Sunday 23 June 2013

Caprines: Browsing Goats of the Western Mountains

Alpine chamois
The caprines as a whole can be divided into two groups, depending on which of two different lifestyles they happen to follow. The best known of these, since it is the lifestyle of sheep and "true" goats, is that of the grazing caprines.

Grazers feed fairly indiscriminately, munching down lots of grass and similar plants. In the case of the caprines, they survive in marginal habitats by eating pretty much anything that's available. They range across large areas in search of food, and adopt safety in numbers by packing themselves together in herds. Today, the great majority of caprine species adopt this lifestyle, and it's often what we think of when we think of goats and sheep.

But it appears that, in the evolutionary history of goat-like animals, it's a relatively recent innovation, one that was given a significant boost by the arrival of the Ice Ages. Before that, goats had adopted a rather different lifestyle, and there are still a minority of species - perhaps no more than five - that still live this way.

These apparently "primitive" goats were once grouped together in their own tribe, and given impressive sounding technical names like "rupicaprines" or "naemorhadins", but it's now less clear that they're really related. Instead, they represent at least two evolutionary lines within the goat-like animals, each a relic of the distant past when all goats were like this. Around them, some of their relatives switched to grazing, and, in the long run, proved the more successful.

No longer able to use those technical names, when we need to refer to these animals collectively, to distinguish them from the grazing caprines, we call them "resource defenders". Resource defenders are essentially browsing animals, picking out higher quality food, rather than just eating anything in sight. This requires them to live in the relatively small regions of their mountainous homelands where a good range of high quality food is available. They stick to these areas, defending them from others of their own kind, and as a consequence, they don't tend to travel far.

They also live in much smaller groups, since there's less decent food to go around. They tend to be physically smaller, too, and with smaller horns compared to most of their grazing kin. For reasons that are less clear, many of them - although not all - are also more brightly patterned than the grazing caprines.

In Europe, at least, the best known of these animals are the chamois. They are found across the more mountainous regions of southern Europe, but not in the north, where it is too cold for there to be a significant quantity of high-quality food to defend. There are two species of chamois, with the more widespread one being the Alpine chamois (Rupicapra rupicapra).

As their name implies, Alpine chamois are found across the Alps, but they are also found through much of the Balkans, in the Carpathian and Caucasus Mountains, and in north-eastern Turkey. As a result, it is sometimes called the "northern chamois", or (rather more rarely, outside of Wikipedia) simply the "chamois", as if it were the only one. There are at least five subspecies, perhaps more, distributed across the various mountain chains of its range, and its even possible that the Asian and Carpathian forms are entirely separate species - certainly, they can't be interacting much with those in the Alps or the Balkans.

One interpretation of the relationship
between chamois and Rocky Mountain goats
With their black-and-white striped faces, and distinctive, hook-shaped horns, chamois are easy to tell apart from other kinds of goat, although the individual species are extremely similar to one another. They have dark, almost black, coats that turn brown in the summer, and are slender and agile animals. Although fully-grown males are noticeably larger than females, both sexes fall more or less within the size range of female wild goats, making them significantly smaller than the billies.

They inhabit areas around the treeline, heading into woodlands to avoid bad weather, and out onto the alpine meadows in better conditions. While they are fairly territorial, maintaining remarkably small home ranges, they do move to different areas through the course of the year. In summer, they can be found at high elevations, between 1,500 and 3,000 metres (5,000 to 10,000 feet), feeding on herbs and flowers in the open meadows. Around October, when the first snows begin to fall, they head downhill, typically between 800 and 1,500 metres (2,400 to 5,000 feet), although they can go even lower if the conditions are right.

Leaves from trees and bushes are often a significant part of their diet while sheltering in the woodlands, although, like other goats, they also eat grass. Indeed, there is a considerable overlap between the types of food they eat, and those eaten by domestic sheep. In areas where domestic sheep roam freely in the same regions as Alpine chamois, there is evidence that the latter are forced into eating lower quality food, such as sedges, rather than the juicier food that they would normally consume. This is particularly significant, since it is the quality of food, rather than the volume of it available, that most affects the growth of chamois.

As "resource defenders", chamois live in much smaller herds than most other goat-like animals. Herds rarely contain more than six or seven adults, and then only when females are grouping together to protect their kids. For the rest of the year, female herds are even smaller, and the males don't live in herds at all, living solitary lives defending patches of land of just 1 km2 (250 acres) or less. Like most caprines, they try to stay close to rocky cliff-faces that are simply too steep and dangerous for predators to enter, and they are incredibly agile, leaping between terrifying precipices with ease. Inevitably, because there is little food on the side of a cliff, they have to venture into the open from time to time, and thus do fall prey to wolves and lynxes, where those share the same area.

