NATURAL AND SCIENCE
The nearly 800,000 acres of Joshua Tree National Park were set aside to protect the unique assembly of natural resources brought together by the junction of three of California’s ecosystems. The Colorado Desert, a western extension of the vast Sonoran Desert, occupies the southern and eastern parts of the park. It is characterized by stands of spike-like ocotillo plants and “jumping” cholla cactus.
The southern boundary of the Mojave Desert reaches across the northern part of the park. It is thhe habitat of the park’s namesake: the Joshua tree. Extensive stands of this peculiar looking plant are found in the western half of the park.
A third ecosystem is located in the western most part of the park above 4000 feet. The Little San Bernardino Mountains provide habitat for a community of California juniper and pinyon pine.
The plant diversity of these three ecosystems is matched by the animal diversity, including healthy herds of desert bighorn and six species of rattlesnakes. Joshua Tree Naational Park lies astride the Pacific flyway of migratory birds, and is a rest stop for many. It was for this unusual diversity of plants and animals that Joshua Tree National Monument was set aside on August 10, 1936.
The park also en
The broad vistas of desert landscapes can distract the visitor’s eyes from the small and quick near at hand. Despite the impression that the desert is lifeless, many animals make their homes in deserts. Birds, lizards, and ground squirrels are most likely to be seen because they are largely active during the day. However, it is at night that desert animals come out to roam. Mostly nocturnal animals innclude: snakes, bighorn sheep, kangaroo rats, coyotes, and black-tailed jack rabbits. Dusk and dawn are good times for viewing many kinds of animals, both those just going to bed and those just getting up.
Animals that thrive in desert environments often have special adaptations for dealing with limited water and high summer temperatures. One does not walk far in the desert without seeing a multitude of burrow openings. The smaller mammals and all reptiles take refuge from the heat underground. Reptiles ar
Most of the reptiles and many small rodents and insects go into an inactive state of hibernation during the winter. However, winter is the time of greatest bird concentrations in the park, because of the presence of many migrant species.
Frogs are probably the last thing that people expect to see when they visit the desert. However, some frogs and toads have adapted to life in arid lands. True, they still need water, but they seek it out when it is available. Amphibians are animals that have two life stages: a larval, aquatic form and an adult, terrestrial form. This is the difference between a tadpole and a toad. In Joshua Tree, we have two important amphibians. The California tree frog is found only in southern California and is listed as a Species of Special Concern. It is found in the rocky, permanent water sources created by the Pinto Fa
You can find insects, spiders, and other multi-legged creatures (arthropods) anywhere in the world. So it is no surprise that there are thousands of species of arthropods in Joshua Tree National Park. They range in size from the four-inch-long tarantula (Aphonopelma iodium) and the green darner (Anax junius)—with its four-inch wingspread—to tiny gnats and mites. Joshua Tree’s arthropods include the beautiful salmon-colored fairy shrimp (Branchinecta), the fi
To alert the female of his presence, the male taps one of his legs against the ground until the female emerges. The male must then participate in a dangerous mating dance, wherein he fends off the female, who wishes to devour him, by using hooks on his front legs. His death will give the female a needed boost of nutrition, as she must now produce 500 to 1,000 eggs and a silk cocoon where the eggs will be protected. Even if the male escapes being eaten by the female, he will still die within a few months. Females, on the other hand, often produce eggs for 25 years or more.
When not involved in the ritual of reproduction, tarantulas typically do not eat each other. Insects like beetles and grasshoppers make up a good portion of the tarantula diet, and tarantulas in the desert may also devour small lizards, mice, and even scorpions. Although tarantulas have the ability to spin silk, they chase down their prey rather than snaring it in webs. Their eight closely set eyes are not useful in hunting. Instead, thousands of sensitive hairs on the spider’s body allow it to detect subtle movements in its immediate environment and “hone in” on a victim. The tarantula strikes with its fangs, injecting venom. There is a struggle while the venom takes effect, and the tarantula must grasp its prey with the palps, two arm-like appendages between the mouth and legs. If successful, the tarantula wads up its semi-paralyzed victim, secretes digestive juices onto it, and sucks up the liquefied prey. One creature’s death leads to another’s survival; the pattern of life in the desert continues.
If you encounter a tarantula, take time to observe its body, its behavior, and its connection to the fabric of desert life, but please do not disturb this delicate connection. Wildlife should never be touched, chased, or fed, and the tarantula is no exception. Contrary to appearance and reputation, the tarantula is a timid creature and will not bite human beings unless seriously provoked. Like all animals in Joshua Tree National Park, the desert tarantula deserves our respect, not just for surviving, but for thriving in a place where the boundary between life and death is always shifting.
