You may have caught glimpses of this animal last night or early this morning.
Black-tailed Jackrabbits (Lepus californicus) are large hares. One of the main differences between hares and rabbits is that hares give birth to precocial young — the young (called leverets) are fully furred, their eyes are wide open, and they're ready to hop within a few hours of their birth. In contrast, newborn rabbits are naked, blind, and cannot leave the nest right away.
Jackrabbits have very large eyes, very long ears, and very long hind feet (see next two photos). They can run at speeds up to 35 mph and cover 2-3 meters with each bound.
The long ears (up to 8 inches) aid in hearing and in temperature regulation. Jackrabbits can increase blood flow to arteries in their ears to dissipate heat (via convection and radiation).
Researchers have used infrared images to document jackrabbit ear temperatures before and after exercise (see diagrams below). The first shows the ears at rest with temperatures less than 10°C. The second shows the change in ear temperature after exercise (such as a long night of delivering Easter eggs). Notice the much higher ear temperatures, up to about 35°C.
Figures adapted from Hill, R.W., D.P. Christian, and J.H. Veghte. 1980. Pinna temperature in exercising jackrabbits, Lepus californicus. Journal of Mammalogy 61: 30-38.
After being active through the night and early morning, Black-tailed Jackrabbits will rest in forms (shallow depression under shrubs) during the day. (Note the black dorsal stripe on the tail.)