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               GPS-GSM collars send position data of a brown bears
             in Croatia via mobile phone system

last update: July 13, 2005

Department of Biology at the Veterinary faculty
of the University of Zagreb, Croatia

by Ðuro Huber

NEW Bear Marko 2005

The male bear “Mladen” under drugs at September 2003

GPS GSM collar on a bear in Croatia. The first GPS-GSM collar send GPS data in a bear research project via mobile phone system (GSM). The GPS-GSM collar was fitted on a young male bear in September 2003. The GPS collar takes locations all hour.

On 25 September 2003 the first brown bear in Croatia has been marked with a GPS-GSM collar that records the bear’s movements with the Global Positioning System (GPS) and sends the locations over the mobile phones network (Global System for Mobile Communication = GSM) as an SMS messages directly to our office. Each SMS contains seven GPS fixes and additional information. In the case of no network coverage the GPS-GSM collar will retransmit the stored SMS next time when GSM coverage is available. This is the most secure option to get maximum data  and the cheapest way of data transmission.

Fig. 1: The red area shows the location of Croatia

The GPS-GSM collar is supplied with a VHF beacon which makes possible to use terrestrial telemetry equipment to locate the bear. Over that activity-, temperature- and mortality sensors are integrated into the collar to uptake multiple data.-

The collared bear is male with 109 kg mass and 4 years old (figure 2). His name is “Mladen.
The locations are immediately mapped and updated on this web site every two weeks.

Fig. 2: Ðuro Huber just fitted the GPS-GSM collar on the 4 year old male bear “Mladen”










The goal of the study is to document the continous movements of a bear by GPS-GSM collar in relation to the new constructed highways in Croatia. The highways have a number of tunnels and viaducts. In addition 3 green bridges, 100 – 120 m wide, have already been constructed (figure 3). We want to see if the bear is crossing the highway and where he does.


Fig. 3: Green bridge under construction and in operation

Unrestricted movements are crucial for the survival of populations of large carnivores such as bears. They need a vast space to fulfill all their biological requirements: finding food, shelter, a sexual partner, a dening site for winter sleep, and to avoid trouble with other bears and, above all, with people.

About 400 to 600 bears are living in Croatia. They are game species hunted under yearly quota regime. The information about their spatial needs and movements can help to manage the population in the way that will secure their long term survival. We hope to follow the bear continously via the GPS-GSM collar.

Fig. 4: Movements of “Mladen”, September 26- December 22, 2003

The capture site was selected to be close (1.5 km) to the highway connecting Zagreb and Rijeka at the seaside of Croatia. The bear moved straight away from the highway for about 10 km and is now using the large area shown on the map. This is the mountainous and forested part of the country with no human settlements and no major traffic routes. Without this especial location data transmission of the GPS-GSM collar carried by bear Mladen his movements would remain largely unrecorded if only the traditional VHF radio telemetry is available.

Fig. 5: Detailed movements of “Mladen”, September 26, 2003 - May 6, 2004

Since the capture and marking in late September the bear Mladen is using an area of roughly 100 km2. We are not tracking the bear long enough to allow us to call this area as his home range. The most distant point from the capture site was 19 km. Mladen is showing a fall activity center or "core area" of some 30 km2. He made four "excursions" from this core area, each 6 to 9 km in linear distance. The very capture site was one such excursion.

The concentration of activities to certain areas in fall can be explained as optimised strategy for food foraging. In the period from September to December the bear has to accumulate enough body fat to make through the winter. One of the mayor fall food sources are beech nuts found on the mountain slopes with mature beech forests.

Although bears do not defend their territory against other bears, even the young adult male like Mladen likes to stay away from other dominant males. Probably he found his peaceful patch where the most of locations are concentrated. We expect Mladen to settle down when the first mayor snow comes. There was about 15 cm of snow around 20 December but it mostly melted already. In the case that the winter passes with little or no snow, a young male bear like Mladen may keep to be active all winter long. If he makes a den it will likely be outside of the core area he is using now. The mayor moves we expect next spring when the mating season starts in May. Maybe he will the have to cross one of the highways as we expected from the beginning.

