Covid and the Landscape of Fear

Left to their own devices, animals will wander about wherever there is food or other useful resources to be found. They would be limited only by the physical properties of their landscape, such as the inability to cross a wide river or the presence of a barren mountain range. Reality, of course, is never quite this simple.

The earliest use of the term "landscape of fear" that I could find on a quick search referred to a study about how female college students felt while walking particular routes alone after dark. Put in this context, one can well understand why people don't necessarily pick the simplest or most direct route to their objective, and why there are certain places one might simply wish to avoid altogether.

I Ain't Afraid of No Owls

Northern bat

There is no particular reason why bats should be nocturnal. True, nocturnality has many advantages, but so does daytime activity; the real question is why so few bats fly during the day. I looked at this last year, where I mentioned that one of the main theories is that since birds evolved flight before bats did, the bats originally flew at night so that daytime predators, such as hawks and eagles, didn't try to eat them.

If so, it may be an effective strategy, since there isn't very much that eats bats on a regular basis. That isn't to say that there isn't anything, however. The bat hawk is, as its name implies, probably the single most specialised bat predator, but studies in Africa have shown that hobbies (which overwinter there), Wahlberg's eagles, and African goshawks also attack bats with some frequency, and they're probably not alone. In this part of the world, bats, as one might expect, take measures to reduce their risk of attack. Flying in large flocks may help, but it's also known, for example, that they avoid flying on moonlit nights, and, when they have to, they don't fly above the trees as they normally would, keeping themselves out of view.

Bats in the Daytime

One of the things that we can say about almost all species of bat is that they are nocturnal. Regardless of whether they roost in caves or under the branches of trees, bats sleep through the day, wake up around dusk, fly out to get their food, and return home when the sun rises. But, when you stop to think about it, why should that be?

Consider: the great majority of bats eat insects and, sure there are plenty of insects around at night. But there's hardly a shortage during the day, either. Swallows, robins, and thrushes are all flying vertebrates that eat insects, and you see plenty of those around during the day. While for fruit bats and other herbivorous species, it's quite obviously not going to make a difference. If birds are perfectly happy flying around during the day, why not bats? It's not even as if there are only a small number of bat species that happen to occupy some narrow niche; there are well over a thousand of them.

We're Up All Day to Get Lucky

One of the key characteristics that's often listed for the behaviour of a mammal species is what time of day it tends to be active. There are four basic options here, of which the most obvious are diurnality and nocturnality. The others are crepuscularity if it's most active around dawn and dusk but not in between, and cathemerality if it really doesn't care - often because it lives underground. But, either way, it's natural to assume that this behaviour is relatively fixed in an animal; either it's nocturnal or it isn't.

In reality, however, it turns out that this can have a lot to do with the circumstances. And, in the modern world, those circumstances are most likely to be shaped by... what else, but humans? 

The issue, of course, is that humans are for the most part diurnal. Which isn't much of a problem for animals that are naturally nocturnal, but can be if they, too, would prefer to be active during the daylight hours. What we see time and time again across the world, and across different mammal species, is that where humans are most likely to encounter wild animals, those animals shift their behaviour towards nocturnality to avoid the stress of meeting us too often.

The Raccoon Family: Kinkajous - the primate-like "raccoons"

Raccoons proper are well-known animals, both familiar and distinctive even to those of us living in countries where they are not native. Among the other members of the raccoon family, coatis are at least familiar to people in the southern US. Ringtails ("cacomistles") are probably more obscure, being smaller and mostly active high up in trees at night, but at least, they too, live in the US. The remaining species, however, live only in Latin America and it's probably fair to say that they are much less familiar to English speakers than those groups with more northerly representatives.

