In many land habitats, climatic conditions vary only slightly within a region. In mountains, however, the average air temperature drops by about 1°C (1.8° F) for every 200 m (650 ft) gained in height, oxygen becomes scarcer, and the air becomes less effective at screening out ultraviolet light.
As a result, mountains can be divided into distinct zones, each supporting plant and animal life that is very different from that of the zone above and below. A wide range of animals live in the low-elevation foothills, but only the hardiest survive year-round in the harsh environment above the tree-line.
In temperate regions a mountain’s climate is relatively cool throughout the year. However, seasonal changes are much more marked than they are in the tropics.
At high elevation, above the tree-line there is a sudden burst of plant growth in spring and summer. Some animals migrate upwards to make use of this brief abundance of food, but others such as the marmot, are permanent residents between mid- and high-elevation, surviving the winter cold by living in burrows and by hibernating for up to 8 months a year.
High-elevation insects spend many months in a dormant state coming to life when warm weather arrives. For many, this dormant period is spent inside the egg, which hatches when the days lengthen and the temperatures rise. At tower elevations, the climate is warmer, and generally more like that of the surrounding land.
However, because the sloping, rocky ground is difficult to farm, the mountainsides often retain more of their tree cover than does flatter ground. In undisturbed conditions these montane forests are the natural habitat of large mammals such as pumas, bears, and deer, and also of a wide range of seed- and insect-eating birds.
Temperate mountains abound in birds of prey. Some, such as the peregrine falcon pursue their prey on fast-flapping wings, while eagles and buzzards soar high up riding on updraughts. One characteristic mountain species a vulture called the lammergeier, turns the mountain landscape to its advantage by carrying carrion bones aloft and dropping them onto the rocks to expose the edible marrow inside.
In the tropics. the generally warm climate means that mountain vegetation zones extend much higher than they do in mountain habitats elsewhere in the world.
For example. near the equator. trees often grow at elevations of up to 4,000m (13,200ft), which is why many tropical mountains are forested to their summits Above this elevation is the tropical alpine zone, an open landscape dominated by grass and some highly specialized plants. This zone is often above the clouds. which means that nights are cold and frosty and yet the sunshine is fierce.
Many tropical animals have successfully adapted to life at high elevation. They include the vicuna, which can be found up to 5.500m (18,100ft) in the South American Andes. and the yak. which reaches a record 6,000m (18.100ft) just north of the tropics in the Himalayas.
Birds also live at great heights: in South America. for example, mountain hummingbirds called Andean hillstars often eed at over 4,000m – 13200ft). The Andean hillstar‘s minute size means it sas diffticulty storing enough energy to enable it to survive the cold nights. To combat the problem. its nocturnal heartbeat slows down and its temperature plummets. conserving energy.
The cloud-covered forest below the alpine zone is the habitat of some of the worlds most endangered animals. They include the eastern gorilla — a species restricted to the mountains ot Central Africa — and the resplendent quetzal. a bird that lives in the cloud forests of Central America. The abundant moisture means that the forest zone also teems with many different species of frogs. living both on the ground and in trees.
LIFE ON MOUNTAINS
Life at high altitude can be harsh. Food is often scarce, the weather can be treacherous, and the thin air can make it difficult to breathe. However, there is also more space, relatively little interference from humans, and fewer predators than there are lower down.
Many animals are “incomers”, using high ground as an extension of their normal range, but there are also some that live only on high ground. In large mountain chains, many animals have a wide distribution; but isolated peaks are often inhabited by animals that are found nowhere else.
BREATHING THIN AIR
At 6,000 m (19,800 ft), air is half as dense as it is at sea level. As a result it contains only half the normal amount of oxygen – so little that anyone trying to breathe at this height would have difficulty remaining conscious.
Yet some mountain animals live even higher than this because they have evolved specialized body systems that enable them to get the maximum amount of oxygen into their blood. In the vertebrate world, birds are the unrivalled experts at high-altitude living. This is because air passes through their lungs in only one direction, not in and out, which ensures that a high proportion of the air’s oxygen enters the blood far more than enters a mammals bloodstream in the same conditions.
This fact is apparent from the height at which birds are capable of flying In the Himalayas, choughs have been seen fluttering around campsites at over 8,000 m (26,400 ft). and there are records of vultures colliding with planes at over 11,000 m (36,300 ft) — far higher than Mount Everest. Birds are unusual in being able to cope with rapid changes in altitude without experiencing any ill effects.
