Incredible journey: one wolf's migration across Europe

Slavc is a wolf. In 2011, he began an epic 2,000 kilometre migration across Europe from Slovenia to Italy via the Austrian Alps. Several months earlier, he had been fitted with a collar that allowed his movements to be tracked in incredible detail. I talked to Hubert Potočnik, the biologist whose work made this possible

• by Henry Nicholls
• theguardian.com, 
• Friday 8 August 2014

It has been estimated that there are now around 10,000 wolves in Europe. Photograph: tbkmedia.de/Alamy

Every year, Hubert Potočnik and his colleagues at the University of Ljubljana in Slovenia capture and collar a number of wolves in order to get a handle on the movements of these much-misunderstood creatures. In July 2011, he collared a young male that became known as Slavc. In June, I spoke to Potočnik for a feature that appears in New Scientist this week and he told me about Slavc’s extraordinary journey across Europe. What follows is an edited transcript of the interview …

HN: After you captured and collared Slavc in July 2011, he stayed with his pack for several months. Then, on 19 December 2011, he began to move. How did you know?
HP: We knew something was different because the GPS points showed that he had crossed two large motorways far outside of his natal territory.

Tell me about these collars. How do they work?
The collar is equipped with three types of different technology. It has a GPS receiver, a GSM modem to send SMS and also with a VHF radio transmitter as a back-up. We programme all our wolves to send a GPS signal every three hours, so we get about seven locations a day to give us continuous location sampling data.

Hubert Potočnik fits Slavc with the collar in July 2011, a device that will reveal the wolf’s incredible 2000-km migration from Slovenia to Italy. Photograph: Nina Ražen

What if the wolf can’t get a signal? Do you lose a datapoint?
No, because the collar has a special memory storage. All locations are stored and when the animal gets a signal again, it sends packages of seven locations per SMS. Sometimes we didn’t get any data for 3, 4, 5 days. Then after that we got six or seven SMSs with about 40 locations from the previous days.

The first motorway Slavc crossed was the A1 between Trieste and Ljubljana. How much of an obstacle would this have been?
It’s a fenced motorway. Wolves can only cross these highways on underpasses or overpasses or along the rivers. He crossed the A1 motorway on an overpass.

What happened next?
The last location that we got on that first day was from the backyard of a house in the middle of a small town called Vipava. Our first thought was that he had been poached. While we were discussing what to do with a wildlife manager from this region, discussing whether to call the police and so on, we got another location which showed the wolf was moving further and further.

He crossed another motorway, the H4?
It was quite easy. There is a 150 metre-long viaduct.

What time of day was he moving?
Typically he moved through these open areas during the night-time. But not always. For example, he spent three days in the forest near Ljubljana international airport and on the morning of the last day, he passed through an open area and headed towards the Alps.

What else did you discover about his stay near the airport?
At every place he stayed for more than three hours, we went to investigate and we found that he’d caught two foxes there. Our colleagues from Austria and Italy really got involved in this communication and sampling and anlaysing what he was doing on the route, collecting spray and so on.

At that point, he wasn’t far from Ljubljana University. I don’t suppose you saw him did you?
No. Over the course of his entire migration, we had only one report of a possible wolf sighting that might have been Slavc and that came from Austria.

Look closely. Slavc heads off through the trees shortly after recovering from his anaesthetic in 2011. Photograph: Hubert Potočnik

As Slavc passed through this very human landscape, how worried were you for his safety?
Along his route we were scared that someone would shoot this wolf, thinking it was a stray dog because of its collar. We tried to communicate through the media, local papers and inform especially hunters about the wolf with the GPS collar.

Apart from the motorways, can you identify two other significant obstacles that Slavc faced over the course of his migration?
The Drava River was certainly a major obstacle. He actually crossed it at a spot where the Drava is 280 metres wide. He swam. There is no bridge and we got riverside locations on one side of the bank and on the other. The only explanation is that he swam and crossed the Drava at that very wide part.
He also made his way across some really high mountains, entering a closed valley in the middle of winter where the lowest pass was 2,600 metres and the snow would have been about six metres deep. There were really extreme conditions at the time.

Then he made his way into Italy?
When the wolf entered Italy I got an email from an Italian colleague about video footage of possible wolves in the Lessinia Natural Regional Park. We started joking that Slavc was going there and would meet a female, because from the footage it looked like a female because of the way it urinated.

But he carried on past Lessinia?
Yes. He arrived in the Valpolicella region just north of Verona – greenhouses and vineyards – in March 2012. That was the first time this wolf killed a domestic animal on his route. He killed there, I think, two sheep and a goat. He stayed there for 12 days, probably because there was a private animal park and the owner had three captive wolves, one female and two males. But then he moved back to the north, and entered the Lessinia Natural Regional Park. It was April and we had exact GPS locations and we asked a park manager to go and check the tracks in the snow. When she got to the spot, she found the tracks of two canids, the first indication that Slavc had actually met the female.

In zig-zagging his way from Slovenia to Italy, Slavc is estimated to have travelled some 2000 km. Photograph: Hubert Potočnik, University of Ljubljana

You had programmed Slavc’s collar to drop off in August 2012. Why?
We expected that the collar batteries would run out at around this time. Besides getting some additional data stored in the collar, it is ethical to release a collar from such an animal.

But Slavc is still in Lessinia with the female (who became known as Juliet)?
As far as we can tell. Slavc and Juliet had at least two cubs last year because they were captured on camera traps set around their territory and on this video it was possible to see two pups. The information from this year is that they probably have another litter.

Lessinia Natural Regional Park just north of Verona. As far as we can tell, Slavc is still out there. Photograph: La Casara Caseificio/flickr

How would you sum up this experience?
There are lots of data about long-distance dispersal of wolves but there are very few cases where we have had the opportunity to follow an animal in such detail. Following Slavc across Europe offered a rare insight into the secret life of the wolf. It was one of the most amazing events in my life.

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