Australia's Great Basin

The Lake Eyre Basin of east-central Australia is a vast topographic bowl within which streams drain toward the lowest part of the basin, never reaching the sea.  Covering 440,000 square miles from southwestern Queensland to South Australia and from the southeastern corner of the Northern Territory to the northwestern edge of New South Wales, most of it is dry, desert landscape through which ephemeral streams lead to Lake Eyre, in the southwest corner of the Basin.  Nearly dry and coated with salt flats most of the time, the lake fills only twice each Century (on average); composed of a large northern basin connected to a smaller southern basin by the Goyder Channel, Lake Eyre covers 3700 square miles and has an average depth of less than 10 feet (when full)  The lowest point of the lake basin, in Belt Bay of the northern portion, is 50 feet below sea level while the rim of the lake is 30 feet below the level of the sea.

The Lake Eyre Basin began to form about 200 million years ago, when Australia was part of Gondwanaland.  Tectonic forces caused the crust of this region to subside and, within another 100 million years, an arm of the sea invaded the basin; when uplift occurred along the northern and eastern margins of the basin, the sea drained away and rivers flowed across the region, depositing sediments on their way to the ocean.  During the middle of the Pleistocene, about 1 million years ago, uplift along the southern rim closed off the basin and all streams fed Lake Diers, the much larger predecessor of Lake Eyre (as Lake Bonneville preceded the Great Salt Lake in the U.S.).  As the climate became warmer and drier late in the Pleistocene and into the Holocene, the flow through the rivers diminished and eventually became sporadic.  Today, what little water reaches the lake is via three primary river systems: the Georgina River from the north, the Diamantia River from the northeast and Cooper Creek from the east.  Most streams from the west and northwest dry up before reaching Lake Eyre.

During those rare periods when monsoon rains or tropical storms fill Lake Eyre, this remote oasis attracts huge flocks of shorebirds, terns and Australian Pelicans that nest on the islands and feed in the shallows; how these birds know that the distant lake is full remains a mystery.  Lake Eyre National Park stretches along the east shore of the northern lake, just a short 435 mile drive north from Adelaide.  Major towns within the Lake Eyre Basin include Alice Springs, Mt. Isa, Longreach and Broken Hill.

High Deserts

To most of us, deserts are landscapes of dryness, sparse vegetation and perpetual heat. But, in high deserts, the interplay of elevation and dry air produces wide temperature variations from day to night and from one season to another. Examples within the U.S. include the Great Basin Desert, with floor elevations from 5000 to 6000 feet, the Red Desert of southern Wyoming, ranging from 6000 to 8500 feet, and the San Luis Valley of Colorado, with an average elevation of 7600 feet. In all of these deserts, hemmed in by mountain ranges, the annual total precipitation is below 10 inches and surface temperatures may vary by as much as 70-80 degrees F between night and day.

However, the high deserts of the U.S. pale in comparison to the extreme conditions found in other regions of our globe. The Gobi Desert of Mongolia and the varied Patagonian Desert of Argentina are somewhat comparable with regard to elevation but are far larger and are affected by the extreme conditions of neighboring ecosystems. The Atacama Desert of Peru and Chile, the driest on Earth, stretches from the sea to the foot of the Andes and thus harbors varied life zones from zero to 11,000 feet or more. Among the highest deserts in the Western Hemisphere are the Bolivian Salt Flats (12,000 feet) and the Salinas Grandes of Argentina, 12,500 feet above sea level.

But the most impressive high deserts on our planet are the Tibetan Plateau, north of the Himalayas, averaging 14,500 feet in elevation, and the Antarctic Plateau of east-central Antarctica, with a mean elevation of 9800 feet. Despite the fact that its ice and snow harbor over 70% of the fresh water on Earth, Antarctica is our driest Continent, with most of its precipitation falling along the coastal shelves; ascending toward the great plateau, the dry polar air cools further, dropping its meager cargo of moisture on lower terrain.

