NATIVE ANIMALS
As with plant life, animal life on the Destination: Forever Ranch site is similarly diverse. The requirements animals have for survival are naturally somewhat different than for plants, but the ecological pressures they face in the form of low and sporadic rainfall and high temperatures end up affecting animals in similar ways. Desert creatures have two main ways of adapting to ecological pressures. They can adapt via behavioral modifications or they can do so in a physiological manner.
BEHAVIORAL ADAPTATIONS TO DESERTS
 |
|
Desert short-horned lizard (Phrysonoma douglassi) |
Animals that use behavioral modifications to cope with desert extremes do so via several main methods. The first one and probably the most common is to adopt the same strategy as many plants: avoid the desert at its least hospitable. This generally means avoid activity during the daytime, especially in the long waterless periods of summer. Like ephemeral plants that weather this period as seeds, many creatures, especially reptiles, amphibians, small mammals, and insects, simply reduce their activity levels to the minimum during these times. Some rodents are active all year, but only at night, whereas others enter a state known as estivation, which is a summertime equivalent of the more familiarly known hibernation. Other rodents go through a shorter daily cycle known as torpor. Torpor differs from estivation in that the former state lasts from a few hours to a few days while the latter tends to last for weeks or months on end. Cooler daytime temperatures in fall or a good soaking rainfall will bring many of these creatures out of their state of suspended animation to become active again for as long as conditions permit.
 |
 |
| An Arizona black rattlesnake (Crotalus viridis cerberus) approaches a rabbit carcass, not visible in this frame. Rattlesnakes usually kill their own prey, but have been observed scavenging dead creatures on some occasions, including this one. The Arizona black is a subspecies of the widespread Western rattlesnake |
An option available to many animals that is not open to plants is for them to migrate to better locations when desert conditions do not suit their lifestyle needs. Birds and larger mammals most commonly select this option, but occasionally insects, arthropods, reptiles, and amphibians do so as well. Obviously, some creatures are much more mobile than others. Rattlesnake migration may amount to a few miles from winter denning sites in rocky outcrops to nearby open terrain. Insects such as ladybugs congregate on hilltops in fall before overwintering en masse in forest litter and rock clefts and then fly many miles to disperse widely in the springtime. Large mammals such as mule deer spend part of the year in the deserts when rainfall has been good enough to encourage vegetative growth and may retreat during the hottest months of summer to cooler and better-vegetated mountain and chaparral locales. Birds are widely known as the champion migrators in terms of the length of their journeys. In season, the deserts may provide an excellent home for hundreds of bird species, with abundant food and shelter sources. This fact is partially responsible for the large variety of birds seen in desert regions. But many of these birds are only temporary visitors, passing through en route to their typical breeding locations. Some of them are here for days or a few weeks, but others time their arrival so that they breed here during favorable seasons. There are a number of birds that can truly be considered desert residents, living primarily or only here and not migrating at all, such as gila woodpeckers and roadrunners.
PHYSIOLOGICAL ADAPTATIONS
The other main way of adapting to desert life is through actual physiological methods. As noted above, torpor and estivation are behavioral methods of adaptation, but both also have a physiological component to them. In going into a state of suspended animation, animals significantly reduce their water and food requirements. A ground squirrel that is lying sleep-like underground may be using 30% to 70% less energy and water than it would be using if it were running about actively. Reptiles save even more energy -- their needs drop by as much as 90% to 95% during these inactive spells. In an environment where the margin of survival can be razor-thin, these savings in scarce water and food resources can easily make the difference.
