The rock squirrel (Spermophilus variegatus) is the largest of the three, up to 1.5 pounds. It resembles eastern tree squirrels. This squirrel is grey with reddish to brownish tinge, usually on its back. It has a large bushy tail. Rock squirrels are found in many habitats, except for the driest part of the desert. They are true omnivores, feeding on seeds, mesquite beans, insects, eggs, birds, carrion, as well as cactus fruit.

I have seen them kill and eat snakes. Upon encountering a snake, a rock squirrel will stamp its feet and wave its tail from side to side while facing the snake. It also tries to flick sand or dirt in the snake’s face with its front paws. This behavior is called mobbing. Researchers in California note that rock squirrels can distinguish between venomous and non-venomous snakes, and change their mobbing behavior accordingly. Yes, they will attack rattlesnakes. Apparently, adult rock squirrels can at least partially neutralize rattlesnake venom. Rattlesnakes have heat-sensing organs which can detect a difference in temperature as little as 0.01 F at one foot. There is some research that suggests that rock squirrels take advantage of this. The squirrel can pump extra blood into its tail to make the tail warmer than its body, thereby fooling the snake into striking at the tail rather than the body.

Rock squirrels dig burrows and may be colonial or solitary. They can be very territorial. They mate in early spring and produce a liter in March. Sometimes a second litter appears in August or September. The rock squirrel may become dormant, holed up in its burrow during cold times, but it is not known to hibernate.

The round-tailed ground squirrel (Spermophilus tereticaudus) resembles a miniature prairie dog, and like them, is a very social animal that lives in small colonies. It is usually grey to beige with a long, black-tipped tail. Adults weigh 6- to 7 ounces. They inhabit valleys and alluvial fans. The round-tails are primarily herbivores, feeding on grass seed, cactus, and other nearby vegetation such as spring flowers, but they will eat carrion. They may sleep for a few weeks in summer until the monsoon arrives. The round-tailed ground squirrel hibernates in the winter. The round-tails are champion small miners. They may have an extensive tunnel network with multiple entrances. They too breed in early spring with pups born in March or April. The pups usually emerge with their mother by May.

The Harris’ antelope ground squirrel (Ammospermophilus harrisii) resembles a chipmunk, but it has a white stripe on its side that chipmunks lack (but chipmunks have white stripes on their faces). Also, chipmunks live at higher elevation, not on the desert floor. This squirrel seems to prefer rocky areas. The Harris’ antelope squirrel usually feeds on cactus fruit, seeds, and mesquite beans, but it will take insects and mice. They will climb a barrel cactus to get the fruit in spite of the spines. The Harris’ antelope squirrel is active all year. During hot days, it uses its busy tail to provide some shade. They did burrows about three feet deep where conditions allow.

All three squirrels have sharp, strong claws used for digging. All three are diurnal, that is, they are most active during the daytime. They all have cheek pouches to store food as they gather it. These squirrels have a variety of vocalizations, some quite loud. You might mistake the sound for a bird call.

The barn owl is a very adaptable bird of prey that is found in specific habitats on all continents except Antarctica. It is the most widely distributed land bird. Barn owls eat rodents, and perhaps because we humans attract such beasties, barn owls favor nesting near human habitation in barns, under bridges, in mine shafts, and in palm trees. In the southwest, barn owls also nest in undercuts in arroyos, and may be found in desert grasslands, and in trees around agricultural fields.

Barn owls often swallow their prey whole, but they can’t digest fur and bone, so they regurgitate pellets. (Dissection of pellets allows researchers to study what the owls eat.)

Barn owls are sexually dimorphic, that is, the males and females have differing plumage as you can see in the photos. The females tend to be bigger, darker, and more speckled than the males. The birds average about 12 inches in body length and have wingspans of about 33 inches. Weights in adults vary from 10 to 20 ounces.

The feathers form a facial disk designed to focus sound to the owl’s ears. The ears themselves are not symmetrical on the skull as in other animals. Rather the left ear points downward, and the right ear points upward. Therefore, sound reaches each ear at slightly different times and allows the owl to exactly pinpoint the source. Some researchers claim that each ear hears with slightly different frequency sensitivity. That also aides in sound location. Barn owls are smart and learn all the squeaks and twitters of their prey so that they can identify not only where it is, but also what it is. Perhaps the only rodent with equally good hearing is the Kangaroo Rat.

Birds have four toes or talons. They are configured either three in front – one in back, or two and two. The barn owl can move its outer toes to form both configurations. That enables the owl to form a good web-like trap when snatching prey. The barn owl has serrations on the claw of the middle toe to aid grooming.

Barn owls have many vocalizations, some researchers count as many as 15 distinct calls as well as tongue clicking and wing clapping. Some of the sounds are for proclamation of territory, others are for alarm, and some are for courtship and mating rituals. Many of the sounds are screaming or screeching; others include hissing or wheezing, and whistling. None of the sounds are what we would call an owl hoot.

Nesting occurs in the spring in most areas, but can occur any time of year if there is abundant prey available. The female may lay up to six eggs each one to two days apart. Incubation takes 33 days and the young hatch one to two days apart. If the parents don’t provide enough food, the older chicks starve out and may even consume the younger chicks. The chicks will fledge seven to eight weeks after hatching. Barn owls typically breed at an age of one year, and there is a high mortality rate in the wild. Typical wild life expectancy is 2 years, but captive birds have lived into their high teens.

Barn owls are difficult to observe in the wild because of their nocturnal habits. I have seen them sleeping in mine shafts. If you want to seem them close up, go out to the Arizona-Sonora Desert Museum where Docents frequently have them on display.

The diet is almost exclusively seeds, and it prefers seeds high in carbohydrates rather than seeds high in fat or protein. That’s because metabolizing fatty seeds produces heat, and metabolizing protein-rich seeds requires more water to get rid of nitrogen-rich waste products.