Musk Hogs

Collared peccaries, otherwise known as javelinas or by their more colorful title of musk hogs, are native pig-like residents of the Sonoran and Chihuahuan Deserts of the Southwest U.S., from southern Arizona to southwest Texas. They and other peccary species are also found southward through Mexico, Central American and most of South America. All are descendents of a Eurasian ancestor that split from the common pig lineage back in the Eocene, some 50 million years ago.

Living in herds of up to 50 individuals (10-20 is typical), collared peccaries roam the canyons and arroyos of the Desert Southwest, under the control of a dominant male. He breeds with females in the group throughout the year and pregnant females temporarily leave the herd to deliver their young (usually 2) in a den or hollow log. Older sisters help to raise their new siblings and newborn females are sexually mature within a year.

Thinner and longer-legged than common pigs, collared peccaries have a coarse coat of gray-brown hair with a darker mane down their back and a lighter ring around their neck; while their eyesight is rather poor, these desert residents have a keen sense of smell. Short, sharp tusks offer some protection from predators (mountain lions, coyotes, bobcats) but their aggressive nature and group mentality provide their best defence. Omnivorous, peccaries feed on a variety of plant materials (prickly pear cactus and agaves are favored) but also consume eggs, reptiles and carrion; avoiding the heat of mid-day, they usually forage in the early morning and evening hours. The name "musk hog" is derived from the potent musk gland on their upper rump which they use to mark their territory and one another.

The Desert Raccoon

Natives of Central and South America, coatimundis have spread into the Sonoran and Chihuahuan Deserts of the southwestern U.S. Formally known as white-nosed coatimundis, these members of the raccoon family, unlike their more widespread and familiar relatives, are diurnal and gregarious, often moving about in noisy bands composed of females and their young.

Adult males, twice as large as the females, weigh up to 25 pounds and tend to be more solitary. Mating occurs in the early spring and 4-6 young are born after a gestation of almost 3 months. Females often use rock crevices for nursery dens but she and her offspring later use crude arboreal platforms for sleeping and resting. Wandering about for much of the day, these omnivores locate food and prey with their long, tapered snout; insects, lizards, eggs, nuts and fruit comprise most of their diet. Coatimundis are agile climbers, equipped with sharp claws to grasp limbs and a long tail for balance.

Favoring wooded canyons of the Desert Southwest, white-nosed coatis and their brown-nosed South American cousins are threatened primarily by habitat loss. Natural predators include mountain lions, coyotes, bobcats and golden eagles in the U.S. and jaguars, ocelots and boas in Central and South America. Known to live up to 15 years in captivity, coatis have a natural life span of 6-8 years.

Kofa NWR

If you enjoy an escape to the Desert Southwest during the winter months but hope to avoid the congestion of large cities and National Parks, consider a visit to Kofa National Wildlife Refuge, northeast of Yuma, Arizona. This extensive preserve (over 665,000 acres) was set aside in 1939 to protect habitat for desert bighorn sheep; more than 80% of the refuge is designated wilderness and it thus harbors some of the most pristine Sonoran Desert landscape in the U.S.

Stretching between the Kofa Mountains on the north to the Castle Dome Mountains in the south, this refuge is accessed by a network of graveled roads, most of which require four-wheel drive vehicles. However, the road to Palm Canyon, leading east from US 95 between Quartzite and Yuma, can be traversed by the family car and is perhaps the best means to explore this ecosystem; a short trail at its terminus leads to a stand of California fan palms and conditioned hikers can proceed on to higher terrain.

In addition to the fan palms, the only palms native to Arizona, Kofa NWR is known for its tremendous diversity of Sonoran Desert plants, including the Kofa mountain barberry. Of course, the refuge is also home to a spectacular variety of desert wildlife; joining the reclusive desert bighorn sheep are mountain lions, coyotes, mule deer, kangaroo rats, five species of rattlesnake, a diverse collection of lizards and the usual mix of Sonoran desert birds. Named for the abandoned King of Arizona gold mine, this wilderness also harbors remnants of past mining and ranching activity; since it was used for military training during WWII, it may contain unexploded ordinance and visitors are cautioned not to handle such materials.

