The enormous ears of black-tailed jackrabbits gather the faint sounds of stealthy predators and radiate heat in summer, but they also provide a safe haven for ticks. Photo by Jeff Mitton
By Jeff Mitton
A black-tailed jackrabbit crouched in the sand, eating juniper berries that had dropped from the tree above. This jackrabbit lived in the Paria Canyon of southern Utah, but the species is abundant in the Great Basin, Colorado Plateau and Great Plains from shrub-grasslands up into pinon-juniper woodlands, though rarely into conifer forests with closed canopies.
Black-tailed jackrabbits, Lepus californicus, are hares, not rabbits.
One of the salient distinctions between hares and rabbits is that hares are precocial, born covered with fur and with their eyes open. They are born in a shallow depression in the shade of a shrub and are up and about within a day.
In contrast, the altricial offspring of rabbits are born in an underground burrow, naked, blind and unable to walk. Adult jackrabbits are called bucks and does, and their offspring are called leverets. The name jackrabbit was derived from the initial appellation "jackass rabbits," referring to their enormous ears.
Jackrabbits have a set of adaptations that suit them to arid and semiarid environments: a spartan diet with little water, camouflage, eyes on the sides of their heads, furry feet, agile flight and enormous ears.
Jackrabbits are herbivores able to thrive on some of the most defended and unappealing plants around them. They consume big sagebrush, rabbitbrush, black greasewood, mesquite, opuntia, saguaro, yucca, four-wing saltbush, creosotebush and many of the tougher grasses. They nibble coarse leaves and twigs with two pairs of upper incisors, one set directly behind the other, that grow continuously. Fifteen jackrabbits eat as much food each day as a large cow.
Jackrabbits, like rabbits and pika, are coprophagous, meaning that they eat feces, but not all forms of feces. Jackrabbits excrete two forms of pellets. When food passes through the first time, the droppings are green, soft and moist. These are immediately eaten to capture the moisture and some vitamins produced by intestinal bacteria. The second time around the droppings are brown, dry and devoid of nutritional value.
A long list of predators have jackrabbits high on their shopping lists: coyotes, red and grey foxes, mountain lions, bobcats, eagles, hawks and owls. Like many herbivores, jackrabbits are constantly wary and have their eyes on the sides of their heads, allowing them to look back, to the side and forward without moving. Their fur, colored dark buff with subtle black markings, provides excellent camouflage against many soils.
When camouflage fails, they flee. A slender body, long limbs and enormous feet suggest high speed and agility, but nevertheless, a jackrabbit's escape is a marvel to behold. They can attain 40 mph while jitterbugging around shrubs and cacti. Their speed is amazing but their endurance is not great, so crafty and persistent coyotes frequently bring them down.
Furry feet provide insulation against the sand and gravel heated by the blazing sun.
Their ears are enormous. They certainly hear well, but a jackrabbit's ears also function as radiators. After a sprint and on hot days, they increase the blood flow through the ears to dump heat. On cold nights, they reduce blood flow through the ears, preserving heat.
Ticks love their ears. If a tick attaches to a shoulder or the side of the neck, they can be scraped off with the nails on the hind feet. But ticks on the ears are safe, for the ears are so soft and malleable that they cannot be scratched hard. The jackrabbit that inspired this column had six ticks on its ears.
Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.
March 18, 2011