With over 250 kinds of birds recorded from Joshua Tree National Park, it is understandable that the park affords a rewarding place to study them. This is especially true during the winter months when migrants abound. The vast majority of our recorded bird species are migrants and vagrants. Lying astride the inland portion of the Pacific flyway, the park serves as a rest stop for many migrants. The aquatic areas of Barker Dam and the Desert Queen Ranch attract many types of waterfowl on their way to the Salton Sea, birds that would not otherwise be seen in the desert. Rest stops are important for most migratory birds for purposes of water intake and for metabolism of fat reserves, which may not keep pace with energy use while they are actually in flight. Many of our migrants are actually residents of the nearby mountains, from which they fly to escape the heavy winter snows. Although most birds require drinking water almost every day, this is not such a limiting factor as might be supposed. There are many springs and seeps in the park, which are readily accessible to animals that can fly to them. The chief limiting factor for birds in the desert is food. Birds require relatively large amounts of food daily, especially during the breeding season. Thus, it is understandable that there are only 78 species of birds known to nest and raise young in the park. The park is an attractive place to sight and watch birds. The lack of dense vegetation makes birds much easier to see here than in most national parks. Golden eagles hunt in the park regularly. The roadrunner, of cartoon fame, is an easily recognized resident. And the call of Gambel’s quail is a noteworthy sound of the desert.
Joshua Tree’s resident bird species, such as greater roadrunner, phainopepla, mockingbird, verdin, cactus wren, rock wren, mourning dove, Le Conte’s thrasher, and Gambel’s quail can be sighted in the park throughout the year. The park’s winter migrants: white-crowned sparrow, dark-eyed junco, sage sparrow, cedar waxwing, American robin, and hermit thrush will remain in the park into March. Along about the time the winter migratory species are departing, other species will begin to migrate into the area for spring and summer. This group includes summer nesting species such as Bendire’s thrasher, ash-throated flycatcher, western kingbird, Scott’s oriole, northern oriole, and western bluebird.
A brightly colored bunch of warblers: Wilson’s, black-throated gray, Nashville, Mac Gillivray’s, yellow, yellow-rumped (a species also here in winter), and orange-crowned are among the species that just pass through the park. Other transients are black-headed grosbeaks, western tanagers, indigo buntings, and lazuli buntings. In addition to these smaller migrants, the park hosts a migration of birds of prey: sharp-shinned hawk, rough-legged hawk, northern harrier, osprey and Swainson’s hawk. There are several resident hawks as well: red-tailed hawk, American kestrel, Cooper’s hawk, and prairie falcon.
Occasionally groups of 200 or more turkey vultures will spend the night in the trees at the Oasis of Mara during their spring migration. They present quite a sight especially with their wings slightly spread, warming in the early morning sun. An occasional shore bird also finds its way into Joshua Tree during spring. Do not be too surprised if you see a black-necked stilt or an eared grebe standing on a park road. Grebes have their feet placed so far to the back of their bodies they cannot make a running takeoff on land—once grounded, they are stranded. Please report any sightings to park personnel so the stranded bird can be transported safely to a water site.
Fan palm oases, and water impoundments are good places to search for birds. Even “lakes” that are dry, such as Barker Dam, offer forage vegetation for birds. The Oasis of Mara, including the 29 Palms Inn at the west end, is a good bird viewing area. Cottonwood Spring has both cottonwood trees and fan palms to provide vegetation and shelter for a number of birds. Lost Palms Oasis, 49 Palms Oasis, and the riparian habitat associated with Smith Water Canyon require more extensive hiking but provide good birding as well. When in the high desert areas of the park take a walk or two in the Queen and Lost Horse valleys and look for ladder-backed woodpecker, red-tailed hawk, oak titmouse, bushtit, black-tailed and blue-gray gnatcatchers, black-throated sparrow, and sage sparrow.
Interested visitors can stop at a visitor center and pick up a bird checklist that will indicate the likelihood of a particular species being observed during each season. Also ask about any interesting bird sightings or report any unusual sightings you might make. Enjoy your park and its birds.
The chief obstacles to survival in the desert are lack of water, shortage of food, and extreme temperatures. Mammals, including humans have the ability to maintain a constant body temperature regardless of external conditions. This has advantages and disadvantages in the desert. Mammals can endure a large range of air temperatures, but are unable to tolerate even a small change in body temperature without encountering problems.
When most mammals get hot they perspire, and the evaporation of this water cools them down and helps maintain a constant body temperature. Some mammals use panting to produce the same effect. Both methods work well, but they have an important drawback for life in the desert. They involve substantial loss of water. Where water is in short supply, animals must minimize water loss. Thus, few desert mammals use perspiration or panting as their main method of keeping cool.
Because scarcity of food in the desert limits the number of large mammals that can be supported, most desert mammals are small. Joshua Tree National Park is home to 52 species of mammals. Of these, 24 are small rodents. Being small has its advantages and disadvantages. Rodents can burrow into the ground or hide in rocky crevices to avoid the mid-day heat. But their small body size means that they can gain or lose body heat rapidly. Many of them plug the entrance to their burrows to keep out the hot, desiccating air.
