The Wildlife of the World’s Deserts – Part 10 – The Americas Cont’d

The Atacama, the Driest Place on Earth

The coastal strip south of Chile and Peru, extending over 1,500 kilometres in total and to a width of 180 kilometres, is where the Atacama Desert forms a complex of arid lands. The extreme aridity of the region is the result of the offshore Humboldt Current, which draws cold water from the much cooler latitudes to the south. The cold water overrides the warm tropical ocean, causing a thermal and a reduction in evaporation, which means less rainfall. Instead, this creates places of intense fog, which allows the most resilient of plants and animals to survive. Actual rainfall is rare to non-existent, and when it arrives it is in the form of sudden, heavy and short downpours that do little to change the area’s decidedly lunar-looking appearance.

Part of the Atacama Desert lies slightly inland, having the mountain range of Cordillera de la Costa on one side and to the west the foothills of the Andes, which exacerbates the aridity even further by an acute rain shadow effect. Some parts of this extraordinary landscape haven’t received rainfall in hundreds of years, the ground is completely dry and barren, incapable of supporting even the most basic of vegetation. Fortunately, the cold offshore currents produce in other parts regular mists and fogs. These give just enough moisture to sustain life in the arid Atacama coastal belt. The sea here teems with life, which attracts large numbers of birds and marine mammals.

In the wider Atacama, the most biodiverse habitat occurs on the small bluffs or hills known as Lomas, on which moisture from fog collects, as well as along the few river valleys and in places where underground water is close enough to the surface to sustain plants. The nature of the Atacama landscape is dictated by the tumultuous volcanic activity that has shaped the region’s topography over many millennia. This process continues to this day, with the desert set against a spectacular and dramatic backdrop of snow-capped volcanoes, many of which are still active. Deeply incised canyons, gorges, erosional sands, and gravels predominate, as well as vast areas of salt-encrusted pans. The few watercourses that struggle through this extreme landscape almost invariably succumb to evaporation or sink into the sand, salt, and rock.

Conditions are so extreme that the Atacama vegetation is highly restricted. The Giant Cactus is a signature plant of the Atacama. When entering a grove of mature specimens, the effect is similar to being in a cathedral. The greatest number and variety of plants can be found in the ‘fog-zone’. Here shrubs and woody vegetation can grow, along with mosses and lichens. There are some 60 varieties of cacti, with most of them being endemic to the region. As with plants, the same situation exists with wildlife. Among the most unlikely is the seasonal presence of the Grey Gull, which for much of the year is a coastal-dweller, occurring along the coastline of Chile, Peru, and Ecuador. Every spring, the birds head inland to their traditional nesting sites in the Atacama, as far as 70 kilometres inland. The females each lay between one and three eggs in a simple scrape on the ground. The heat is so intense here that one of the parent birds must remain with the chicks at all times to shield them from the sun. The other parent will make the long journey to the coast, where it will feed intensively, and then return, usually after darkness – it locates its mate via call recognition – to regurgitate the partly-digested fish for the young. The next day the other parent bird will make the journey, on an alternative shift until the chicks fledge and then accompany their parents on the flight back to the coast. Grey Gulls are the slowest growing of all gull species and do not fledge until they are almost six weeks old. Much remains to be discovered about this enigmatic bird.

As far as the flamingos are concerned, the numbers of each species vary from year to year, but the overall trend appears to be downwards. Breeding success varies hugely, and evidence suggests that at certain sites the flamingos are losing out to increasingly intrusive human activity. At Salar de Punta Negra, for example, a key nesting site for the Andean Flamingos, the excessive plundering of subterranean water for a huge copper mine nearby has led to the drying up of wetlands on which the flamingos depend. As a result, thousands of Andean Flamingos abandoned their nests, with some 2,000 eggs failing to hatch. No young birds were reared. In other cases, the exceptionally hot summers may have caused salinity levels on the salt pans to rise, thereby killing off the micro-algae on which the birds feed, and they were forced to leave.

Notable land birds in the Atacama and associated arid regions include the tiny Chilean Woodstar, a species of hummingbird that can be seen only in a handful of desert valleys in northern Chile and Peru. This highly localised bird reaches a total of 7.5 centimetres and has a total population of little more than one thousand. It appears to be in decline, mainly as a result of habitat destruction as its preferred shrub is removed to make way for agriculture.

Mammals in the Atacama are few and far between, and mainly restricted to small rodents. One of these is the Mountain Viscacha, that resembles a long-tailed rabbit. It is a social animal that often lives in large colonies. In the morning they will emerge from the rock crevices and cavities in which they live and bask in the sun, before moving around in search of grazing.

The larger species of mammals include the Guanaco which is a wild relative of the alpaca and llama.  Guanaco is a flexible and adaptable species capable of thriving in a wide range of habitats, from desert grassland through to forest and at altitudes from sea level to as high as 4,000 metres or more. While most of the population is largely sedentary, those living at a higher altitude may undertake seasonal migration to avoid harsh weather.

One of the most productive areas for wildlife in the Atacama region is the Pan de Azucar National Park. Established in 1985, the park covers only a little over 400 square kilometres of dramatic coastal and inland desert but contains some of the highest levels of biodiversity in the region. Mammals that can be seen here include Guanaco, as well as Andean Fox, Chilla or South American Grey Fox, and Mountain Viscacha. Of particular interest along the shoreline is the Marine Otter, a little known species which was hunted to virtual extinction during the twentieth century for its pelt and as a result of persecution by fishermen. Numbers are now slowly recovering but this remains a scarce and elusive animal. Marine Otter is considerably smaller than the better known Sea Otter which is restricted to North America, and is less gregarious, usually moving around singly, or very occasionally, in groups of up to four. Much easier to see are South American Sea Lions, of which there is a large colony on the Pan de Azucar island offshore.

Widespread and common on both sides of the Andes, the Chilla or Grey Fox appears to be at home in a variety of habitats, from desert to thick scrub. Hunting by both day and night, it lives largely on rodents and is a frequently encountered predator.

Birdlife in the park is especially rich, particularly on the islands. Here there is an important breeding colony of Humboldt Penguins, as well as many other species such as Peruvian Pelican, Peruvian Booby, and Inca Tern. Such a concentration of sea birds is made possible by the presence of the food-rich Humboldt Current, which is probably the richest marine ecosystem in the world. However, every so often the current is disrupted by the phenomenon known as El Nino when the upwelling that is responsible for the profusion of marine creatures on which the seabirds depend stalls or even reverses. Fish stocks can subsequently plummet, and the seabirds population crashes.