Perhaps the most distinctive, and certainly the most studied, of these is a genus with just one species: the kinkajou (Potos flavus). It was first scientifically described by Johann Schreber in 1774, in an earlier volume of the book in which he would later describe (among other things) cheetahs, snow leopards, and bobcats. While he was understandably clear those were all cats, the identity of the kinkajou was not so obvious. In the days before Darwin, this may not have held any deep meaning for him, but his conclusion was that his new animal was a kind of lemur.

The Raccoon Family: Cacomistles

Ringtail

While true raccoons and coatis were first scientifically described during the 18th century, the third member of the raccoon family that's native to the United States was not described until 1830, by Heinrich Lichtenstein - who later went on to found the Berlin Zoo. It's unclear (at least to me) exactly what he thought the animal was. So far as I can translate the original German, his original description says that it's somewhere between a civet and a coati in appearance, but also looks quite like a fox. Based on which, he gave it the scientific name Bassaris astutus, a mixture of Greek and Latin that roughly translates as "cunning fox".

The scientific name didn't stand, because it turned out that the first part of it had already been used for a kind of butterfly. Furthermore, while he originally referred to the animal by its Spanish name "cacomixtle", since the specimen he knew of came from somewhere near Mexico City, in English we now call it a ringtail (Bassariscus astutus) or, less accurately, a "ring-tailed cat". Even so, in many parts of the US, an Anglicised form of the Spanish name is still in wide use. 

Haring About

One of the reasons that there is such a large number of mammal species in the world is that many of them are restricted to relatively small areas. There are a great many species that can be found only in one place, perhaps because it's a remote island or otherwise physically difficult to leave, or perhaps because they have very specific requirements and can't traverse the terrain between the patches of land that meet them. Others, of course, may have lived across wider areas in the past, but are now endangered, perhaps because their land has been converted to agriculture or urban areas, or because they are seen as either especially tasty or a threat to humans or their crops.

On the other hand, many species are widespread with large populations and seem to be happy in a variety of different habitats. Often, these are animals with a broad diet, able to eat a range of different foods and still remain healthy - the red fox is a good example of this, especially once it started exploiting suburban habitats in the 20th century. Typically, they will not be as good at finding or processing these foods as those that specialise in one particular type but the fact that they can switch food sources easily makes up for this. Indeed, this can be a driver for evolution - an animal becomes really good at exploiting one narrow food source, out-competing the generalists, but the latter remain in the background and, when the world changes and the narrow food source is replaced by something different, become the basic stock from which the next round of specialists will arise.

Before Owls Ate Mice

Palaeoglaux

Most bird species are diurnal. Doubtless, if you're flying about and don't have sonar, as bats do, it helps to be able to see where you're going. Nonetheless, there are many exceptions to this general rule, and none are more obviously so than the owls.

There are well over 200 living species of owl currently recognised, ranging in size from the mighty Eurasian eagle-owl (Bubo bubo) with a wingspan of up to 180 cm (6 feet) down to the tiny elf owl (Micrathene whitneyi) with a wingspan of just 27 cm (10 inches). They are grouped into two closely related families; the great majority of species belong in the Strigidae family, with just 20 assigned to the barn owl family, the Tytonidae. While there are some internal differences between the two, the most visible in the living animal is that barn owls, unlike regular owls, have distinctive heart-shaped faces.

Both families have been around rather longer than most mammal families have, with fossil representatives dating back to at least the Early Oligocene, around 35 million years ago. The two families are, however, rather like pigs and peccaries, each others' closest relatives, together forming the order Strigiformes. Since few people would deny that a barn owl is, in fact, an owl, it's this order that's really the scientific counterpart of our everyday understanding of the word.

Gerbil versus Rattlesnake

Sidewinder

Deserts are harsh environments, and living in them poses animals a number of problems, not least of which are daytime heat and an absence of water. In order to survive in such a place, animals need to evolve suitable adaptations - extremely efficient kidneys to reduce water loss are one such example.

