Life Zones
ZONES
The 6,000-foot elevation difference accounts for three different life zones at the South
Rim: Lower Sonoran, Upper Sonoran, and Transition. These categories were invented in the
1800s by naturalist C. Hart Merriam, who noted that elevation changes within a single
region allowed a range of wildlife to live there that would normally be found only by
traversing the United States from Mexico (lowest) to Canada (highest). Although
naturalists today also include overlapping zones (called ecotones), as well as other
environmental variables in their observations, life zones are still our best tool for
categorizing wildlife.
THE RIM
The 7,000- to 7,400-foot canyon rim supports flora and fauna of the Transition Zone (7,000-8,250 feet), as well as the Upper Sonoran Zone (3,500-7,000 feet).
Trees
A dense pygmy forest of piņon pine (Pinus edulis) and Utah juniper
(Juniperus osteosperma) trees, interspersed with shrubby cliff rose (Cowania
mexicana), and sagebrush (Artemisia tridentata), is found at about 6,500
feet. Poor soil and inadequate rainfall account for their slow, stunted growth but long
lives. The piņon is scrubby in appearance and produces tasty pine nuts that have been
popular since prehistoric times, when the Ancestral Puebloans (Anasazi) relied on them for
food and trade. The piņon begins bearing cones after 25 years, and seeds after 75 years.
A bumper crop of nuts is produced approximately every seven years. Distinguished by its
waxy leaves and shaggy bark, which help the tree retain precious moisture, the Utah
juniper's bonsai-like, rustic appearance creates a dramatic silhouette against a crisp,
blue canyon sky. The juniper berries are used for medicinal purposes by Native Americans
and provide the basis for gin.
A slight gain in elevation and rainfall allows swaying ponderosa pine (Pinus ponderosa) to grow among the piņon-juniper association, along with Gambel oak (Quercus gambelii). Ponderosa pines grow best in drainage areas where soil and water are most plentiful. Sniff the bark of an older ponderosa and then debate whether the scent is closest to vanilla, caramel, or cinnamon! Distinctive Gambel oak likes warm exposures and may often be found sheltering in the lee of a ponderosa. As a young tree, it is sometimes mistaken for shrubbery, but it will grow to 20 feet. The leaves turn a shimmering russet color in fall, providing an eyeful of late color at the South Rim.
Flowering
Plants
A host of wildflowers erupts beside roads along the rim between summer and fall, when
warm temperatures arrive. Commonly seen are baby white asters (Aster arenosus),
yellow sunflowers (Helianthuas annuus), golden western wallflowers (Erysimum
capitatum), orange globemallow (Sphaeralcea parvifolia), and rabbitbrush
(Chrysothamnus nauseosus). Woodlands are awash in orange-red Indian paintbrush
(Castilleja linariaefolia) and purple hill lupine (Lupinus hillii),
with the occasional paddle-shaped plains prickly pear cactus (Opuntia
polyacantha).
Mammals
On the South Rim, you'll encounter the engaging, vocal Abert squirrel (Sciurus
aberti). This squirrel is large (about 20 inches long, including tail) and
tassel-eared, with a tail that is gray with white underneath. Do not attempt to feed
squirrels, which are known rabies carriers. It is much healthier for squirrels to eat
their evolved diets of ponderosa pine seeds, inner tree bark, and summer mushrooms.
The mule deer (Odocoileus hemionus) gets its common name from its long ears. You may catch a glimpse of this deer early in the morning or at sunset feasting on shrubs and grasses among the trees in the Village. Its hoof marks and scat are also often apparent on the slopes below the canyon rim. Should you encounter a mule deer, keep your distance! It appears tame, but it is a wild animal with sharp hooves and antlers and will defend itself when it feels threatened.
The attractive silver-gray coyote (Canis latrans), the song dog of the West and trickster of Navajo myth, moves in family packs around several life zones looking for food. A predator of field mice and squirrels, the coyote can be easily conditioned to eat food offered by people. This is harmful to the animal and makes it bolder when approaching humans.
Birds
Ten types of hawks and eagles have been seen in the park, but the one most visible is
the red-tailed hawk (Buteo jamaicensis), which patrols the airways, buoyed
along by air currents. The red-tailed hawk resides in all parts of the Canyon, except near
marshes or open water.
The cliffs of the Grand Canyon are home to the magnificent golden eagle (Aquila chrysaetos), a powerful predator that feeds on a variety of mammals. With a wingspan of up to six feet, the golden eagle can easily carry away infant bighorn sheep, as well as most rodents.
Often seen, too, is the raven (Corvus corax), a bird as common in the Southwest as it is in Native American mythology. The raven's hoarse caw and its displays of aerobatics are most noticeable around the rim. The piņon-juniper forest is the home of another bird: the piņon jay (Gymnorhinus cyanocephalus). This noisy, blue-gray bird feasts on piņon (pine) nuts every fall.
One of Grand Canyon's rarest birds is returning after a long absence. In late 1996, six California condors were released at Vermilion Cliffs, about 30 miles north of the Canyon. Less than 200 California condors are alive today. They are North America's largest land bird and have a wingspan of nearly 10 feet.
