[MUSIC] What really determines the success of species adapted to mountain environments are not the individual adaptation strategies, but rather how all the pieces fit together. Let´s take a look at four different species and how they're adapted from top to bottom for life in high places. White-tailed ptarmigan are the smallest grouse in North America and well adapted to life at high elevations. In fact, it's the only bird in North America to reside permanently in the alpine zone. One essential adaptation of ptarmigan is that they change the color of their feathers seasonally from white in winter to speckled brown in summer allowing them to be camouflaged from predators year round. During winter, their white plumage extends to cover their feet providing valuable insulation to their extremities, so less heat is lost to the cold snow. Feathers on their feet also act as snow shoes to help them navigate the deep snow. Insulation provided by their feathers and layers of fat accumulated during summers means they can effectively thermoregulate even in extreme cold. Ptarmigan can maintain body temperatures around plus 40 degree Celsius throughout the winter despite temperatures that dip well below freezing. They even have feathers around their nostrils to warm air prior to entry into their respiratory tract. Behavior adaptations of ptarmigan also enable them to control their temperature across seasons. The sedentary lifestyle of ptarmigan helps them conserve energy during winter since they tend to avoid flight and sit still for long periods. Ptarmigan have also developed unique ways to take advantage of the abundance of snow at high elevations. To cope with the limited supply of liquid water during the winter, ptarmigan eat snow. In the winters, they roost in snow banks to keep warm and in summer they bathe in snow to keep cool. There are 14 species of marmots in the world. Six in North America and eight in Eurasia. These are large rodents in the squirrel family and they are expert hibernators. In fact, marmots spend around 200 days a year in hibernation. They enter their burrows called hibernacula, as early as September and they don't emerge again until April or May. To provide extra warmth over the long winter, marmots insulate their burrows with dry plant material. During hibernation, marmots cycle through long periods of torpor that are briefly interrupted by bouts of wakefulness. During these recovery periods, increases in metabolism allow animals to become active. When torpor is induced, marmots decrease their set point temperature from around 40 degrees Celsius to less than 5 degrees Celsius. Almost matching ambient temperature in their burrow. Marmots rely entirely on their fat stores to survive. In the late spring, when marmots emerge from their burrows, they reproduce and then dedicate their time to eating and packing on as much fat as possible. They often double their mass in preparation for another winter of hibernation. The social behavior of marmots is also a useful adaptation that helps them keep warm during winter and avoid predation during summer. Huddling together in social family groups while they over winter, reduces heat loss and increases their survival. Above ground, on the exposed alpine tundra where marmots forage, they're very conspicuous to potential predators. As a result, they're continuously vigilant to detect danger and will produce high pitched whistles to alert colony members, so they can retreat to safety in their burrows. >> [SOUND] >> Their unique adaptations to the alpine also make marmots a very useful sentinel species, for helping us to understand the impacts of other environmental changes in mountains. For example, the most endangered mammal in Canada is the Vancouver Island Marmot. A census in late 2003 resulted in a count of only 21 wild marmots on Vancouver Island. The main cause of the population decline was attributed to increased predation associated with habitat changes caused by clear cutting, followed by rapid forest regeneration. But over the past 15 years, marmots have been released from captivity into the wild and the population is recovered to almost 400 individuals. This is a huge conservation success story and a good indication that marmots can adapt to changing conditions. In Europe, alpine marmots were successfully introduced in the Pyrenees in 1948 where the marmot had disappeared at the end of the Pleistocene some 10,000 years ago. They were first released by French hunters from the Alps as a food source for brown bears and golden eagles, in order to reduce predation on Chamois, a goat antelope genus native to the mountains in Europe. However, the marmot populations in the Pyrenees have exploded to over 10,000 individuals from an initial release of just 400. And now there are even questions about whether these huge numbers are actually causing damage and unbalancing the ecosystem. The successful introduction of alpine marmots into the Pyrenees provides considerable evidence for the adaptability of this species to survive in mountain environments. However, marmots may also impact the floor of the alpine and sub-alpine meadows. And may compete with other alpine herbivores like ptarmigan or even livestock. Marmots may also act as vectors for diseases such as the plague. Here to discuss some of the potential impacts of introduced marmots on the alpine environment in Spain, is Dr. Isabel Catalan Barrio from the University of Iceland. >> The first marmot introductions to the Pyrenees were carried out with conservation and recreational purposes in mind. Initially, it was hunters and landowners who carried out these introductions. But during the 1970s and 80s, it became a regular practice of national park staff. It didn't take very long for stable populations of marmots to establish and spread over the southern side of the Pyrenees. Sunny slopes, together with the lack of natural predators or competitors, rapidly facilitated their expansion throughout, where they seem to be doing quite well. The rapid expansion is characteristic of an invasive species, but the impacts of marmots on these mountain ecosystems has not been thoroughly evaluated. In fact, marmots are generally regarded as a valuable species for promoting tourism in the Pyrenees. Marmots occupy mostly the subalpine belt, which is the area below the treeline that has been converted to grasslands by human management. So marmots utilize the same areas as grazing livestock and can interfere with agricultural practices. Because marmots dig burrows and they consume alpine vegetation, they can impact the environments in which they live. It has been suggested that marmots could alter food webs in the mountains. For example, marmots provide