There are doubtless many zoos across the world, especially in poorer countries, where things haven't improved all that much. But, at least in the West, things have changed significantly. Animals frequently get the chance to roam in outdoor enclosures with grassy environments, rocks and trees to climb, ropes or other toys to play with, and so on. Furthermore, modern zoos do have an important role to play in issues such as conservation - there are species in the world today that would have gone entirely extinct had not some of them been kept in zoos. (For what it's worth, two mammal species - a deer and an antelope - are currently listed as "extinct in the wild" by the IUCN. Re-introduction efforts are underway for both, but it's a slow and difficult process).
But the fact remains that, no matter how well you try, and no matter how good your enclosure, it still isn't the wild. Physical boundaries prevent animals from roaming as far as they might like, the terrain is unchanging and at least partly artificial, the climate is almost certainly wrong for at least some of the exhibits, you can't forage or hunt for food as you would do naturally... and, if the zoo is to make any money, there are going to be noisy people walking past and staring at you. For some animals, given the loss of their habitat to farms or cities, this may actually be the best option that they can get, but it's never going to be perfect.
One of the key ways in which captive animals respond to this is through stereotypic behaviours. These are repetitive actions without any obvious purpose which the animal performs over and over again, and they aren't normally seen in the wild. In mammals, one of the most common such behaviours is pacing back and forth over the same patch of ground, although there are many others as well, depending on the exact species.
What's less clear is why animals should do this. There is no shortage of explanations, and it's clear that a whole range of different factors may be responsible, so it doesn't necessarily follow that there's only one reason. But if we can at least find out what makes it worse, then maybe we can learn something that might, if not eliminate the problem altogether, at least minimise it.
One of the most popular exhibits in any zoo that has them is surely the giant panda (Ailuropoda melanoleuca). Giant pandas are, of course, bears, although they are not very closely related to other living bears, and are typically placed within their own subfamily. On the other hand, they are no more closely related to red pandas than they are to, say, ferrets - apart from the fact that they both eat bamboo, the two kinds of "panda" aren't really all that similar.
The Chinese government, which keeps close tabs on this sort of thing, stated that, as of 2014, there were 396 giant pandas in captivity, compared with a wild population of around 1,800. Conservation efforts have generally been successful, so much so that they were officially downgraded from "endangered species" to merely a "threatened species" in April 2016. But even so, with so many in captivity, it would be good to know exactly which bits of the zoo environment affect their normal behaviour the most.
|The Panda House at Beijing Zoo|
Surprisingly, it turned out that the pandas engaged in more stereotypic behaviour when allowed outside then when kept indoors. Indeed, one of the more commonly seen behaviours in such instances was repetitively scratching or pushing at the door, as if they wanted to get back inside (or possibly, were hoping to get fed). This particularly happened when the weather got hot, something that increased the frequency of other stereotypic behaviours as well.
The natural environment for pandas is highland bamboo forest, where it tends to be relatively cool. Indeed, with their thick fur, they are probably less keen on high temperatures than low ones, all other things being equal, and we know from previous studies that they're less stressed out if they at least have the option of heading indoors whenever they feel like it. That was something they couldn't do under the regime at Beijing Zoo, and that loss of control might be as much a factor in their behaviour as the warmth itself.
Bright sunlight also led to more frequent pacing, although they were also less likely to paw at the door to try and enter the more dimly lit indoor enclosure. Their forest home would presumably have a more shady environment than the open ground at the zoo, so, while the pattern is less clear, it's again possible that bright sunlight made them uneasy. On the other hand, perhaps because all of the pandas in the study were born and raised wholly in captivity, the number of visitors didn't seem to affect them at all - they just seemed to be used to that.
What the study doesn't show is whether or not these stereotyped behaviours meant that the animals were particularly stressed by their habitat. To do that, you'd need to do something like measure their levels of the stress hormone cortisol. Stereotypical behaviour often does correlate with poor living conditions for animals, so it's an important warning sign, but it's far from the only one. Indeed, since it may be, in part, a coping mechanism, animals that don't show such behaviour may actually be the ones that are worse off in any given environment.
So were these pandas unduly stressed? We don't know, although it's surely the case that they'd be happier in the wild... assuming, of course, that they could find somewhere in the wild that was itself safe from human interference. With wild panda populations currently increasing, there are other species (many of them non-mammalian) that are a more urgent conservation priority than they are, but that doesn't mean that they are entirely safe.
Zoos do have an important role to play in science and conservation, but to do that it also behoves us to ensure that their exhibits are as comfortable as they can be under the circumstances. Checking up on their behaviour is just one facet among many that can help us do that.
[Photos by J. Patrick Fischer and "snowyowls", from Wikimedia Commons.]