Sunday, 11 February 2018
Jackals on the Motorway
One key difference between a territory and a home range is that the former, by definition, is not shared with any neighbours. Of course, the animal might be social, living in herds, packs or other kinds of band, so that all members of the group share a single territory, but, again, it's not shared with outsiders. A home range, on the other hand, almost always overlaps with at least some others used by members of the same species, especially if they happen to be of the opposite sex. Breeding would be problematic if they didn't.
The requirements for a home range vary significantly between different species, but they're generally a trade-off between having enough resources to survive and (if female) raise young, and the trouble you'd have to go to reach those resources. Larger animals, as we might expect, have larger home ranges, as do those which live communally.
At some point, though, solitary animals have to leave home; if offspring stayed in the same home range as their mothers for all their lives, they would soon run out of resources. Sure, if your parents happen to die, you can inherit their home range, more or less, but that will only work for one child at a time. (It's somewhat different for social animals, although if a group gets too large it will have to split, and, anyway, they'll still want mating opportunities with somebody other than their own siblings).
This leaving home is called dispersal, and typically happens not long after the animal is old enough to fend for itself. And this is the means by which animals, slowly but surely, expand through all of the habitat that is available to them. As the world changes due to human activity, the areas into which animals can move are also changing. Often that's for the worse, as we turn open prairie into farmland, drain swamps, fell trees, and so on. But sometimes it can be for the better, if the animal quite likes the opportunities that, say, agriculture provides, or as a warming climate lets them move further north than they could have before.
(Obviously that last example has limitations. If you live on a mountain and have to move up slope to avoid the heat, the higher you go, the less mountain there is. If you live in the lowlands and really like the cold, eventually you're going to hit the Arctic Ocean. And so on).
Understanding how this expansion happens isn't necessarily easy, although, as with more localised studies on home ranges, our increasing ability to attach GPS trackers to animals without upsetting them is making it more so.
For instance, one animal that has been expanding its geographical range in recent years is the golden jackal (Canis aureus). As currently defined, this is an animal, very closely related to the wolf, that lives across southern Eurasia, from Myanmar in the east to Italy in the west. I say "as currently defined" because populations living across north Africa are now commonly thought to belong to a different species, the newly named golden wolf, although this isn't universally agreed on as yet.
Golden jackals probably arrived in Europe not long after the end of the last Ice Age, and originally inhabited some of the warmer coasts around the Aegean. Over the thousands of years since, they have expanded, establishing stable breeding communities across Greece, Albania, Bulgaria, Romania, and Croatia. Just in the last few decades, however, that geographical base has extended even further.
By the end of the 20th century, golden jackals were living and breeding across the whole of the Balkans, including Serbia and Bosnia. The entire population in Macedonia was wiped out in the 1960s... but, two decades, later they were back again. Further north, occasional individuals were spotted making forays into Austria, Hungary, and even Slovakia, although not for long enough to establish local breeding populations.
That's where most sources say that they can be found today. But, as the first two decades of the current century wind on, they don't seem to have stopped, and they're still moving further. By 2011, those occasional sightings in Hungary and Slovakia were becoming more common, and they were breeding in Austria.
By 2016, the Hungarian populations were permanent and well-established, and wandering individuals were spotted as far afield as Lithuania and Estonia, hundreds of miles to the north. (The local governments assumed that somebody must have transported them there, and launched a legal crackdown as a result, but there's not really any evidence for this). There have even been, admittedly unconfirmed, reports of golden jackals reaching the Netherlands and Denmark.
This sort of thing can have effects on the local ecology, and not necessarily for the worse. But, given that the jackals seem be doing it quite a lot lately, it would be useful to understand how they disperse from the home ranges of their birth. It's something we know a fair amount about for wolves, but the same can't really be said for the more obscure golden jackals.
In October 2013, researchers captured a young female golden jackal near the village of Lábod in western Hungary, and fitted her with a GPS collar. Over the next two and a half months, they were able to track her movements, confirming that she lived in a home range of about 12 km2 (4.6 square miles) just east of the village. This was an area she shared with other jackals, and, as she was only about eighteen months old at the time, and wouldn't have started breeding, she was likely helping her mother or another older female to look after any younger pups.
Suddenly, at the end of December, she wandered off, travelling 20 km (7.5 miles) to the east, towards a patch of dense woodland. She returned home just three days later, possibly not liking what she found. And then, the very next week, she was off again, heading north, and this time not returning.
Over the next few days, she kept moving, rarely stopping in any one place for any length of time. She travelled at night, across a region that, despite a few clusters of woodland, is mostly open farmland, criss-crossed by a number of roads. At one point, she walked right across the M7 motorway near Lake Balaton, realised that there were only marshlands on the other side, and, a few days later, wandered back again.
Overall, she spent twelve days travelling, covering a distance of 224 km (140 miles) in search of a new home. She found one, close to the village of Somogytúr, 61 km (38 miles) from her starting point as the crow flies, on the 17th January. There, she established a new home range, of about the same size as her original one. For a five weeks in April and May the researchers had great difficulty locating her at all - it turned out that she had established an underground den to raise a litter of pups, and this was blocking the GPS signal.
This is the first detailed study of a dispersal event in golden jackals to be published, with the researchers able to follow the precise movements of a single individual in real time. It is, of course, just one animal, so we have no way of knowing how "typical" she may have been. Indeed, if jackals have reached Estonia from the Balkans, 224 km is presumably much less than they're capable of with sufficient motivation.
But this all took place at the very edge of jackal habitation in Hungary, with this particular animal moving into an area largely uninhabited by her own species at the time, and successfully raising a family there. Nor is this some wilderness area; the presence of humans and agriculture didn't seem to pose the jackal any problems, and she even crossed a motorway twice. In all, this tells us that jackal dispersal is much more like that of wolves than that of, say, red foxes, which travel shorter distances, both in total and on a per-night basis. That she did so in winter is unlike wolves, which prefer the spring and autumn for such movements, but how normal that is is exactly the sort of thing that's difficult to tell from a single event.
If golden jackals can cross dense agricultural lands, and don't even care about motorways in their path, they're going to keep moving across Europe for some time to come. Watch out, western Europe - the jackals are coming.
[Photo by Raju Kasambe, from Wikimedia Commons.]