The Wildlife of the World’s Deserts – Part 9 – The Americas Cont’d

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The Bird Lakes of the Great Basin

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Spring and autumn bring millions of migratory waterbirds to the lakes of the Great Basin. At peak times the skies are filled with flocks of waders, such as Wilson’s Phalaropes, which feed on the lakes before continuing on their journey. The Great Basin extends to little over 500,000 square kilometres, over most of the state of Nevada and over half of Utah, as well as smaller sections of three other neighbouring states. Located in the rain shadow of the Cascades and Sierra Nevada, this region is a predominantly high-altitude desert, with annual precipitation rarely amounting to more than 300 millimetres and with much of it falling as snow during the winter. Summer thunderstorms can bring heavy downpours. The climate is generally harsh, with high summer temperatures and sunshine levels high all year round.

The Great Basin isn’t one big lake but comprises many small ones. Geologists, geographers and other authorities now agree that the Mojave and Sonoran Deserts mark its southern boundary and that the Columbia River denotes its northern edge. Overall, this is a rugged landscape of isolated mountain ranges, valleys, and open plateaux, with the highest peaks topping 3,7000 metres. Evaporation is very high and although there are streams leading through this forbidding terrain, none ever reach the ocean. However, there are permanent water features in the Great Basin Desert and some of these are vast. The Great Salt Lake is the largest salt lake in the Western Hemisphere and the most important water feature in the Great Basin. With no outlets to the sea, the lake is highly saline, and it has no permanent fish population. However, what the lake is noted for is phenomenal blooms of brine shrimps and brine flies that attract vast numbers of birds,  and it is an oasis in an otherwise extremely arid area.  The lake is one of the most important sites on the Pacific Flyway, the avian migration path that extends from Alaska to Mexico, and beyond.

The lake is particularly valuable to migratory waterbirds, with an estimated six million birds using it. These include half a million Wilson’s Phalaropes, also red-necked Phalaropes, American Avocets, Black-necked Stilts, California Gulls, and White Pelicans. During May and June, and again in September and October, the mixed congregation of birds makes for an unforgettable spectacle.

The female Wilson Phalaropes have more brightly coloured plumage than males during the spring. They pursue the males and defend territory, but once their eggs are laid they migrate, leaving the males to rear the young.

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Gunnison Island in the Great Salt Lake has an important colony of American White Pelicans, with several thousand birds nesting there each spring. Pelicans are very sensitive to disturbance and whole colonies will abandon their eggs and young when disturbed.

Other important wetlands in the Great Basin include Franklin Lake, Ruby Lake, and Pyramid Lake, a few kilometres apart from each other in neighbouring Nevada. Pyramide Lake is so-called thanks to the distinctive pyramid-shaped tufa formations. The lake is home to several rare fish, including the endemic Cui-ui Lakesucker as well as breeding pelicans and a variety of wintering waterfowl.

Together these lakes are major hotspots for birds regionally. The extensive wetlands are in excellent condition and attract a range of resident, breeding and migratory birds. Nesting species include the White-faced Ibis, Trumpeter Swan, and several types of wildfowl. By the early twentieth century, the largest swan in the world, the Trumpeter Swan, had been almost wiped out through hunting, except in Alaska and Canada. Reintroduction schemes have since helped to boost the population.

Although much of the Great Basin is privately owned, many areas are protected by government decree. Among these is the Great Basin National Park, established in 1987, which includes the Lehmann Caves National Monument, a protected site since the 1920s. Located in the far east of Nevada, the park covers a wide variety of terrain from valley floors to the 3,982 metres high Wheeler Peak. It has a diverse range of vegetation, from sagebrush plains and saltbush, to pinyon pine and juniper woodland, including the finest groups of Great Basin Bristlecone Pines.

The three species of Bristlecone Pine are endemic to the United States and are considered by scientists to be the oldest living single organisms, with the most mature specimens of Bristlecone Pine thought to be close to 5,000 years old and found in California’s White Mountains; this means they are older than the pyramids of Egypt. Their rate of growth is extremely slow, even the oldest of trees rarely reaches more than 17 metres in height, although their girth can exceed 10 metres. Hardly any other tree species can withstand the harsh conditions of this environment and so not having competition, the pines often form dense stands. Bristlecone Pines are so-called because of the long, hooked spine that grows on the scales of the cones. Before developing into mature cones, the bright flowers bring rare colour to the trees. Reproduction rates are very slow, which is one reason why the numbers of Bristlecone Pines are dwindling.