But the thing about deserts is that, while there are some geographic differences between them, the challenges of living in one are at least broadly similar regardless of which desert it happens to be. And while, say, the world's seas are all connected, the deserts aren't. So animals, including mammals, have had to evolve means of surviving in them several times over, re-developing the necessary features each time they encounter a new one.

Prehistoric Mammal Discoveries of 2017

Albertocetus meffordorum, the post-cranial anatomy of which
was described for the first time this year.

At the end of each year, I do a slightly different post to wrap up the blog for the season. The format of these has changed over the years, and this year, again, it's time to do something slightly different from previous occasions. Not that there haven't been some interesting new species discovered this last year, with, to my mind, the Skywalker gibbon (Hoolock tianxing) being the stand-out example. This was announced early in the year, having been discovered in the Chinese/Myamar border region by a group of researchers who were fans of a certain science fiction franchise ("tianxing" literally translates to "sky-walker" in Standard Chinese), and is likely already endangered.

But this year, instead of discussing just how many new kinds of bat we discovered in the last twelve months, I'm going to note that my posts on fossil mammals tend to be more popular than those on the living sort, and take a look at a partial assortment of scientific papers published on this subject in the last year that, for various reasons, didn't end up in my regular blog posts. So here goes.

Counting the Clouded Leopards

There's no definitive answer to the question of which group of wild mammals have the greatest public popularity, but there can be little doubt that the big cats are up there with the best of them. They are a popular subject for wildlife documentaries, and, for example, the BBC's Big Cat Diary ran for nine seasons (some under slightly different titles) between 1996 and 2008.

Because they're the easiest to film, living as they do in relatively open and accessible terrain, four species of big cat get the lion's share (ahem) of the televisual attention: lions, tigers, leopards, and cheetahs. But, of course, these are not the only ones. Taking a wider look, the cat family as it exists today has two major branches: the big cats, or "pantherines", and the "true felines". That latter group is the larger of the two, including not only the domestic moggie and such species as the ocelot, but even some relatively large animals, such as servals and bobcats. Perhaps more surprisingly, both the puma/cougar/mountain lion and the cheetah actually turn out to be "true felines" when you look at their evolutionary ancestry - in fact, they are closer to domestic cats than they are to, say, lynxes.

Bed Time for Wild Hamsters

Golden hamster

After the mice, the second largest family of mammals is the hamster family, with somewhere in the region of 600 known species. The vast majority of these species are, however, not hamsters, and I refer to it as the "hamster family" only because that is the literal meaning of its scientific name, the Cricetidae. Over half of the cricetids, for instance, are "New World mice" visibly more or less indistinguishable from the "true" mice of the Old World. Most of the remainder are voles, and a mere couple of dozen or so are actually hamsters.

The species most people think of when they think of hamsters is the golden hamster (Mesocricetus auratus), which is the animal commonly seen in pet shops. While a few other species are sometimes also kept as pets, most of the varieties named on the basis of things such as hair colour and length are just domesticated breeds of the golden hamster. They are found in the wild only in one relatively small area on the Turkish-Syrian border, just north of Aleppo. Which, right at the moment, does make it somewhat difficult to study their behaviour in their natural environment.

But then, given that there are so many of them in captivity, and that they aren't exactly obscure animals, you might think that we know pretty much all there is to know about them. Certainly, compared with many other species, they are well-studied creatures. Indeed, they are common laboratory animals, due to the ease of breeding them in large numbers and their apparent comfort in indoor environments. On the other hand, while there are obvious advantages, such as not being eaten by predators, hamsters do not naturally live in cages... so maybe they behave differently when given the free run of the countryside?

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.

By the Light of the Silvery Moon

Why bother being nocturnal? Being active only at night makes it much harder to see what you're doing, and while it's possible to develop good night vision to minimise the problem, this is evolutionary costly. Well, if you're a herbivore, the advantage of being active at night is that it's much easier to hide from predators, since, they, too, would have to evolve good night vision to find you. And, if you're a predator, the advantage is that at least some of your competitors won't be around at night, allowing you to snack on nocturnal herbivores and not have to share your food supply.

