskikotar, we proposedat least 6 tunnels or viaducts in additionto those planned due to topographicreasons. So far, 1 artificialtunnel or "greenbridge" (100.5 m long) was incorporatedinto the Male(5) highway project. A numberof railroadtunnels should be constructedat critical points. Bearsfeed on varietyof food items (Cicnjaket al. 1987) and are attracted to any abundant or renewable food source. Because 1/3 of the accidentscould be relatedto Fig. 3. Sex distribution of brown bears killed on railroad food attractants,we recommendremoving all human-cre- tracks and roads in Gorski kotar, Croatia. ated bear food sources from along travel ways.

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Fig. 4. Cumulative number of brown bears killed by vehicles by month in Gorski kotar, Croatia,from 1963 to 1995. BEARTRAFFIC KILLS IN CROATIA* Huber et al. 171

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Fig. 5. Mainbrown bear traffic accident points in Gorski kotar, Croatia:(1) RailroadGomirje-Vrbovsko, (2) RailroadVrbovsko- Moravice,(3) area from Delnice to Dedin, (4) area of Lokve, (5) Railroad Lic-Drivenik,and (6) Kvarnerarea. Also indicated are 3 main movement corridors over the main road and railroad through Gorski kotar.

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