For mammals, moving from one elevation to another necessitates special adjustment by the body, which is achieved by acclimatization — a process that can take several weeks to complete. During acclimatization, the number of red cells in the blood slowly increases, boosting its oxygen-carrying capacity. This physical adjustment, which is shown by a broad range of mammals — including humans — is temporary.
If any animal moves back to lower ground, the process is reversed. However for mountain mammals, such as the vicuna and ibex adaptation to life high up is a permanent state, not something that can be switched on and off. When measured as a proportion of volume vicunas have 3 times more red cells in their blood than most other mammals, and the hemoglobin in their red cells is unusually good at collecting oxygen.
As a result vicunas can run almost effortlessly on the altiplano — the high-elevation plateau that runs the length of the Andes. Compared with mammals, cold-blooded animals such as reptiles have fewer problems with thin air because they use oxygen more slowly. For them, the main problem with mountain life is cold: if the temperature is too low, their body processes slow down, and their muscles have difficulty working.
Mountains seem almost purposely-made for soaring birds because strong air currents make it easy for them to gain height. For animals on or near the ground, moving about is not so easy. Many insects are wingless, and species that do fly usually keep close to the rock to reduce the risk of being blown away by the wind. For larger animals, the situation is even more hazardous for a single misguided move can lead to a fatal fall.
Many rock-dwelling mammals therefore have feet designed to prevent slipping. In Africa and the Middle East hyraxes — rabitsized grazing mammals — run over rocks and boulders with the help of each foot has a bare rubbery pad slightly raised in the center, and moistened by sweat. As a result, each foot works like a suction cup so the hyrax can cling to the surface of smooth rocks
Without slipping, hooves may seem far from ideal for climbing, and it is true that some hoofed mammals, such as horses, have great difficulty moving about on rocky slopes but in climbing mammals, such as mountain goats and klipspringers, hooves have evolved into perfect aids for moving about in mountains: they are small and compact, allowing them to fit onto narrow ledges and they have hard edges surrounding rough.non-slip pads.
These combined characteristics make for good grip in all conditions including rain and snow. Getting a firm grip is essential for moving on rock, but equally important is a strong sense of balance and head for heights.
Most terrestrial mammals are instinctively afraid of steep drops but, from an early age, mountain- dwellers show what appears to be a reckless disregard for their own safety. Adult chamois take 6 m (20 ft) leaps, and can run down near-vertical slopes as easily as they can run up them; and their young are able to keep up with them when just a few weeks old.
In tropical mountains, conditions are often much the same all year round, which means that animals can stay at one elevation all their lives, but in temperate mountains, seasonal changes affect the food supply. Winter is the critical time: anything that cannot survive the cold weather conditions and the shortage of food has to move to lower ground or hibernate until the return of spring.
Animals that are high at high elevations have a variety of ways of coping with the changes. Insects often enter a dormant state, called diapause, which puts their development on hold.
Many small mammals, such as marmots, survive mountain winters by hibernating, while many of those that remain active live on food stores accumulated earlier in this year Pikas, for example, gather up leaves and grass and build them into “haystacks” among the broken rocks around their homes. Before adding fresh supplies to a stack, they sometimes spread them out to dry in the sunshine which reduces the chances of the food rotting. For other animals, the first autumn snows are the signal to move downhill.
These vertical migrations are a common feature of mountain life in temperate regions, and they are demonstrated by a wide range of mammals and birds, from mountain sheep and deer to choughs and grouse. In many cases, the migration involves moving from the exposed mountaintop to the forests tower down but some mountain forest species also migrate.
Among these latter migrants are birds such as nutcrackers, which feed on conifer seeds. If the seed crop fails, they fly downhill in a form of sporadic migration called an irruption. Clark’s nutcracker, from the Rocky Mountains, is a typical example: normally found at up to 2,500m (8,200ft), it descends as low as sea level when food becomes hard to find.
As in most land habitats, a mountains animal life depends ultimately on plants, for plants provide food for herbivorous animals, which, in turn are eaten by a wide range of predators. However, some mountain animals make use of a very different food source — the cargo of small animals mainly insects, that are carried uphill by the wind to be stranded among the rocks, snow, and ice.
Most of these wind-blown animals are so tiny that they are practically invisible; yet they provide useful nourishment for scavengers that live above the snow-line. They consist almost entirely of invertebrates, such as spring-tails and show fleas, which can survive the very low temperatures of high-altitude winters.
During the depths of winter, they hide among rocks and moss, but when the weather warms up they can often be seen hopping: across banks of snow feasting on the debris that the wind has brought up from lower ground.