But this, of course, cuts both ways. For example, while darkness hides you from predators, it also makes it more difficult to spot predators coming if they have seen you. As so often, this leads to a balance, and different species taking advantage of different points on the continuum of possible behaviours.

We can see some of the effects of this in how animals respond to different levels of darkness. Not all nights are equal, after all. The most predictable change is in the amount of moonlight, with the night of a full moon being considerably brighter than a night without a visible moon. Somewhat less predictably, of course, there's the weather, unless, perhaps, you live in a desert where overcast skies are fairly unlikely. So, if you're a nocturnal herbivore, should you be more active on the night of a full moon, or less?

Bats v. Hawks

Bat hawk

There are not many animals that eat bats. Or, at least, that's often been the received wisdom. Bats only come out at night, fly through the air, where it's difficult to catch them, and many spend the day sheltering in caves that are difficult to access, and that rapidly become filled with so much bat poo that not much else is willing to venture within. But they don't all live in caves, they aren't the only things that come out at night, and, anyway, there's just an awful lot of them, so surely something must, in fact, eat them?

And, of course, the answer is "yes". In fact, there are actually quite a lot of animals that eat bats from time to time. In Brazil, for instance, snakes, especially tree-dwelling constrictors, have been reported to prey on bats. So do other vertebrates, from fish to mammals, and even a few invertebrates, such as, yes, really - giant centipedes. But, considering all that flying they do, it's perhaps unsurprising that the main predators of bats are, in fact, birds. And, among the birds, it's doubtless also not a great shock to discover that owls are the primary culprits.

For instance, it has been estimated that in Britain, at least 11% of all bat deaths (and probably more than that) are caused by birds. Around three quarters of those attacks are by tawny owls (Strix aluco), and 90% of all predation incidents on bats in Britain are due to owls of some kind. With 5% of predation incidents having nothing to do with birds at all, it nonetheless follows that a further 5% must be due to birds that aren't owls... and, of course, this is just Britain, where (for example) tree-roosting bats are quite rare.

When to be Awake

The activity patterns of mammals fall into three broad categories. Diurnal animals, such as humans, are active during the day, waking up in the morning and going to sleep at night. This has the obvious advantage that you can see where you're going, but does also make it easier for predators to spot you. The opposite is, of course, being nocturnal - active during the night, and resting during the day. The darkness may help hide you from predators, although you'll naturally need some means of finding your own food, whether its by exceptionally good eyesight (as is the case, for example, with owls), or relying on senses other than vision (as in bats). For animals in many areas, the simple fact that humans aren't around much at night may also be an advantage.

The third pattern is crepuscularity. Crepuscular animals are active mainly at dawn and dusk, resting both during the night and during the day. This gives the animals something of the advantages of both the other modes of activity, and it is rather more common than is often recognised. Such animals can keep out of the heat of the day, and find it easier to avoid predators in the twilight, but still have enough light to see by when they're searching for food.

For at least some animals, this is clearly a response to the lighting levels themselves, rather than just an instinctual daily rhythm of getting up twice a day. This is apparent because they also tend to be more active on bright moonlit nights, which give them enough light to see by long after they'd normally go to sleep. In contrast, its generally thought that truly nocturnal animals don't much like the moonlight, which eliminates some of the advantages that the darkness normally gives them.

It's not always as easy as one might think to work out whether an animal is genuinely nocturnal, or just crepuscular. But this can be important if, for example, you want to know how many animals of a particular species are around for conservation purposes. For a start, what exactly do we mean by "active"? Clearly, not being asleep is a good start, but given that, in the wild, you can't generally watch particular animals 24 hours a day, what exactly they're doing when they're awake may make quite a difference.

