Despite their name, jack rabbits aren't true rabbits. They are hares, distinguished by long, arched backs and extra-large hind feet. The long ears from which they got their name after being likened to jack donkeys are essential for survival, both for cooling and for hearing predators approach. Compared with humans, they have relatively short lives, but they make up for it by reproducing rapidly.
As solitary animals, jack rabbits don't spend time together before or after mating. During mating periods, however, the males and females chase each other in a playful manner before actually mating. Females usually mate multiple times per year, having between four and six litters every year, depending on climate conditions. In temperate climates, jack rabbits breed year-round, but in colder areas breeding takes place between December and September.
The gestation period varies slightly between species but is typically around 40 days. The white-tailed jack rabbit (Lepus townsendii), which is the most common, has a gestation period of 36 to 43 days, with the average being 42 days. The black-tailed jack rabbit (Lepus californicus) has a slightly longer gestation period, lasting 41 to 47 days with an average of 43 days. Litter sizes vary greatly depending on the individual rabbit; litter size for a white-tail jack rabbit ranges from one to 11 and averages five; the black-tail jack rabbit normally has one to eight young per litter, averaging two or three.
Unlike true rabbits, who are born bald and helpless, a jack rabbit gives birth to young who are already well-furred and open-eyed. The mother does not build a regular nest but places each baby in a separate hiding place. This way, if a predator finds one of the young, the others are not at risk. She nurses the babies a few times each day for only the first two to three days and does not typically provide any care after that time.
Young jack rabbits, called leverets, remain in their hiding places, eating nearby vegetation, for the first two to three weeks of their life. Around 21 days old, depending on species, they begin to venture out into the world and behave much as adults, foraging for food in the evenings and hiding in small bushes or clumps of grass during the day. Juvenile jack rabbits grow rapidly during this time.
Depending on the species and sex, jack rabbits reach full adult size between about 8 and 12 months. They become sexually mature and capable of breeding about this time. Females will often instinctively wait until the following breeding season to begin mating. Thanks to this instinct, they are normally at least 1 year old before they have their first litter. A jack rabbit can live up to 8 years, but the normal life span in the wild is 5 or 6 years.