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Owens Valley in California is situated on the western edge of the Great Basin. The sagebrush vegetation typical of this area is home to mammals such as Pronghorn Antelope, Black-tailed Jackrabbit, Desert Cottontail, ground squirrel, Kit Fox, Coyote, and other smaller creatures. With outsized ears, the Black-tailed Jackrabbit is very distinctive. His huge ears ensure extremely good hearing and also act as a cooling system. Heated blood circulates through the thin ear tissue and cools as it does so.

Kit Foxes are arid zone specialists and the smallest members of the fox family in North America. They are mainly nocturnal and their diet varied: it includes fruit, flowers, rodents, rabbits, reptiles, and birds. In spring, females give birth to up to six or seven pups. Like all youngsters, they are very cute.

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The mountainous parts of the Great Basin National Park are home to both Puma, known locally as Cougar or Mountain Lion, and Bobcat. Pumas are well equipped to cope with cold weather and remain active under all conditions. They hunt singly, often killing animals larger than themselves. They prey largely on the Mule Deer that are abundant here, but will also take Bighorn Sheep. Other predators include the resident Golden Eagle and the iconic Bald Eagle, a common visitor in winter. Winters in the Great Basin are harsh and long. Temperatures can remain well below freezing for weeks and snow is often deep. Wildlife can be hard to find at such times but 70 percent of North America’s mammal species have been recorded here.

The Chihuahuan Desert

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North America’s second-largest desert, after the Great Basin, is the Chihuahuan Desert. It covers 360,000 square kilometres of the southwestern United States and Northern Mexico, straddling two countries and several separate states. The northern part is divided by the Rio Grande and to the western side, it crosses to the warmer Sonoran Desert. Its central and southern sections are flanked by the Sierra Madre Oriental. Much of the desert sits on a plateau between 600 and 1,500 metres above sea level. The desert is covered by a series of shallow basins, carpeted by grassland, cactus savannas, and scrub-dotted plains, as well as extraordinary expanses of gypsum dunes, the so-called White Sands of the Tularosa Basin in New Mexico. The Rio Grande forms the boundary between the United States and Mexico, and the permanent presence of water provides a habitat for fish and bird populations.

Rocky outcrops and mountain ranges provide diversity and a dramatic effect on the scenery. A series of isolated upland formations – the so-called ‘sky islands’ – rising from the desert floor are among the most important sites in the whole of the Americas. Big Bend National Park in Texas is the largest protected area of the Chihuahuan Desert and home to some of the cacti that are characteristic of this ecosystem. These include many species of Agave, which were traditionally used for medicine by local people.

The altitude of the Chihuahuan Desert means that winters are more severe than those in the Sonoran Desert, with frost common in the north and temperatures falling well below freezing. Rainfall varies across the desert but rarely amounts to more than 250 millilitres per annum. A superb display of wildflowers follows the rain, although the magnitude of this spectacle is closely linked to annual precipitation. There are over twenty species of Cholla cacti, which are characterized by cylindrical stems and segmented joints. They vary greatly in height from just 20 centimetres to as much as 3 metres. Most species bloom from April to June.

The Chihuahuan Desert is well known for its succulents and cacti, with over 400 species recorded here. Cacti such as Opuntia are especially common and widespread, as are several types of yucca. These include the Soaptree Yucca, one of many desert plant species that traditionally provided the local native Americans with virtually everything they needed. Soaptree leaves and fibre were used to make mats, baskets, clothing, and footwear, and the trunk and roots were ground to yield a substance traditionally used as soap and shampoo.