The North American river otter (Lontra canadensis) is the animal most Americans think of when they think of otters. They're the only species of freshwater otter in North America, and are found throughout much of the US and Canada. Americans often call it the "common otter" as a result, but this isn't terribly helpful, since that's exactly what Europeans call the European otter (Lutra lutra) - which, despite the name, is found everywhere from Britain to Vietnam. Otters form a natural group within the rather diverse weasel family, and there are many species besides these two, found in Africa, South America, and Asia, plus the sea otters of the north Pacific coast.

N. American     S. American     European      Giant
River Otter       Otters       Otter, etc.    Otter
     |              ^              ^            |
     |              |              |            |
     ----------------              |            |
            |                      |            |       Weasels
            |                      |            |          ^ 
            ------------------------            |          |
                       |                        |          |
                       |                        |          |
                       --------------------------          |
                                   |                       |
                                   |                       |
                                   -------------------------
                                               |
                                               |


The North American river otter is generally thought to be crepuscular. But it turns out that the story isn't quite so simple. In the recently published study, a number of otters were caught and radio-tagged in the Whiteriver area of Minnesota, then released into the wild and followed for about three and a half months. Crucially, the researchers looked at two different measures of the animals' activity. Like many mammals, male otters consistently wander across a far wider area than females. Indeed, in this case, males occupy home ranges of around thirty square kilometres (twelve square miles), and females only around a third of that. Since the males' ranges overlap with those of several of the females, this gives them plenty of mating opportunities, and this is also a fairly common pattern amongst mammals. On the other hand, otters are pretty social animals, and don't tend to fight each other when they meet or defend their territories aggressively.

So, one measure of activity is to see when radio-tagged animals are travelling between different parts of their home range, and their locations are being picked up by different receivers. This is the usual way that these sorts of studies are done, and an animal is fairly obviously active if it's moving from one area to another. The results showed that, as expected, the otters were most likely to move about just after sunset and just before dawn. Males moved about the most, especially during the breeding season, when they were actively searching for mates.

However, just because the otters aren't moving between different areas that doesn't necessarily mean they're asleep. So another possible measure is to look at the signal strength picked up by individual receivers. If that's changing a lot, then the otters presumably aren't sleeping in their dens, and must at least be doing something. When the researchers looked at this measure, they found that the otters were active throughout the night. So this means that the otters are basically nocturnal, and just travel the furthest during the hours of twilight - the rest of the time they're presumably foraging for food in specific locations.

In fact, when looked at in this way, both males and females are equally active; it's just that the females tend to stick to familiar hunting grounds within the river, rather than moving longer distances. Perhaps surprisingly, both sexes tended to be more active the colder the weather got. Most likely, they needed extra food to keep themselves warm, rather than staying at home out of the snow as a human might. Moonlight, on the other hand, made no difference to them at all. If you're swimming about underwater in a muddy river, it really doesn't matter how much moonlight there is anyway, and otters mainly seem to find fish using their sense of touch, rather than vision.

With nocturnal animals, you'd normally expect that they'd actually be less active during the full moon, something that's the case with many small mammals. This is largely because they're more likely to be spotted by predators when the moonlight is relatively strong, but that would be less of a concern for otters, which don't have that many predators, since animals like pumas and wolves tend not to follow them into the water.

However, its interesting to note that some smaller nocturnal animals don't seem to care about the moon, either. Another recent study showed that giant kangaroo rats (Dipodomys deserti) are, unlike most of their relatives, also equally active when the moon is full as when it is new. In their case, the suggestion is that, rather than just hoping predators don't see them, they are quite good at looking out for danger and then escaping at high speed before they can be eaten. For any animal that's good enough at doing that, the fact that they can see the predator coming when the moon is full might cancel out the increased odds of the predator spotting them, so that, all in all, it makes little difference.

Such exceptions to the general rules mean that animal behaviour isn't always as clear cut as one might think, even when it comes to something as basic as when they're awake and when they're asleep.

[Picture from Wikimedia Commons]