The Peninsular desert bighorn is truly a remarkable animal. From the massive curl of a ram’s horns to their agility in steep rocky terrain, they create a sense of awe. But of all their unique characteristics, the ability to survive in the desert’s harsh environment may be the most fascinating.
Over the centuries, bighorn sheep have evolved special adaptations in order to endure
the demanding conditions of the desert. Both physical and physiological (organs, tissue, etc.) specializations are necessary to withstand the searing heat of summer
and limited supplies of drinking water.
One physical characteristic which aids the bighorn to endure the desert’s blistering heat, is their tan colored pelage (hair coat). This light coloring enables the sheep to reflect approximately 40% of the sun’s rays, thus reducing their surface heat intake.
Desert bighorn are able to dissipate heat primarily through their respiratory tract by panting. Although bighorn do have functional sweat glands, it is thought that only a small fraction of the heat dissipated is actually derived from sweating.
One obvious way they help reduce the heat load is to avoid direct sunlight. To do this, bighorn will often bed down in shaded areas when available and remain relatively inactive during the hottest portion of the day and seek out shade where possible.
One of the most crucial factors for the desert bighorn, as with other desert species, is the availability of water. Despite the unique adaptations described previously, an adequate water balance must be maintained within the body to avoid dehydration. Most animals are unable to tolerate losing more than 10% of their body weight in fluid before dehydration results. However, it is felt that desert bighorn can lose up to 30% fluid weight and still function. One of the physiological means to aid in conserving water, are their highly efficient kidneys. Their kidneys regulate internal water so that only a relatively small amount of fluid is lost from the body (usually in the form of urine).
Another unique physiological adaptation is the ability to utilize water contained within their food, such as barrel cactus. In cooler seasons, bighorn can go without drinking water for months at a time as they get their necessary electrolytes from their diet. However, during summer, bighorn will often choose to drink daily when possible, although they can go without drinking water for 3 days in 100 degree temperatures. When water is available, they may consume nearly 20% of their body weight in a comparatively short period of time.
These are only a few of the extraordinary adaptations that bighorn have acquired for desert survival. In order to ensure the continued existence of the Peninsular desert bighorn, it is critical that we protect the habitat in which they live.