During mid-summer, when daytime temperatures on Colorado's plains and arid plateaus can rise to over 100 degrees, native wildlife use a variety of mechanisms to deal with the rigors of heat and drought.
Sheltering and Nocturnal Activity
Many small mammals survive summer by sheltering from the heat of the day in deep burrows that maintain a constant temperature. The Ord's kangaroo rat is active above ground only at night. During the day, it rests in a deep, cool burrow, plugging the entrance with sand to reduce moisture loss. The kangaroo rat drinks very little free water and derives most of the moisture it needs from metabolic water produced by digestion. In fact, a kangaroo rat can subsist on a diet of dry seeds, without drinking any liquids.
Though dependent on rising ambient temperatures to warm their bodies, reptiles and amphibians can become too hot on summer days. They, too, seek cool burrows and shady 
places during hot times of day to avoid overheating. In mid-summer, for example, rattlesnakes at lower elevations rest under rocks and ledges during the day and are most active at night.
Spadefoot toads use the spadelike appendages on their legs to dig cool burrows where they shelter from hot, dry conditions. An insulating layer of dead skin helps them further reduce moisture loss. Unlike most amphibians, spadefoot toads do not require a permanent water source; they wait underground until a rainstorm triggers emergence from their burrows.
Perhaps more than any other group, fish are affected by temperature; water temperature has a direct effect on their metabolism and activities. When the sun is overhead, fish seek shady overhangs and deeper water, altering their activity cycles to cooler times of day. Cold water fishes, like trout, can't tolerate water temperatures above 75-80 degrees Fahrenheit. Warmer water holds less dissolved oxygen, favoring species like catfish and carp, which can tolerate lower oxygen concentrations.
Estivation and Daily Torpor
Though we associate hibernation with winter, some animals undergo a hot-weather version of this "deep sleep" called estivation. This state of physiological dormancy or torpor lowers the animal's need for food and water, and lessens the metabolic heat it produces. Many small desert-dwelling mammals, such as the pocket mouse, cycle through a daily period of torpor during high daytime temperatures followed by increased activity when temperatures cool in the evening. Studies indicate, however, that estivation is more a response to reduced food and water than to elevated temperature.
A daily period of torpor helps bats manage heat stress; they hang in a sheltered spot until the cool of evening, when they become active.
Loss of Heat Across Membranes
Blood vessels in bats' ears and wing membranes dilate to increase the flow of heated blood to the body surface; cooling is aided by extension and fanning of the wings. Although sweating in an arid climate can cause excessive water loss, bats achieve the same result (surface cooling) by licking themselves.
Jackrabbits use their huge ears in a similar way. A network of capillaries close to the surface fills with blood, which is cooled when the wind blows across the ears. This works, however, only when the air temperature is lower than the body temperature. Otherwise, they will gain heat!
In high heat, birds become less active and seek shade; some species bathe their feet and legs in water to cool the body. Vultures and cormorants spread their wings to cool off, while some large birds allow rising thermal air currents to carry them up to cooler altitudes.
Migration Patterns
Usually associated with the avoidance of winter, migration allows some animals to avoid summer heat as well. Chickadees, nuthatches, and juncos winter in plains areas and return to higher elevations in the spring to nest. Ruby-crowned kinglets migrate within Colorado from their wintering grounds in lowland riparian and piñon-juniper forests to spend the summer on the alpine tundra and in high-altitude coniferous forests.
Panting and Gular Fluttering
Panting is an important method of cooling for many animals, including birds. Air passes through the nose and mouth, and the resultant evaporation cools the tissues and blood. A robin can dissipate about one half of its metabolic heat on a hot day by panting. Numerous birds-pelicans, cormorants, pigeons, doves, owls, great blue herons, Gambel's quail, bobwhites-use a mechanism similar to panting called gular fluttering. This rapid movement of the throat skin aids panting and hastens evaporative cooling.
Body Size and Fur Insulation
For large animals, body size is itself a protection against heat. With a low surface-to-volume ratio, they take on less outside heat in proportion to their size. A very hot day that might quickly overheat a deer mouse might not elevate the temperature of a buffalo at all. It's like the difference in time it would take to boil a cup of water and a tub of water on the same temperature burner.
We usually think of fur as something to keep an animal warm and, therefore, to shed in summer. However, the qualities of fur make it an important insulator against heat when the outside air is hotter than the animal's body temperature. A protective fur coat also reduces water loss through the skin. Light coat color helps reflect, rather than absorb the sun's rays.
Next: Bats Need Your Help
(The information contained in these issues of Colorado's Wildlife Company was accurate at the time of original publication. Situations and circumstances described, staff positions, contact information, and dates of some events may have changed in the interim. Present knowledge and understanding of biological and behavioral facts and information may also be different, now, than presented here.)