An interesting example of natural plant intelligence is the Creosote Bush, which is able to survive the scantiest and most unforgiving of soils, thanks to a complex root system that extends both radially, just below the ground surface, and downwards, enabling it to reach water reserves that are out of reach to some other plants. It also appears to be able to regulate its population density, so that each plant can obtain adequate moisture. In a particularly dry location, Creosote Bushes grow in a discernibly grid-like pattern with almost equal distances between each plant. This is in response to the reduced availability of water, with each bush needing a certain amount of space around them. Remarkably, seedlings that attempt to grow in the gaps between the plants are killed off by a toxin released through the roots of the more established bushes around them.  A fine example of an evolutionary adaptation that ensures plant survival.

Located at the northern end of the Chihuahuan Desert, the White Sands National Monument is the largest gypsum dune field in the world. The dunes are very active, with some moving more than 9 meters in a year.

Another characteristic species of the Chihuahuan Desert is the Mesquite, a type of deciduous shrub or small tree which can reach heights of 7 metres or more and is one of the largest desert plants.  A member of the pea family, its size and large number of leaves mean that it suffers a high level of water loss but this is counteracted by the fact that the Mesquite has some of the longest known roots of any plant.  Mature specimens can have roots over 20 metres long and the plant can regenerate from points up to 15 centimetres below ground level, which helps it survive both flash floods and fires. It reproduces through beans in its distinctive seedpods, which are an important source of nutrition for many species of desert mammal. The Coyote is especially partial to Mesquite beans and in late summer these may form up to three-quarters of its diet in the desert. Coyotes are wildly distributed across North America and Central America.

Coyote are hugely opportunistic and very skillful hunters; they can live in packs, pairs or alone, hunting both by day and night. They eat without fuss anything going, be it fruit or discarded hamburgers in the car park, or small mammals, birds, reptiles, but with rodents being the largest component of their diet. The howling and distinctive ‘yipping’ cries of coyotes are a regular and atmospheric sound of the night in the desert. They live in dens which they excavate themselves.

Bobcats are a type of lynx and are found across North America in a range of habitats, including semi-desert. Although relatively common, they are highly elusive and rarely seen. Their usual prey is rabbits, but they will also take insects, birds or even a small deer.

Other desert-dwelling mammals are Collared Peccary, usually found in groups of anything between six and fifty individuals. This species of the wild pig has razor-sharp tusks used by males to defend themselves against would-be predators, and in competition with other males for females in their harem. Peccaries are usually found in Mesquite scrub and they feed on agave and prickly pears. They are preyed on by humans, Coyotes, Bobcats, Pumas, and the most spectacular of them all – the Jaguar.

The most powerful cat, the Jaguar was once wildly distributed across northern Mexico and the southwestern United States, but the resident US population was hunted to regional extinction in the early twentieth century. In recent decades, they appear to be gradually recolonising from the south. Although it is an encouraging sign, pressure remains as several Jaguars have been killed in road accidents and by farmers worried about their stock. Jaguars are not classic desert animals, as they prefer as their habitat a thick forest or well-wooded wetlands but they are able to use the desert network of canyons and watercourses as they are excellent swimmers. Slowly they are beginning to restore their numbers in the northern part of the desert.

The Desert Bighorn Sheep is another animal recovering from near extinction. Once widely distributed across the American desert regions in scattered herds on mountains, rocky outcrops and in the foothills, the Bighorn was a prize target for trophy sportsmen, and uncontrolled hunting drove many local populations to extinction.  Bighorns are ideally suited to rocky terrain and move with utmost ease over the most rugged of landscapes. The males are particularly impressive, especially during the annual rut, when the crash made by colliding horns of two sparring males echoes around the mountains. Wary of people, bighorns move away at the first sign of humans, the most common view being of their distinctive white rumps as they scramble over the horizon out of sight. Reintroduction programmes are slowly returning this magnificent animal to parts of the desert, with the focus of much conservation attention being on the provision and maintenance of adequate sources of water – bighorn sheep need to drink at least every two or three days.

Water management is just one of many pressing conservation issues in the Chihuahuan Desert. Overgrazing, with ranching, is very much part of the land use pattern here. The overexploitation of certain desert plants, such as Mesquite, which is harvested for charcoal production, can have an undesirable effect on the fragile desert environment, as can the mining of minerals such as gypsum. As in many deserts around the world, human intervention brings problems and disturbs wildlife.

The wild horses of the desert are on the way to extinction, as they are rounded up by helicopters, held in pens and then sold to farmers.

 

 

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