The Elusive Ringtail

The ringtail, named for its bushy, banded tail, is a small, nocturnal omnivore of the western U.S. and northern Mexico. Extremely agile, these cousins of the raccoon favor semi-arid areas with rock outcrops and open woodlands; there they hunt small mammals, birds and lizards and seasonally feast on nuts and berries. Since they are active primarily at night, ringtails are seldom encountered by hikers and campers.

Though often called ringtail cats, due to their size and behavior, they are not felines; once domesticated by miners to control rodents, they are also known as miner cats. Ringtails are solitary for most of the year but pair off in late winter or early spring to mate; the litter of kits (usually 2-4) are born in late spring and stay with their mother through summer. Dens are usually placed in small caves or rock crevices but ringtails are superb climbers and often rest in trees.

Natural predators of ringtails include hawks, owls, coyotes, fox and bobcats. Those fortunate enough to escape these hunters often live 7-8 years in the wild and have been known to live 15 years or more in captivity.

The Nature of Haboobs

Haboobs are dense, atmospheric walls of dust or sand that are encountered in arid regions across the globe. Ironically, they usually develop during the monsoon season when downdrafts from nearby thunderstorms produce outflow gust fronts that sweep particulates into the air. Moving out from the central storm, the imposing wall may be a mile or more high and closes in at 30-50 miles per hour, producing a visual doomsday effect.

Though short-lived, haboobs dramatically reduce visibility and, while they may bring destructive winds and induce breathing difficulty, their primary danger results from the rapid loss of visibility, leading to vehicular accidents. Fortunately, they can usually be spotted from a safe distance and modern radar systems provide ample warning of their development, reducing the occurrence of injuries and fatalities.

Yesterday's haboob in Phoenix, Arizona, was spawned by a cluster of thunderstorms northwest of Tucson. According to the Weather Service, this arc of dust and sand was 60 miles across, one of the more spectacular haboobs to strike the Desert Southwest in recent years.

The Desert Owl

Elf owls, the smallest owls in North America, are summer residents of the Sonoran Desert in southern Arizona; some inhabit the Chihuahuan Desert of southernmost New Mexico while others breed in dry country along the Rio Grande River of southern Texas. Less than six inches tall, these tiny raptors are best identified by their yellow eyes, white eyebrows and round, tuftless head.

Calling from a potential nest cavity in April, the male attracts his mate and both parents incubate the eggs (usually 2-4) for several weeks. Nest cavities, always more than ten feet from the ground, are abandoned woodpecker holes in saguaro cacti or in sycamores along streams near the base of mountain ranges; gila woodpeckers usually sculpt the saguaro cavities while flickers and acorn woodpeckers provide those in riparian areas. Strictly nocturnal, elf owls feed primarily on flying insects but may grab a scorpion or ground beetle; during the breeding season, they are often active at dusk but are otherwise best observed within their cavity during the daylight hours.

Relying on a diet of insects, these small owls migrate southward into Mexico for the winter, when chilly nights eliminate their prey in the Desert Southwest. Since they inhabit arid landscape with few larger owls, roost in cavities far from the ground and capture their meals in mid-air, elf owls have few natural predators and may live up to six years in the wild.

Madera Canyon

The mountain ranges of southeast Arizona offer steppingstones of forest for birds migrating between the Sierra Madres of Mexico and the Rocky Mountains of western North America. In addition, these sky islands provide cool, moist retreats for the birds and other wildife that reside in the Sonoran Desert, concentrating their populations and making them more accessible to humans who hope to observe them. Harboring a mix of Mexican and North American species, these ranges are thus renowned as superb birdwatching sites and Madera Canyon is among the more popular destinations.