Alpine chamois breed between November and December, allowing them to give birth, after a 165-175 day pregnancy, to their single kid between May and June, when the food is at its best. The breeding season is about the only time that males interact with one another, conducting fierce battles to establish their supremacy, and, as rutting males are wont to do, forgoing food to spend more time on amorous pursuits.

As a species, Alpine chamois have managed to cope with the presence of humans reasonably well. They may be forced into less accessible, and less nutritious, meadows by the presence of sheep, and they are hunted both for their meat, and for the particularly fine "shammy" leather that can be made from their hides. There have been some studies on how they have been affected by global warming, as the Alpine glaciers retreat, but the results are somewhat mixed. For example, while warmer winters seem to benefit the kids, presumably because the temperatures alone make it easier for them to survive, the increased snowfall that they bring is bad for the adults. It's also apparently the case that, while, like most cloven-hoofed animals, they can see blue and green (but not red), they don't seem unduly bothered by the brightly coloured coats of tourists wandering through their mountain homes.

Some individual populations, however, have fared less well. In the Balkans, populations are scattered and declining, while one subspecies is restricted to a single mountain in the French Alps. Worse still is the condition of the subspecies native to the Tatra Mountains on the border between Poland and Slovakia; less than 200 survive, and they are on the verge of extinction.

Pyrenean chamois
Like the Alpine chamois, the Pyrenean chamois (Rupicapra pyrenaica) is not restricted to the mountain range for which it is named; populations also exist in the Cantabrian Mountains of Spain, and in the Abruzzo region of the Apennine Mountains in Italy. The Italian population represents a distinct subspecies at least, and it has been suggested that both it and the Cantabrian population may be entirely separate species from the 'true' Pyrenean form. If, as is commonly thought, they really are only one species, then the obvious alternative name of "southern chamois" presents itself, and is quite popular.

Physically, Pyrenean chamois are extremely similar to their Alpine kin. They are slightly smaller, and typically somewhat paler, sometimes with creamy, rather than white, markings on their faces. But, in terms of physical appearance, that's about it, and it isn't always easy to tell them apart. Their habits are somewhat similar, too. Like Alpine chamois, they head to high pastures in the summer, and lower woodlands in the winter. Those that can find low altitude pastures in winter will head further downhill to reach them, but, for many populations, this isn't an option. In general, they like the same kind of terrain, with a good variety of plant food, and nearby cliffs in which to avoid predators.

At least in the Pyrenees, though, there are few predators to fear. Eagles and foxes may take off the occasional kid, but populations are more at risk of disease outbreaks than they are of being eaten by wild animals. In many places, this leads to a higher population density, and it seems that the all-female herds are larger as a result. Indeed, herds of twenty or so individuals are quite common - something unusual, although not unknown, among the Alpine species. The herds form in part by the ongoing social interactions between mothers and their kids, and between kids in the same herd, while adult males and females try to avoid one another outside of the rut.

Although the Spanish and French populations of Pyrenean chamois are hunted, strict controls are enforced, and seem to be working; neither the 'true' Pyrenean, nor the Cantabrian chamois appear to be at any risk, and population numbers are high. For a long while, the Italian subspecies (or species) seemed to be a different story. Completely isolated from its more westerly kin, and found only in a relatively small area, they nearly went extinct during World War II, and there were still only 400 or so alive in the 1980s. Since then, although they remain potentially vulnerable, numbers have nearly tripled, and are continuing to increase.

Taken as a whole, it's thought that chamois originated in Asia, heading east into Europe before the Ice Ages separated the northern and southern populations into the two (or more) species alive today. However, in 2011, analysis of the Y chromosome, which traces male ancestry, seemed to show the opposite pattern. According to this study, chamois may actually have first appeared in Spain, then spread eastward, hopping from mountain range to mountain range as the Ice Ages came and went. If so, the Pyrenean, not the Alpine, species may be the older one, although there's no evidence that the one evolved directly from the other.

Quite how the chamois relate to other caprines is also unclear. Some studies seem to show that they're related to Barbary sheep and Arabian tahrs, and thus probably closer to goats than to sheep. (Which certainly looks to be the case superficially, although that's probably more to do with their similar habitat than anything else). Others, however, show the chamois as an outgroup, a vestige of a primitive population of caprines that left no other descendants, and has no particularly close relatives within the caprine subfamily.