abundant food for some predators that could affect other declining species, such as the black grouse in the Alps and chamois and hares in the Pyrenees. Burrowing by mammals can modify hydrological properties of soils but also provides shelter for other alpine species. Mammal burrows are known to create unique micro-ecosystems, where a community of high altitude insects can survive. Mammal burrows are also used by other animals such as foxes or a temporary shelter by ptarmigan, toads, and snakes. >> The yak is a long haired bovid found throughout the Himalayan region of South Central Asia, including the Tibetan plateau. Yak have many adaptations for coping with challenges of extreme cold, low oxygen, high solar radiation, uneven terrain, and short growing seasons. Yak do best when the annual mean temperature is below 5 degrees Celsius, and the average in the hottest month doesn't exceed 13 degrees Celsius. Yak cope with cold mostly by conserving heat. This is accomplished with a thick fleece of coarse outer hair and an undercoat of fine down. Yak also accumulate a layer of subcutaneous fat prior to the winter, which helps them with heat conservation and provides an energy reserve. Their skin is relatively thick and their sweat glands are mostly nonfunctional. This is one reason why yak are intolerant of high, ambient temperature. Adaptations to low oxygen include a large chest with 14 to 15 pairs of thoracic ribs, which is more than any other cattle, large lungs, and a large heart, relative to their overall body size. So yak are capable of breathing rapidly and take in large amounts of air. Their large rumen is also a useful adaptation for alpine grazing on a mixed diet of grasses and sedges and some shrubs. Yak can graze longer grass using their tongues, but they can also graze very short vegetation by using their incisor teeth and lips. Domesticated yaks have been kept by mountain people for thousands of years for their meat, milk, fiber, and as beasts of burden for transportation across mountain passes. Their dried droppings are also an important fuel for heat and cooking, especially above the tree line. Birds have a considerable advantage over mammals, including humans, at high altitudes. In particular, birds are well adapted for efficient oxygen diffusion. The surface area of their lungs is almost ten times greater than in humans. And the barrier between the lung and the capillaries is two to eight times thinner, leading to greater diffusion of oxygen. In humans, air travels into the lungs and then out of the lungs. However in birds, air travels in one direction through the lung opposite to the blood flow in the surrounding capillaries. This unidirectional flow means that the air has a high concentration of oxygen that diffuses more readily. Birds also have another advantage over mammals in their ability to migrate over long distances. For example, bar-headed geese are common birds native to South Central Asia. Every fall, these geese migrate from their breeding grounds in Mongolia to India, returning again in the spring. This journey takes them across the Tibetan Plateau and over the Himalayas, a mountain range that contains the highest peaks in the world. Trekkers and climbers have often provided anecdotes of their observations of bar-headed geese at altitude in this region, such as that recounted by Lawrence Swan. >> On one cold and still night in early April, I stood beside the Barun Glacier near Mount Makalu, the fifth highest mountain in the world at 8,463 meters above sea level. Then, as if from the stars above me, I heard the honking of bar-headed geese. I felt I had witnessed the most incredible feat of bird flight. While I breathed heavily with every exertion and where talking while walking is seldom successful, I had witnessed birds flying more than two miles above me and they were calling. >> However, flying is the most costly and exhausting form of locomotion. So to be able to migrate for over 1,000 kilometers at an altitude that averages over 4,500 meters, bar-headed geese have developed specialized physiology allowing them to complete this journey. Compared with other geese, bar-headed geese have lungs that are 25% bigger, meaning that the volume of oxygen inhaled with each breath is larger. During high intensity flight, they preferentially breathe deeper instead of faster, which reduces dead space ventilation and maximizes oxygen diffusion in the lung. As well, the haemoglobin of bar-headed geese has a high affinity for oxygen. This means that they can transport more oxygen in the blood. In addition, they have more capillaries in their heart and muscles. This means that the diffusion of oxygen at the tissue is higher, helping these geese fly at these extreme altitudes. Dr. Bill Milsom is a zoologist at the University of British Columbia, who has been studying some of these remarkable adaptations of bar-headed geese. >> We know that birds in general have a suite of physiological adaptations that allow them to undergo powered flight. We find in the bar-headed goose now, that there are further adaptations that extend that ability and allow them to fly in very thin air where there are very low levels of oxygen. What's involved are adaptations at every step in a cascade that goes from the environment down to the mitochondria where ATP are produced. There's five steps in that chain. First of all, getting oxygen into the lung, so on the respiratory side. Then moving oxygen from the lung into the blood, from the ability of the blood to bind and transport oxygen. Then of the heart to move the oxygen from the lung to the tissues. And then adaptations at the level of the tissue for moving oxygen from the capillaries in the tissue into the mitochondria themselves. And we see adaptations at every step in that cascade in these high altitude migrants over and above what you routinely see in most other birds. Many people ask us why the bar-headed geese would migrate over the Himalaya rather than around to avoid this high altitudes. And the theory is that the birds were making those migrations long before the mountains themselves existed. So they were going from the low land feeding areas, the wetlands in India where food is abundant through the winter. To their summer breeding grounds up in Mongolia and the Tibetan Plateau, where they molt, where they grow new feathers. They can't fly, they reproduce, they have their chicks. But these are areas that are wide open, big lakes, flat areas. Can see predators coming from miles around. They're safe on the lakes. And then, when the chicks are ready in the fall, usually in October, November, they make that migration and reverse back to where the food is abundant for the winter months.