Incising the northwest flank of the Santa Rita Mountains, 25 miles SSE of Tucson, Madera Creek rises along the crest of the range (an elevation of almost 9500 feet) and drops 7000 feet to the floor of the desert. Within its spectacular canyon, varied life zones attract a tremendous diversity of plant and animal life, including more than 200 species of resident and migrant birds. Among the more treasured sightings are elegant trogons, sulfur-bellied flycatchers, painted redstarts, yellow-eyed juncos, flame-colored tanagers, whiskered screech owls and 15 species of hummingbirds; the latter are best observed at feeding stations around the Santa Rita Lodge. Other canyon residents include black bears, mountain lions, bobcats, coati, ring-tailed cats, wild turkeys, black-necked garter snakes, tiger rattlesnakes and canyon tree frogs.

Accessed by a central roadway and numerous trails, Madera Canyon is a popular site for hiking and camping throughout the year; day use and camping fees are charged. Madera Creek, which sculpted this magnificent canyon, generally flows from the monsoon season of mid-late summer until depletion of the snow pack in early spring but can be dry for months at a time. Birders are advised to avoid the weekend crowds and to visit the Canyon early or late in the day.

Hominids & the Sahara Desert

The vast Sahara Desert, which stretches across North Africa, began to form in the late Miocene and early Pliocene, some 10 million years ago (MYA). South of this geophysical region, gorillas diverged from the hominid line about 9 MYA and chimpanzees followed 7 MYA. By 4.5 MYA, Australopithecus appeared in the Rift Valley of East Africa and, by 2 MYA, Homo erectus had evolved.

While the Sahara may have been a natural blockade to the northward migration of the earliest hominids, the Pleistocene Epoch (2 MYA to 10,000 YA) brought wide swings in the global climate, marked by four periods of glaciation. During these glacial periods, a cool, wet climate caused the Sahara to contract, opening corridors of savannah that likely permitted ancestral hominids to migrate northward, into Eurasia. Following earlier migrations of Homo erectus, Neandertals began to leave Africa about the time that humans were first appearing, some 150,000 years ago, and occupied Europe by 100,000 years ago. Man remained in sub-Saharan Africa until about 60,000 years ago, when the Wisconsin glaciation permitted migration through northeastern Africa and, due to lowered sea levels, directly across the Red Sea to the Arabian Peninsula.

Nomadic human tribes likely entered parts of the Sahara Desert from the earliest days or our existence but extensive exploration and settlement of that harsh landscape would not occur until the Holocene, aided by the domestication of goats (10,000 YA), sheep (9000 YA), cattle (8000 YA) and dromedary camels (4000 YA). Even today, most human settlements lie in fringe regions of the Sahara and interior towns are limited to natural oases, the Nile Valley and volcanic highlands.

Evolution of the Sonoran Desert

The Sonoran Desert of the Southwest U.S. and Northwest Mexico is a product of its latitude, the global climate and the regional topography. Lying along one of the desert bands (which run just north and just south of the Tropics), this arid ecosystem receives copious sunshine and is subjected to prolonged periods of high pressure, below which the air is sinking. This atmospheric condition retards cloud formation and both warms and dries the air as it plummets toward the Earth's surface.

Covering a broad basin and surrounded by highlands, the Sonoran Desert is shielded from moisture in all directions; to the northwest are the Sierra Nevada Mountains and the high Mojave Desert, to the north and east is the Mogollon Rim of the Colorado Plateau, to the southeast is the wall of the Sierra Madre Range and, to the southwest, are the mountains of Southern California and the Baja Peninsula. Any air that enters the Sonoran is thus downsloping from higher terrain, causing it to heat up and dry out even further. Since the mountains and plateaus that surround it were uplifted within the past 4 to 20 million years (during the Miocene and Pliocene), the Sonoran Desert is one of the youngest ecosystems on our planet.

Throughout the Pleistocene and into the Holocene, Earth's climate has undergone dramatic shifts. When the climate cooled and glaciers advanced, the area of the Sonoran Desert decreased; in contrast, when the climate warmed (as it has done over the past 10,000 years), the Desert advanced, climbing onto the walls of the adjacent highlands. Throughout these gyrations, the regional flora and fauna have evolved, developing traits that enhanced survival in an arid environment with intense sunshine, cool nights and seasonal rains.