Mladen spent over three months in the den at the very rugged and remote location with no GSM coverage. During that time we tracked the bear by VHF signal. The collar on Mladen had a "home made" drop off system of wires that rust with time. The plan was that they will hold about 1.5 years but they broke after 6 months. The bear denned at a wet spot and the oxidation was fast. All stored GPS locations, activity- and temperature data are outried from the collar. The activity and ambient temperaturof the bear has been monitored by a two axis activity logger (fig. 6). By this, the acceleration of the collar will be estimated 6-8 times every second and the overall mean value has been stored every 5 minutes.

Fig. 6: Activity data of Mladen in x- and y direction (blue and green symbols) and temperature data (red line),  September 2003 to May 2004


A new project has been started: On 10 September we captured the second bear to carry the GPS/GSM collar, we named him Marko. The capture site was only 2 km far from the one where we collared Mladen. The new bear is also male, 141 kg, probably 5.5 years old. In 2003 the bear Mladen lived a couple of km south of highway (figure 4) and never crossed it. The bear Marko demonstrated different behaviour.


Fig. 7: Detailed movements of bear “Marko”, September 10, 2005 - July 13, 2005 (n=1966)

After about two weeks of slow moves in the direction north he crossed the highway on the most exciting spot for us as researchers and conservationists. He used the specifically built wildlife crossing, the green bridge called Dedin north of the town Delnice on early morning of 29 September between 05 and 05 hours. He also crossed the railroad and the old highway. The bear continued to move north and crossed the railroad and the old highway again and now is east of the town Skrad, 20 km from the capture site. In this area he might be finding plenty of various fruits in remote and abandoned orchards. He has to accumulate a lot of fat tissue for winter denning. Marko is in the den since 27 December, close to where we collared him (figure 7). This site is not far from where the other bear Mladen had his den the previous winter.

Marko left the den on 13 March 2005. We found the den in April exactly where the GPS location directed us, although there was no GPS and GSM coverage while the bear was inside the den. He spent the winter in a perfect bear denning area: remote rocky hillside in a small natural cave where he prepared a nice bed of fir twigs and leaves( see pictures below).



Markos den








After abandoning the den Marko spent a couple of weeks in that area, and then resumed his long distance walks. He crossed the highway many times and at different spots, exhibiting perfect orientation and landscape skills. Moving far in direction north and the west he is covering at least there bear management units. Without a GPS device such a bear would also be counted as at least three different bears by local bear managers. The device continues to make contact with satellites each two hours and sends us SMS after every 7 fixes



Engaged in the project are:

Tomislav Gomercic, Dr Goran Guzvica,  and Dr Josip Kusak





For more information please contact:

Prof. Dr. Ðuro Huber, Croatia,  Projectleader


Links: http://www.vef.hr/org/biologija/index.htm







Author’s articles as pdf (download)

URSUS 2002

Bear reintroductions: lessons and challenges                           PDF 92 KB

HUBER, D., et al.;

Causes of wolf mortality in Croatia in the period 1986-2001     PDF 183 KB

HUBER, D. et al.;
Zoo. Biology 1993

Food intake and masss gain of hand-reared brown bear cups PDF 743 KB

Ursus 2001

Brown bear litter sizes in Croatia PDF 468 KB

RANDI, E., et al.
Heriedity 1993

Mitochondrial DNA sequence divergence among some west European brown bear populations. Lessons for conservation
PDF 1330 KB

Acta Theriolocica 1993

Movements of European brown bears in Croatia PDF 303 KB

J. Wildlife Diseases 1993

Serologic survey for selected viral and rickettsial agents of brown bear in Croatia PDF 636 KB

HUBER, D. et al.
J. Wildlife Diseases 1997

Effects of sex, age, capturing method adn season on serum chemistry values of brown bears in Croatia PDF 954

HUBER, D. et al.;
Ursus 1998

Traffic kills of brown bear in Gorski Kotar, Croatia PDF 998 KB








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