The K-rat stores seeds in its burrow where they absorb any humidity, thereby giving the rat some extra moisture. The K-rat has no sweat glands through which to lose water.

The kangaroo rat minimizes moisture loss during respiration with its specialized nasal passages which function as counter-flow heat exchangers. These passages warm the air during inhalation, then cool the air and extract moisture during exhalation.

The kangaroo rat can conserve water by producing urine about 5 times more concentrated than human urine. The rat also produces very dry feces pellets with about one-fifth the water content of a white lab-rat’s pellets.

The kangaroo rat is 4- to 5 inches long with a tail up to 10 inches long. It prefers to hop on its hind legs. It can jump 10 feet and change direction immediately upon landing, something that helps it avoid nocturnal predators.

Although the rat has tiny external ears, the middle ear chamber is highly developed and may be bigger than the braincase itself. This allows the rat to hear low intensity and low frequency sounds such as an owl flying or a rattlesnake ready to strike. This, together with its ability to jump 10 feet, helps it avoid predators.

There are several species and most inhabit the grasslands of the great plains, but at least one species is a desert dweller. The Northern Grasshopper mouse has a range from Canada to Mexico, and California to Minnesota; the Southern Grasshopper mouse has a range that includes parts of Nevada, Arizona, New Mexico, and Texas. The southern species is gray-brown- to cinnamon colored with a short white-stripped tail. Most grasshopper mice are relatively stout compared to other mice. The head and body is 3.5″- to 5″ and the tail is 1″ to 2.5″ long.

Usually a male-female pair live together and defend a territory. It marks the territory with musk.

Grasshopper mice have very strong jaw musculature required for killing prey. And they learn quickly how to deal with various prey. One observer describes how the mouse dealt with a 3-inch scorpion in Arizona: ” The mouse would first nip the tail so that the stinger was ineffective. It would then stand the scorpion on end, holding it with its front paws, and methodically eat the writhing creature head first.”

The grasshopper mouse is a nocturnal hunter, a good climber, and active year round. In some areas, scorpions account for almost their entire diet, which might be surprising because the mice are not known to have any immunity to scorpion venom.

These mice will eat seeds, grasses, and grains, and cache them, like other mice, but about 90% of their diet is animal matter. The strangest part of their diet is sand. Biologists think the mice eat sand to aid in digestion, just like some birds ingest gravel. And that’s not all that is strange about their digestive system. As described in an article by Mary Ingle: “A pouch attached to the underside of the stomach opens into it via an aperture too small for large food particles to pass through. The pouch contains all of the gastric glands that contribute to the breakdown of food and are normally found in the stomach of other mammals.” Ingle speculates that the pouch exists because the insect diet would be too rough and damaging for delicate gastric glands to function normally.

The grasshopper mouse digs four kinds of burrows: nesting, retreat/sleeping, caching, and the bathroom.

The mice have several vocalizations. You may have heard their territorial proclamation and mistaken the high-frequency sound for that of an insect. So now, when you are out at night, listen for the mouse that roars.

For a video of a battle between a grasshopper mouse and a very large centipede check here: http://tinyurl.com/ylyme9w Note that centipedes are venomous.

Tarantulas are primitive spiders that evolved almost 350 million years ago and have changed little since. The female Desert Tarantula is usually tan or brownish, while the male is darker, usually with black or dark legs and a reddish abdomen. Females have a large abdomen, bigger than the cephalothorax(upper body), while the males have a small abdomen.

Tarantulas dig burrows about 6 inches deep and up to 8 inches laterally, enlarging them as the spider grows. The spiders molt 3- to 6 times a year as they grow, and they can regenerate lost legs upon molting.

Tarantulas are venomous like all spiders, but they are very docile and bite only under extreme provocation. I have picked up many tarantulas and never have been bitten. The venom is usually not harmful to humans. But tarantulas have another defense. Some of the hairs on their abdomen are barbed (urticating hairs) and are very irritating. The tarantula uses its hind legs to flick these hairs at an attacker.

 Tarantulas are long lived spiders. They reach sexual maturity at 8- to 12-years old. Females can live up to 25 years, but the males live only one season beyond sexual maturity. Mating takes place in the summer and fall, and the female stores the sperm until the next spring. The female spins a thick layer of silk in her burrow and in concealed places near the burrow to hold up to 300 eggs. Ants are the main predators of the eggs. The spiderlings hatch in about three weeks and stay in the silk cocoon for another 7 weeks while they grow. The survivors disperse and make their own burrows.

When active, tarantulas may set out strands of silk, “trip wires” around their burrow as a signal that a meal is passing by. They don’t like water, and flee if the burrow gets wet. Sometimes a silk cap on the burrow helps keep water out. Tarantulas do need to drink, but can go up to 90 days without water. During the winter, tarantulas become dormant. They plug their holes with silk and soil, and wait for summer.

And now for a gruesome tale. The Pepsis wasp, Pepsis formosa, is a large (up to 2 inches), bluish-black wasp with orange wings. It is also know as the tarantula hawk. It is a parasite on tarantulas and uses the spiders in its reproductive cycle.

The Pepsis wasp will approach a tarantula and cause the spider to rear its legs, thus exposing its abdomen. The wasp will sting the spider to paralyze it. The wasp will lay an egg on the paralyzed spider and drag it to a hole, bury it, and cover up the hole. When the wasp egg hatches, the larvae eats the flesh of the living tarantula for about 35 days, then spins a cocoon and pupates over the winter. If the wasp egg fails to hatch, the spider can recover. These large wasps generally don’t bother humans.

Tarantulas may look scary, but they are very gentle creatures. You need not be aftraid.