Most small mammals make the most of the positive side of being small, spending the day in burrows and emerging at night when the temperature drops to a more comfortable level. The larger mammals, such as mule deer and mountain sheep stay close enough to springs to be able to drink daily.
A few desert mammals, such as the round-tailed ground squirrel, a diurnal rodent, enter a state of aestivation when the days become too hot and the vegetation too dry. They sleep away the hottest part of the summer. They also hibernate in winter to avoid the cold.
Many of our Joshua Tree mammals are paler in color than their relatives in more moderate environments. Pale colors not only ensure that the animal will absorb less heat from the environment, but help make it less conspicuous to predators in the bright, pallid landscape.
Most desert mammals are herbivores and derive water directly from the plants they eat. Some, like kangaroo rats, have extreme adaptations enabling them to live without ever drinking water. They have super efficient kidneys that extract most of the water from their urine and return it to the blood. And much of the water that would be lost in breathing is recaptured in the nasal cavities by specialized organs. If that weren’t enough, kangaroo rats actually manufacture water metabolically from the digestion of dry seeds
Reptiles are closely associated with the desert in many peoples minds. This seems to be based partly on reality and partly on perception. Reptiles do form a very conspicuous part of the vertebrate fauna of warm deserts such as are found in Joshua Tree National Park. There may not be any larger number of reptiles in the desert than in neighboring less arid areas, but the lack of dense vegetation on the desert certainly makes them easier to see. Many of the lizards are especially conspicuous as they bask atop boulders or other elevated sites. Reptiles are better adapted to life in arid lands than are most birds and mammals. Being ectotherms (obtaining their body heat solely from the external environment), reptiles have a much lower cost of living than do birds and mammals which produce their own body heat using a great deal of food in the metabolic process. In desert lands, where primary productivity (plant growth) is low, reptiles are thus able to maintain larger populations on the limited food supplies than is possible for birds and mammals. The most limiting factor for life on the desert is drinking water. Reptiles are pre-adapted to such arid conditions. They do not need water for cooling because they do not perspire or pant. They just crawl into a cool hole in the heat of the day. Their scales also greatly retard water loss through the skin. In addition, reptiles do not need water for excretion; they produce no urine. Their nitrogenous wastes are excreted as a solid: uric acid. Reptiles can get all the water they need from the food they eat. Although desert tortoises and probably most other reptiles will drink water when it appears after summer rains, many lizards and snakes probably go their whole lives without a drink of water. The reptiles of Joshua Tree National Park include one tortoise, 18 lizards, and 25 varieties of snakes
With 700 species of vascular plants, Joshua Tree is renowned for its plant diversity. No wonder that when the area was first proposed for preservation in the early 1930s, the name suggested was Desert Plants National Park.
Plant communities, or what we call “associations,” describe groupings of various plant species, and are often dependent upon latitude, soil characteristics, and elevation. Using these descriptions makes it easier to understand why certain plants only grow in certain places; it also helps to identify plants in unfamiliar terrain. Plant associations within the park are divided into tree-dominated, shrub-dominated, herbaceous-dominated, and sparse/non-vegetated. Each association is named after the most conspicuous plant in the landscape.
Tree-dominated plant associations in the park include: California juniper, singleleaf pinyon, Joshua tree, desert willow, California fan palm, blue palo verde, smoketree, Gooding willow, Freemont cottonwood, and mesquite.
Shrub-dominated associations are the most diverse group, numbering 35. California Mormon tea, creosote bush, creosote bush/white bursage, blackbrush, brittlebush, bigberry manzanita, cheesebush, Mojave yucca, teddy-bear cholla, and desert almond are just a few examples.
Herbaceous-dominated associations are those communities that are mostly comprised of species like perennial bunch grasses or annual grasslands. The main associations are big galleta grass and cheatgrass.
Sparse associations include non-vegetated areas (e.g. desert pavement, rock outcrops, dunes, playas, washes, and disturbed areas) and areas with less than two percent shrub cover. These areas may be dominated by annual wildflowers during moist years, but normally appear devoid of vegetation.
Except for the occasional spectacular wildflower bloom, the desert appears to the casual visitor as an unchanging landscape. In reality it is a dynamic, constantly shifting ecosystem. Wind and rain have had the greatest effect in shaping this ecosystem. If global warming is occurring, the desert may get more rain.
Geologic processes are continually at work as well, but are so slow that we only notice their presence in the occasional earthquake. While Wildfire and human caused factors such as air pollution and off-road vehicle use can change the landscape very quickly.
The park is a “living laboratory” that helps us understand how environmental factors have shaped this desert ecosystem and how they may be changing it at present. It also shows the sharp contrast between a less-disturbed ecosystem and the completely human-shaped one in the urban areas nearby.
Park staff carefully monitor the effects of changes in air quality, and the effects of nitrogen deposition, wildfires, and invasion by nonnative plant species. Their watchful eyes can alert managers and the public to threats to desert resources in time for useful action.