The Otters’ Tale. Simon Cooper
the father or another jealous male, nobody is entirely sure, but it surely happens and in all probability, as indicated by DNA matches, it is a bit of both. The fact is, this infanticide happens more often than we might like to believe. The reasons? Again, we don’t really know, but one can best assume that the mothers would not have evolved such a protection strategy without good cause. For otters the genesis of single parenting may have many reasons.
But spraints are more than just markers of territory; they are, in twenty-first-century jargon, food management tools, used by otters in all sorts of ways. Firstly, the spraint can say ‘I’ve just fished this pool, so give it some time to recover or we’ll kill the goose that lays the golden eggs’. Or secondly ‘Don’t waste your time and effort. I’ve caught all there is to catch’. Conversely, a pile of spraints, the most recent a little old, tells the otter that historically this is a productive spot now ripe for hunting. And no spraints either mark virgin or barren territory – proceed as you choose. Likewise, the contents of the spraint, be it the remains of fish, eel, crayfish and so on, tell of what there was, and maybe there still is, to eat. Kuschta was still a few months off appreciating the final piece in this spraintology jigsaw, which tells of females ready to mate and males on the prowl. Her time for this would come soon enough; for now she was struggling to find that elusive home territory.
If you sat an otter down to discuss the whys and wherefores of territory, the first words out of its mouth would most likely be ‘It’s complicated’; for Kuschta and her kind the enforced itinerant months were a progression from ignorance to understanding. When she was young the home patch that her mother had carved out was uniquely theirs; as far as she was concerned, the otter world did not extend beyond her immediate family. If other otters, including her father, strayed close, her mother would ward them off long before they could approach the pups. But now, on the road, she had to negotiate her way through a competing world.
To the human eye it is nigh on impossible to tell where the territory of one otter starts and another ends. There are no clear dividing lines; otters are certainly no respecters of man-made boundaries and there is little in nature that will hinder their progress. Otters are legendary for the ability to cover enormous distances in a single night; twenty miles is well within the scope of most, but herein lies the problem – that twenty miles is along a river, inevitably passing through a multiplicity of other territories that rightfully belong to other otters. But our mustelids have created a social policy that some humans could do well to learn from. At the core is the family territory, which is sacrosanct. It is always accepted that other otters will ‘pass through’, but woe betide any that pause or, worse still, try to stay. There is no excuse for ignorance; those spraints are flags enough to say who lives where and why. Single female otters, on the other hand, are more relaxed; after all, they don’t have pups to feed or defend so their territories are looser, overlapping at the edges. That said, they will have carved out a portion of the territory that they regard as ‘theirs’, expecting other otters to keep away. Males spread themselves much wider, their territory taking in maybe three, four or five females’ homelands, which they continually traverse, taking as much as a week to cover the entire area. Of course, this assumes there is only one dog otter in any given super-territory. But nature would not allow that – replacements and competition are always required. There will be more than one male sharing the territory, a potentially ruinous situation with competition for land, females and food. But otters have evolved a daisy-chain hierarchy where each lesser male follows in the footsteps of his immediately superior male, organising his life so he precisely avoids meeting the others. Of course, there are clashes, violent fights and changes in the order. No otter chooses to be of lower caste, but, given a death or some other departure, there will be a shuffling of the pack.
It is a fascinating animal culture; despite being solitary creatures, otters as a breed have survived for 20 million years because, probably without realising it, they look out for each other. Avoidance saves wasteful territorial disputes. Designated family homelands allow pups to thrive. Complicated spraint markings spread out the population, avoiding overcrowding, preserving food stocks and limiting disease. Wandering males mix up the gene pool. For the perfect evolution you could not write a much better script – it is just a shame, as we will see later, that humans came into the midst of this with near-fatal consequences.
Winter
As far as the weather is concerned, otters don’t worry unduly about the seasons; they are perfectly adapted to anything the British climate might throw at them, unlike, say, their tiny, semi-aquatic, fellow river dwellers the water voles, which are easily wiped out by a spell of damp weather, floods or the sudden arrival of a predator. Being at the top of the food chain helps, but, more importantly than that, the otter frame is honed for survival. You might have thought that, for an animal constantly in and out of the water, blubber was the key to insulation, like, say, a seal, but otters carry just 3 per cent of their body weight in fat. In seals it is more like 25 per cent, which is close to that of the human body. So what is it that keeps otters warm and dry?
A clue lies in the luxuriant fur which the otter, when not swimming or sleeping, is frequently grooming. To start with, otters generally look close to black when wet, but actually, when dry, their fur is more of a brown colour and incredibly soft to the touch. Kuschta’s Californian sea otter cousins have the densest fur of any animal on the planet, at 140,000 hairs per square centimetre. On its own, that figure doesn’t mean much, but when you reckon that the arctic fox, one of the most durable survivors of polar winters where the temperature may drop to as low as -20°C (-4°F), has fur with a mere 20,000 density, then the British otter, even though it trails the sea breed at 80,000, has a pelt for life. If you are wondering about us, a density of 300 on the human scalp tells you everything about the importance of hats.
Kuschta’s fur, like that of a polar bear and other mammals which are constantly immersing, is dual-layered. The top layer consists of outer guard hairs, which are thick and long and form a partial barrier to keep the fur beneath dry. As she climbs out of the water, Kuschta’s pelt will look anything other than smooth and sleek, but rather spiky, the coat almost like that of a hedgehog. This is because the hairs combine in little arrows to draw and drain the water off the body. But it is the underneath, the under-fur, the really dense stuff, where the otter is so truly well adapted for life in a river. Regardless of any density quotient, the ultimate test of the under-fur is that in whatever direction you stroke or pull at the half-inch hairs, you will not see the skin below.
However, the fur alone is not enough to insulate the otter. It takes one other crucial component, namely air, which, once trapped between the hairs, keeps out the cold – a sort of mammalian double-glazing – hair, air and then more hair. Grooming is, of course, about drying out and keeping clean, but it is equally for puffing up the under-fur to let air back in. And it’s a lot of air. To track an otter swimming underwater, watch out for a tell-tale line of air bubbles rising to the surface – wherever the otter goes, the bubbles will follow. For otter hunters it was a tracking gift from heaven and something the otter cannot avoid, for the bubbles are not created by breathing but by the pressure of the water gradually squeezing the air from the pelt. And because of this there is a definite time limit as to how long an otter can spend in water. After about half an hour the air has gone and both layers of fur are completely sodden, the cold water pressing against the skin, sucking heat from the unprotected body. Again, otter hunters knew this. If they could keep the otter immersed for long enough, regardless of how many times it surfaced for air (they can hold their breath for up to four minutes but rarely do so for more than 30 seconds), hypothermia would set in, hastening the end. Conversely, in the heat of a summer day, lounging on her couch, Kuschta would be content to leave her damp pelt well alone, the slowly dissipating air allowing her to keep cool, her coat fluffing and lightening to a more roan brown the longer she lay.
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