Rocky Mountain goat
Older schemes, however (which still have some support from recent analyses) argued that one of the closest relatives of the chamois was the Rocky Mountain goat (Oreamnos americanus). Although there are some points of similarity, for example, the presence of a scent gland on the back of the head, relatively small horns, and adaptation to cold and mountainous landscapes, in most other respects, Rocky mountain goats look and act quite differently to chamois. Unlike the beardless chamois, for example, both male and female Rocky Mountain goats have beards. In fact, their actual relationships to other caprines are even more obscure than those of chamois, with no consistent picture arising from the various studies conducted.

Often called by the shorter, but somewhat uninformative, name of "mountain goat", this is the only caprine native to North America that isn't a sheep - although, technically, it's not a goat, either. They're found mainly in Washington, Idaho, western Montana, British Columbia, and southern Alaska, although there are also native populations in neighbouring parts of Oregon, Alberta, and Yukon. Today, though, the picture is somewhat confused by the artificial introduction of the species to other parts of the American west, such as the Black Hills of Dakota, and areas as far south as Colorado, Utah, and Nevada.

Rocky Mountain goats are big animals, as large as some of the largest ibex, with powerful, muscular builds and a pure white, shaggy coat. As this bulk indicates, they are only "resource defenders" when the weather is particularly dreadful and defending what they can find is especially important; most of the time they are just as much grazers as real goats and sheep are. Like other grazers, they live in sizable herds, often at least thirty strong, although they can be much larger. Their home range is far larger, too, up to about 25 km2 (10 square miles), although it depends a lot on the local terrain.

They live in freezing mountainous terrain, typically near the treeline, exploiting both sparse woodland and steep meadows of treeless tundra. They can be found as high as 2,700 metres (9,000 feet), but the further north they are, the lower they are likely to be. Indeed, in Alaska, parts of the coastline are so rocky and cold that they can be found almost down to sea level. They move far less than most other caprines over the course of a year, and some stay in the same territory year-round, toughing it out through the winter, rather than moving downhill to warmer climes.

Like chamois, and many other caprines, they breed in November and December, giving birth in the early summer after a gestation of 185 to 195 days. Twins, and even triplets, are known, but uncommon. There have been a number of studies in the reproduction of these animals, often evaluating how they balance their energy budgets in a harsh terrain where food is difficult to come by, and such things as social rank and access to the opposite sex are particularly important.

We know, for example, that, because males spend so much time attracting females during the rut, and so little time feeding, that those who can bulk themselves up beforehand are the most successful. We also know that not only are older females likely to give birth to larger, higher status, offspring, but they are also much more likely to give birth to males. This, presumably, is because older females make better, and more experienced mothers, and, according to the so-called Trivers-Willard Hypothesis, good mothers want sons.

Why so? Well, the reasoning is that better mothers are able to rear larger and fitter offspring, by providing them with more food as they grow. In a species like Rocky Mountain goats, where males mate with as many females as they can, having large sons is an advantage, because they will give you more grandchildren. But, if you're a younger, and less experienced mother, then your offspring will be smaller. If they're females, that's no problem, because they're going to be mated regardless, and you still get grandchildren, but small males will luck out in the mating stakes, since its the males that are fighting with one another. So a young mother wants daughters, who will at least give her some grandchildren, while an older one wants sons, who will give her a lot more.

It's not, though, that younger males don't give it a go. Unable to compete directly with their larger and more dominant brothers, they try to sneak into an established group and chase females to get them away from the stronger male. It's a tactic that many mammals in similar situations try, and, among Rocky Mountain goats, it's not really very successful, though evidently at least worth the attempt.

In fact, the social structure among Rocky Mountain goats is somewhat unusual, because, outside of the two months of the rut, it's the females that are dominant, with even younger females dominating the local males. The females themselves are highly aggressive, and establish a social ranking system early on that seems to stay with them for life, and is much based on age and experience as it is on physical mass or the size of their horns.

While the goats are preyed upon by brown bears, wolves, and cougars, the parts of America in which they live are so wild, compared with Europe, that they have little to fear from man. Certainly, they are hunted (albeit under strict licenses), and they do seem particularly disturbed by any nearby human activity, but, for most of them, there simply isn't any, and its a threat that exists more in theory than it does in reality.

[Pictures by Marcin Białek, Juan Lacruz, and "Darklich14", from Wikimedia Commons. Cladogram adapted from Yang et al 2013.]

2 comments:

  1. the picture of the pyrenean chamois is under a creative commons license, you should mention its author, Juan Lacruz. Thanks.

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    1. I did; it's in the note at the end of the article.

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