Naturalist View June 2010

Adapting to the Heat

One warm afternoon last summer, I was trying to get a picture of a SGB (Small Gray Bird) with my telephoto lens. This bird was busy hunting for food, and like most SGB’s, would not pose for any length of time for a photo. I am a reasonably patient man (ha!), but this bird kept in the shade. I thought that it would soon land in a sunny spot so that I could get the shot I needed for identification. It became evident that this was not happening. Eventually it dawned on me that what I was observing was an adaption that this bird had made to the summer heat. By staying in the shade, it could keep from overheating as it was gathering food. I observed this bird over the next few days and found that this behavior was consistent; it never did give me an opportunity to take the picture I wanted.Nature always has found ways to adapt to environment. The big challenges for adapting to the Sonoran Desert are the heat and water. Let’s take a look at how some local animal species adapt to our area.

A nocturnal lifestyle, which keeps them out of the heat of day (and out of human sight as well). The mountain lion is a good example. The wide variety of prey the cougar hunts ranges from rodents and rabbits to cattle and deer. This solitary animal can travel miles in search of food. The mountain lion has adapted itself well to the environment of the Sonoran Desert. It only hunts during the night, while during the heat of the day it takes shelter in caves and crevices in the mountains. You may be more familiar with the nocturnal roaming of the Javalina, the ringtail cat or the desert toads. Even the small rodents such as the white-throated wood rat (pack rat) are essentially nocturnal.

Living in burrows, which are cooler and more humid.This often goes along with the nocturnal lifestyle, and the burrow becomes a place to sleep during the hot day. Burrow diggers are called fossorial. One of my favorite fossorial residents is the round-tail ground squirrel. Round-tailed ground squirrels are social, living in small colonies. They hibernate through the winter months, emerging in early February to take advantage of the new spring growth. They breed shortly after coming out of hibernation; 6 to 7 young are born in March or April. By May, the youngsters accompany the mother to the surface. The young come out for several hours of playing and feeding until the temperatures rise; then they return to their burrows until late in the afternoon when temperatures start to cool. They stand on their hind legs trying to get a better view as they watch for their many predators. Because they depend on vegetation for moisture, these squirrels estivate (Estivation is another form of dormancy, or "sleep") for a few weeks during the summer drought, until the summer rainy season again brings new growth and food.

Slender bodies with long limbs - are better for shedding heat. Snakes and lizards are good examples. They can move from one shady spot to another without absorbing as much heat. Lizards run by lifting their bodies and running on their tip-toes to keep their body from coming in contact with the hot ground. You may have noticed lizards doing push-ups. These are complex forms of lizard communication which can mean such things as “Hello, Gorgeous” or “Get your skinny rump off my rock.”

Adaptations for reducing water loss - specialized snouts and efficient kidneys are all part of this strategy. Some animals - i.e. the kangaroo rat - are so efficient that they never need to drink liquid water; they get all their water from the food they eat (including the water released when sugars are respired to form CO2 and water). Kangaroo rats have large cheek pouches that open on either side of the mouth and extend back to the shoulders. They fill the pouches with food, such as dry seeds, and then empty them by turning them inside out, like pockets. The overall color of the kangaroo rats can be anywhere between pale, sandy yellow, to dark brown, with a white underside. Tails tend to be dark with white sides and a tuft of longer hairs. A feature of the kangaroo rat is the animal's efficient kidneys. The kidneys recycle almost all of the water which is retained by the body. Even the nasal passage of the Kangaroo rat is large flat and convoluted so that H2O exhaled in the breath is condensed and reabsorbed. They also do not urinate and as a result do not have the strong odor of other rodents. Kangaroo rats lose water mainly by evaporation during gas exchange, and so have developed a behavioral adaptation to prevent this loss. As they spend a lot of time within their burrows to escape the heat of the day, the burrows become much more humid than the air outside (due to evaporative loss). When collecting seeds, they store them in the burrows rather than eating them right away. This causes the moisture in the air to be absorbed by the seeds, and the kangaroo rat regains the water it has previously lost when it then consumes them.

Because of this tremendous concentration ability, kangaroo rats never have to drink; the H2O produced metabolically within their cells during oxidation of foodstuff (food plus O2 yields CO2 + H2O + energy) is sufficient for their body. Also, kangaroo rats cannot lose water by perspiring, because they have no sweat glands. Kangaroo rats lose water mainly by evaporation during gas exchange, so have developed a behavioral adaptation to prevent this loss. As they spend a lot of time within their burrows to escape the heat of the day, the burrows become much more humid than the air outside (due to evaporative loss).

These are just a few examples of animal adaption. Keep in mind that any plant or animal that is native to the area has made the adaptations necessary to survive here. Learning about these adaptations is a lifelong fascinating mystery.

Wrestling Rattlers

Several people sent me these pictures taken by Saddlebrooke resident Linda Andrews. This was not a mating dance but was a “Combat Dance”. In the spring snakes are looking for a mate. In the snake world this accomplished with a sense of smell. A male will come across the “perfume” of a mature female and follow the scent to locate her. Since several males may be “on the trail” they often come across each other. In the case of rattlesnakes this may result in a dominance display or serpentine wrestling contest, rearing and falling and body slamming until one or the other concedes defeat and leaves the area. Once inseminated the female, after a gestation of 167 days will bear her brood live, in late summer. The young are born complete with fangs and venom, armed and dangerous at birth.

The Western Diamondback Rattlesnake, Crotalus atrox, Crotalus comes from the Greek word crotalon meaning a rattle or a little bell; atrox comes from the Latin word atroc which means hideous or savage. Actually I find Rattlesnakes to be rather beautiful and certainly not savage. They have no desire to be near you or to waste their precious venom on something far to big to swallow.