INNER CANYON
The area between the rim and the sweeping expanse of the Tonto Platform lies within the Upper Sonoran Zone (3,500-7,000 feet), where increasing desert aridity allows only the hardiest of shrubs to gain a foothold. Here, though, an array of desert plants and animals may be found that have developed ways of dealing with the conditions.
Flowering
Plants
Anyone who questions the beauty of desert plant life needs only to see cliff rose
(Cowania stansburiana), fernbush (Chamaebatiaria millefolium), and mountain
mahogany (Cercocarpus montanus) in bloom. The first two shrubs are actually
members of the rose family. The cliff rose's gnarled branches yield creamy-white flowers
early in the year, while the fernbush is a late bloomer, waiting until August to blossom.
Mountain mahogany sprouts leathery leaves and a white plume flower that twists like a
corkscrew when it rains. Delicate red Utah penstemon (Penstemon utahensis)
is found among the rocks, as are rouge carmine thistles (Cirsium rothrockii),
members of the sunflower family.
Although some cacti grow on the rim, they are more commonly found lower down the Canyon, where they flower in spring and bear vividly colored fruit in late summer. Native Americans have traditionally used some of these fruits to make sweet treats such as jams and syrups. Engelmann's prickly pear (Opuntia phaeacantha), beavertail cactus (Opuntia basilaris), grizzly bear cactus (Opuntia erinacea), and whipple cholla (Opuntia whipplei) are found on the Tonto Platform and below.
Mammals
Desert bighorn sheep (Ovis canadensis) are shy, sure-footed creatures
that are able to move at will around the seemingly inaccessible ledges and outcroppings of
the Canyon between river and rim. They pick among the cracks in the rock in search of
forage that prospers in soil pockets. Formidable and stately horns identify this
mountaineer, which, after near-extinction, is gradually being reintroduced throughout
western deserts.
Reptiles
Well suited to the warm inner canyon, reptiles are often encountered basking in the
sun early in the morning, before the heat becomes too intense and they must shelter to
regulate temperature. During the winter, when freezing temperatures may occur, Grand
Canyon species usually hibernate. Most of the snakes encountered in the Canyon are
harmless to humans. They feed on rodents, such as pocket gophers and kangaroo rats, and
insects. Poisonous snakes, such as the Grand Canyon rattlesnake (Crotalus
viridis abyssus), are found in the area but are rare. This snake has a diamond-shaped
pattern on its skin and a distinctive rattle. The colors of the Grand Canyon rattlesnake
blend well with the snake's surroundings, making it inconspicuous to its small prey and
hikers, who should walk carefully.
The many species of desert lizards living here are able to tolerate higher temperatures than snakes but are frequently unable to bear sizzling temperatures in the inner gorge. The large chuckwalla (Sauromalus obesus) is the largest and most distinctive of them. You may also come across a short-horned lizard (Phrynosoma douglassi) or a banded western collared lizard (Crotaphytus collaris).
Birds
The Grand Canyon is an outstanding bird habitat. As you descend into the canyon, you
are sure to hear the sweet, descending notes of the canyon wren (Catherpes
mexicanus) reverberating off canyon walls. This little bird's unique song is an easily
distinguished sound in our Southwestern canyons.
INNER GORGE
Below the Redwall Limestone, down at the river in the Lower Sonoran Zone (below 3,500 feet), there is an interesting contrast where desert abuts riparian environment. Here, the preternatural green of the thick growth along the beaches stands out against the dark schist of the canyon walls.
Plants
Daggerlike yucca (Yucca angustissima), whose threads were used for
sandal-making by the Ancestral Puebloans, may be found among dry rock, while thirsty
pink-tinged tamarisk (Tamarix pentandra) vies with statuesque Fremont
cottonwood (Populus fremontii) for a place on the beaches. Hanging gardens of
colorful columbines (Aquilegia chrysanta) and monkey flowers (Mimulus
cardinalis) are a delightful surprise here.
Mammals
The ringtail cat (Bassariscus astutus), a quiet nocturnal mammal that
resembles a raccoon, flourishes near the riparian habitat of the Colorado River.
Occasionally raiding campsites after dark, the ringtail is a beneficial predator that
feeds primarily on rodents, large insects (such as crickets and grasshoppers), scorpions,
carrion, reptiles, and amphibians, as well as fruits and berries.
Birds
Shady glades and creeks of the Inner Gorge are the homes of insect-eaters such as the black
phoebe (Sayornis nigricans), the yellow rumped warbler (Dendroica
coronata), and the Bell's vireo (Vireo bellii). Ducks and great blue
herons also enjoy the river.
Fish
In the colder waters emerging from Lake Powell, sport fish such as rainbow trout
(Salmo gairdneri) have thrived, threatening species such as humpback chub (Gila
cypha) and humpback sucker (Xyrauchen texanus), and wiping out the Colorado
squawfish (Ptycholcheilus lucius), all of which used to thrive in the warm
waters of the Colorado before it was dammed. These warm-water fish are now protected by
the Endangered Species Act.
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