Kangaroo rats (Dipodomys species) are widely considered to be among the most desert-adapted of all animals living there. These little guys never need to drink free water, in fact most of them don’t drink it even if it is available. Kangaroo rats live mainly on a diet of dry seeds. They are able to metabolize water out of the digestion process efficiently enough that most of their water needs are met by this process alone. Moreover, kangaroo rats also store their dry seeds in underground chambers for a period before consuming them. Since the relative humidity below ground is much higher than that of the air above, the seeds absorb some of that moisture. The rat then eats the seeds with this higher water content. The kidneys of a kangaroo rat are several times more efficient than the kidneys of humans. In fact, urine produced by kangaroo rats is more of a paste than a liquid. By being nocturnal and resting underground during the day the rats lose less moisture to the desiccated air. One final adaptation in kangaroo rats is that their nasal passages are cooler than the rest of their body. As the rat exhales, moisture from its breath condenses on the nasal cavity walls and is reabsorbed into the bloodstream. This is an impressive suite of physiological adaptations indeed, each of which contributes to the moisture level balance sheet to keep the kangaroo rats alive and well in even the most arid of deserts.
 |
|
Old shell and skeleton of a Sonoran desert tortoise (between the rocks), Gopherus agassizii, on the D:FR ridge |
One other desert creature of interest is the desert tortoise (Gopherus agassizii). There are two subspecies, the Mojave and the Sonoran desert tortoise. Tortoises are not tied to free-standing water for their lifestyles, as are most turtles to one degree or another. The thick, bony shell and heavy scales on the exposed parts of the tortoise’s body help minimize water losses. Desert tortoises are long-lived, possibly 80 to 100 years in the wild and longer in captivity, slow to reproduce, and live on a home patch of desert terrain for most of their entire lives, coming gradually to know it as well as we humans do our own back yards. Adults are usually about a foot long and 8 inches wide. They spend about 7 to 8 months a year in their burrows, which have been measured as being up to 30 feet in length. Active mainly during the warm months, desert tortoises have the ability to store up to a quart of water in their bladders, using this as a reservoir for dry periods. If handled, a desert tortoise may void this water in an effort to protect itself from the threat it perceives in its handler, and this loss may reduce its ability to survive a long dry spell. Therefore, unless the tortoise is in immediate danger (as on a roadway), people ought not pick them up just for fun. If moving one is necessary, do so quickly and while keeping the animal low to the ground and upright. Move it off the road in the same direction it was headed, or else it is likely to turn back around once you leave and re-enter the roadway again. Desert tortoises are considered endangered by human activities, including road-kills, off-road ATV and motorcycle use, illegal collection for the pet trade, harassment by domestic cats and dogs, and respiratory diseases brought on by contact with people and their pets. Please be respectful of these wonderful desert animals and let them go about their long life in the desert.
ANIMAL DIVERSITY IN DESERTS
Despite the sometimes harsh conditions prevalent in desert environments, many thousands of animal species do live here. In fact, desert regions tend to have some of the highest diversities of reptiles, especially lizards, in the world. Similarly, arid and semiarid regions also tend to have very high diversity in bees, wasps, and ants. Small rodents also diversify well in these regions. One reason for the speciation (the forming of new and distinct species) in these creatures is that, since they are not as mobile as larger animals or birds, there is a greater tendency towards genetic isolation due to climatic and geographical factors. Many reptiles living in one valley are prevented from trading genes with others in the next valley over by high and cold mountain ranges that they cannot cross. The reverse is true for mountain species that cannot survive a trek across wide, arid valleys. Over evolutionary time, populations of animals become more and more separated from one another, and hence subspecies or even full-fledged new species develop.
The number of desert animals at D:FR is fairly high given its three-way transition zone status and the diversity of habitat types available within a short radius of the Gardens. Here at D:FR, we believe in living harmoniously with all desert animals, including the poisonous ones most people don’t like or want to understand. We recognize the right of all creatures to their place in this world, and although certain control measures may need to be taken to keep rabbits from devouring the cacti as soon as they are set out, every effort will be made to keep this at a non-lethal level.
Here is a short and incomplete list of animals recorded on and near Destination: Forever Ranch and Gardens:
| Mammals | |||
|
|
|
|
| Birds | |||
|
|
|
|
| Reptiles/Amphibians | |||
|
|
|
|
| Insects/Arthropods | |||
|
|
|
|