Rain Down on Me: Wild Boar and the Weather

Wild boar (Sus scrofa) are very far from being an endangered species. They are found across continental Europe and Asia, and on a number of nearby islands, from the Mediterranean to Japan. We have no idea how large their global population is, but it's clearly pretty big, and they are common animals in many places. But even if their very existence isn't in danger, that doesn't mean that we have no need to figure out how to properly manage their populations in the wild, so as to cause neither humans, nor the boars themselves, any inconvenience.

This is in part because the influence of wild boars on humans is mixed. On the one hand, they can be quite a nuisance. They cause significant damage to crops, can spread diseases to farm animals (most obviously, pigs), and caused almost a thousand traffic accidents a year in northwestern Spain. Clearly, these are all good reasons to keep their numbers down, at least in places where humans are common - which, let's face it, mean pretty much the whole of Europe. On the other hand, wild boar are generally regarded as quite tasty, which, while it's not a great thing to be from the boar's point of view, does at least mean that hunters don't want to drive them away into really remote and inaccessible areas.

In fact, since they're quite a common animal, and there's no immediate risk of us driving them to extinction, modern hunting has, on balance, probably been more positive for the species as a whole than the reverse. (Although, clearly, it's kind of bad from the point of view of individuals, as is the popularity of bacon for domesticated pigs). Because of this usefulness to humans, wild boar were re-introduced to southern Sweden in the 1970s, having been absent for around 200 years, and their population there is currently on the increase. In Britain, the last couple of decades have seen breeding populations established in two or three places in southern England, despite them having been locally extinct since at least the 13th century.

But, if we are to maintain wild boar populations, whether as part of restoring the natural balance of European ecosystems, or just a desire for expensive sausages, we need to do so while minimising all those negative effects. In order to do this, we need to understand how wild boar live their lives, and how we, as humans, may be affecting that. But part of the problem here is that wild boar are pretty intelligent animals, which, even leaving aside the moral question of whether we should be hunting them in the first place, also means that they can adapt their behaviour to differing circumstances.

There have, of course, been many studies into exactly this, but it's difficult to generalise between them, so it's often useful to look at particular locations on a case-by-case basis. One such study, published last month, took a look at the wild boar of northern Italy, considering, among other things, how they are affected by hunting, and also, for what's apparently the first time, taking a detailed look at how they change their behaviour in different weather conditions.

The study took place at a nature reserve at Camaldoli in the province of Arezzo, Italy, just a few miles east of Florence. It's a relatively mountainous area, covered in oak forest, and inhabited by deer, foxes, and wolves in addition to the boar. While hunting is not permitted in the actual reserve, it is nearby, and, obviously, boar don't get on well with the local wolves, either. To conduct the study, nine adult boar, of both sexes, and all from different sounders (i.e. 'herds'), were fitted with GPS collars and their daily activity and movements monitored.

One of the first things that became apparent was that the boars were clearly nocturnal, basically staying up for the whole night, and sleeping during the day. The only time that most of them spent any significant time awake and active during daylight hours was during June and July - presumably because the nights aren't long enough at that time of year for them to fully feed themselves. (For an American comparison, Arezzo is slightly further north than Boston, so summer nights are shorter than you might expect).

The reason that this nocturnal activity is significant is that wild boar are traditionally thought of as diurnal animals, and, indeed, their eyes do not seem to be adapted for night vision. Now, eyesight in pigs is pretty poor in the first place, so this might not bother them as much as one might think, but it's undeniably true that one big advantage of only coming out at night is that you're far less likely to bump into a human. In fact, the study also showed that wild boar were more active on nights of the full moon, so it isn't just a case of "darker is better", but is more likely to be an active strategy to stay out of the way of humans.

This would not be unique amongst mammals. Just one example among many are chamois, which are thought to be basically diurnal animals that have switched to a nocturnal lifestyle to minimise the chances of human interference. It's interesting that this may mean that we're more scary to the boar than wolves are, since the latter quite like moonlit nights, and they certainly aren't absent from the study area. The obvious suspects here are those hunters wanting to turn the boar into sausages, but it's worth noting that the boar didn't seem to be any more nocturnal during the four-month hunting season than at other times of the year. Most likely, hunting harassment has been sufficiently sustained in the area that the boar never broke the habit of hiding from it, and try to keep to night hours to be on the safe side.

But what about the weather? Well, it seems that, when they were active during the day, it was mainly when the weather was either damp or relatively cool. Avoiding the heat of the summer sun does make sense for a large, hairy, animal, and has been observed in several other species. On the other hand, the boars also avoided the coldest parts of the night, so, in this respect, they're probably just trying to get comfortable. But why were they apparently happy to go out in hot weather so long as it was also raining?

It's possible that rain might put off hunters, but the same effect was seen simply with rising humidity, and, in any event, is mostly in the summer, while the local hunting season is in the winter. So that's probably unlikely. What may be more significant is that pigs don't have many sweat glands, and the ones they do have are basically for making scent, not for cooling down (that is, they're the sort humans have in their armpits and groin). This, after all, is why pigs like wallowing in mud. So, if you're a wild boar, and it's hot, being rained on is a really good thing, as it helps you cool down.

Even humid weather without rain is a help, because it might make the soil softer, and easier to root through, and it may also help improve their ability to smell things - something that's particularly important to pigs, since, as noted, their eyesight isn't very good.

This is just one area in Italy. Given their relative intelligence, and the range of different habitats and climates in which they live, wild boar may behave differently elsewhere - Algeria, India, and Finland are all examples of places home to wild boar that are very different to northern Italy. The principle of boar preferring rain when it's hot may hold generally, but may be far less significant where it either doesn't rain very much, or never gets very hot. And, if wild boar, left to their own devices, would prefer to be out during daylight (if not during actual sunny weather), exactly how they switch to other times of day to avoid humans may vary depending on where they are.

And on the extent of the local desire for pork...

[Photo by "Jinilmarkose", from Wikimedia Commons.]