Genus Ammospermophilus, Antelope Squirrels
Antelope squirrels or antelope ground squirrels of the genus Ammospermophilus are sciurids found in the desert and dry scrub areas of south-western United States and northern Mexico. They are a type of ground squirrel and are able to resist hyperthermia and can survive body temperatures over 40 °C (104 °F).
There are currently five recognized species (see galleries below for all species except Espiritu Santo Antelope Squirrel):
Espíritu Santo antelope squirrel (A. insularis) found on Isla Espíritu Santo, Mexico. Some authorities treat it as a subspecies of A. leucurus. (Not pictured below)
Harris's antelope squirrel (A. harrisii) found in Arizona and New Mexico in the US, and Sonora in Mexico.
San Joaquin antelope squirrel or Nelson's antelope squirrel (A. nelsoni) found in the San Joaquin Valley, California.
Texas antelope squirrel (A. interpres) found in Texas and New Mexico in the US, and in Mexico.
White-tailed antelope squirrel (A. leucurus) found in the southwestern United States and Mexico's Baja California Peninsula.
The below galleries are of the four extant species of Ammospermophilus found in the USA:
Harris's antelope squirrel (Ammospermophilus harrisii) is a species of rodent in the family Sciuridae. It is found in Arizona and New Mexico in the United States, and in Sonora in Mexico. They are adapted to hot weather conditions including a technique called "heat dumping". They have a wide-ranging diet, including both vegetation, insects, small rodents and carrion.
The species is named after Edward Harris. Examples of A. harrisii have distinctive markings on their grey fur, with brown highlights on the sides and legs and a white strip down the side of the torso and encircling their eyes. Their fur grows longer in the winter than it does in the summer. Adults weigh around 4–5 ounces (110–140 g), and measure 8.5–10 inches (22–25 cm) minus their tail, which measures 3–4 inches (7.6–10.2 cm). They can be mistaken for chipmunks.
A. harrisii has a high body temperature of 97-107 degrees Fahrenheit (36.7 - 41.6 °C) In order to protect itself from the heat of the Sonoran Desert, A. harrisii carries their tails over their bodies in order to provide shade. A. harrisii also participates in a heat reduction method where individuals move into shaded positions and lie spread eagled against the ground. This is referred to as "heat dumping". They are active during the day, and do not sweat but otherwise reduce temperature by salivating.
The optimum reproductive period for A. harrisii is between February and March although mating can take place between December and June. Gestation lasts thirty days, and females usually have one litter per year with an average of 6.5 pups. Newborns grow to adult size at around 217 days after birth. Both males and females reach sexual maturity during the first year.
The habitat of A. harrisii ranges across the Southwestern United States, specifically in Arizona and the southwest of New Mexico. The range extends outside the US into Mexico into the northwest of the state of Sonora. They are designated as a non-game animal by the Arizona Game and Fish Department. While the species is not endangered, the range of its habitats is being reduced by human developments.
Their diet includes the fruit and seeds of local cactus plants, as well as beans of the mesquite plant. They do not only eat vegetation, and also consume insects, small rodents and carrion.
Harris’s Antelope Squirrel (Ammospermophilus harrisii) - Photographed in the Sonoran Desert Museum Grounds, Tucson but seen in many locations in Arizona.
The White-tailed antelope squirrel (Ammospermophilus leucurus) is a diurnal species of ground squirrel, scientifically classified in the order Rodentia and family Sciuridae, found in arid regions of the southwestern United States and the Baja California Peninsula of northwestern Mexico.
The white-tailed antelope squirrel's geographical range extends north to south from southwestern Oregon to New Mexico, and east to west from western Colorado to Baja California, Mexico.
This species of squirrel has an average home range of 14.9 acres (60,000 m2), and utilizes approximately 4 acres (16,000 m2) in its daily activities. Throughout much of the squirrel's range, especially in Utah, the population density fluctuates greatly, with periods of high density followed by periods of low density. Average population density also varies by season, with higher density in autumn relative to late spring.
The white-tailed antelope squirrel is commonly spotted in arid habitats throughout the southwestern United States. Throughout this range, Ammospermophilus leucurus is omnivorous, feeding primarily on foliage (10%-60% of its diet), seeds (20%-50%), arthropods, and to a lesser extent, vertebrates (mainly lizards and rodents; predatory behavior by ground squirrels has been noted). In conjunction with being a predator, the white-tailed antelope squirrel is also prey to many larger animals, including raptors, various canids, and snakes. These squirrels are not only preyed upon by large predators, but they also fall victim to many diverse ectoparasites. These include various ticks, fleas, mites, lice, and a couple species of parasitic larvae.
Antelope squirrels are active most during the cooler parts of the daylight hours, avoiding midday as much as possible. Although these animals live in hot and arid climates, the white-tailed antelope squirrel is diurnal, meaning heat gain from metabolic activity could be a problem. However, compared to direct exposure of heat from the sun, metabolic heat gain contributes little to the overheating of this species. This diurnal activity pattern may be contributed to predation patterns. Selective pressures may have led to this species avoiding nighttime activity due to increased predation by nighttime predators. This behavior is controlled by the squirrels' natural circadian rhythms, and research has shown these rhythms to be highly important in keeping these diurnal activity patterns intact.