|Got any apples?|
Humans change the landscape around them, merely as a product of how we live. In order for our own species to survive, for instance, we need farmland, and lots of it. That brings competition with local wildlife, even if we're trying quite hard not to. Planted fields, and even open ranchland, are a change to the natural environment, and that's sure to have some effect. And that's before we start thinking about urban development.
Still, even leaving aside the fact that we can't really do without cities and towns, some animals have done quite well out of them. The house mouse is a particularly extreme example, and essentially doesn't live in the wild any more. But many other animals live in our cities, and even find them a benefit. Think of rats, pigeons, cockroaches... okay, so perhaps they aren't our most welcome neighbours, but from their perspective, we're rather a good thing.
And then there's animals that do well on the fringes, in the suburbs, or patches of urban greenery: urban foxes, badgers, raccoons, and so on. There's a balance for these animals to draw, between the risks of, for example, being hit by a car, and the advantages of nearby rubbish bins. Many of them become nocturnal, even if they aren't naturally, because that's the best time to be out and about if there's lots of humans nearby.
These tend to be smaller animals, which can most easily escape our attention, and live in the gaps between our dwellings. But, in some parts of the world, larger animals from outside can still wander into urban areas. There's a cost-benefit analysis for them, too: one on the one hand, there's food, and on the other, they might die. Clearly, they're deciding that the former outweighs the latter, or they wouldn't be there at all.
One such animal that it would be hard to miss strolling down your street is the American black bear (Ursus americanus). Smaller and less aggressive than its brown relatives, it's still strong enough to make quite a nuisance of itself if it put its mind to it. They don't actually live in urban areas, of course, but they do wander in if they think there's food to be had. That's despite the fact that this is far from safe, even for an animal of their size. So why do they take the risk?
Perhaps they're just hungry. If that's the case, we'd expect them to enter urban areas mainly in years when there's relatively little food out in the wilds. A drought, for example, might mean that there are less tasty berries and so on around, forcing them to take a riskier approach to finding dinner. Or are the contents of the average American garbage bin so much tastier than freshly-picked fruit, that bears are willing to risk all just to get at them?
Between March 2009 and October 2010, Jerod Merkle and co-workers monitored radio-collared black bears on the outskirts of the city of Missoula, in Montana. They wanted to know what time of year the bears were most likely to enter the city, which ones were more likely to do so, and what they were doing there when they did.
In that part of Montana, the main sources of fruit that black bears eat are on the bushes roughly between July and September. So, if they're just going into town when they're hungry, that should be when we least expect to see them. But, in fact, it turned out that they were most likely to wander close to people's houses roughly between September and November. ("Close" being defined here as "within 100 yards" which is as close as Montana Fish Wildlife and Parks says you ever want to get to a bear).
So, bears went into town in, for example, September, when there was still plenty of wild food - such as honeysuckle and chokecherry - available out in the woods. On the other hand, they almost never came into town in, say, March, when fruit would still be in short supply, but presumably, garbage cans were just as full as at any other time of the year. Which means that, at least in this part of the world, they're not driven either by general hunger or by a love of left-over dinners. But if it's not the rubbish, what is happening between September and November that makes the bears take risks they wouldn't in, say, March?
Well, that, it turns out, is apple season. The city is quite a green one, and there are plenty of domesticated apple trees in the urban area, which are at their best between September and October. Indeed, when the researchers looked at the places the bears had been, they found fruit trees far more often than they found garbage cans. Perhaps the cans are a nuisance to get into, or the bears can't be confident of what they'll find inside, or the contents just aren't very tasty. They certainly do go through them at times, but they're more interested in the juicy apples that happen to be growing near houses.
They also noticed that most of the bears entering the suburbs were male. Indeed, on any given day in apple season, the odds that a male bear, somewhere, was wandering up to someone's house were over 80%. That could well be useful information, since the males tend to be more aggressive. As to why it happens, it may be that the males drive out the females, hogging the best food for themselves. If males attack their cubs, for instance, females might have good reason to avoid any place where they're common.
Of course, these sorts of finding won't apply everywhere, depending, in part, on such things as the local environment. They certainly won't apply to other species. For instance, a similar study by Brian Kertson and co-workers looked at cougars (Puma concolor) living near towns just east of Seattle. They found that interactions between humans and cougars were (fortunately, one imagines) rather rare, although the animals certainly attacked livestock, even in small suburban farmyards.
However, the cougars weren't particularly on the hunt for domesticated animals. Most of the cougars venturing into residential areas were relatively young, suggesting that they had recently left their mother and were on the search for somewhere to live. They tended not to stay long in any one area, leaving after less than three days. They seem to have been most interested in nearby patches of woodland, whether on the outskirts of small towns, or as green corridors running through them.
This sort of thing isn't a major issue in most parts of Europe or, for that matter, in downtown New York. But there are places where it does matter, as much to us as it does to the animals concerned. Nobody wants a hungry cougar prowling the leafy avenues of suburbia. It's not a common event, but, through studies like this, we can build up a picture of how humans interact with large animals and find ways to minimise it through urban planning and public education.
[Picture by Simon Pierre Barrette, from Wikimedia Commons]