Nature Column: Learning About Rabbits
Thanks to cartoon characters such as Bugs Bunny, the rabbits we see in our backyards, eastern cottontails are familiar to almost everyone. And yet I suspect that most people think they are rodents. They are not. Rabbits and hares are lagomorphs, members of the mammalian order Lagomorpha.
The confusion is understandable. Both groups are herbivores, and their skulls are superficially similar. Each has a large gap between the incisors and molars, but a closer look at a lagomorph skull reveals two key differences.
First, lagomorphs have two pairs of upper incisors. A small peg-like pair sits behind the much more conspicuous front pair. Rodents have a single pair of incisors. Second, the check bones of rabbits form a mesh-like network of bone rather than a sold panel.
Rabbits and hares also have big feet and powerful hind legs that enable them to leap to top speeds almost instantly even from a resting position.
And if you’ve ever watched a rabbit eat, you may have noticed that its jaws move side to side. That’s because their upper rows of teeth are spaced farther apart than the lower rows. This requires lateral jaw action to chew food.
In North America, lagomorphs include two species of unrabbit-like pikas that inhabit talus slopes in the high western mountains, 11 species of cottontails, and eight species of jackrabbits and hares. The most widely distributed species is the eastern cottontails. The “bunnies” we see in our backyards are invariably eastern cottontails.
Cottontails spend most of the day resting in a “form” – a well-worn depression on the ground. It’s usually nestled in a clump of dense grass in a thicket or under a brush pile. Contrary to popular belief, rabbits do not dig burrows. They occasionally seek refuge in an abandoned groundhog burrow to escape predators or harsh weather, but they spend most of their time above ground.
Cottontails began mating in February. Females give birth to their first litter after a pregnancy of 28 to 30 days. Prior to birthing, the female digs a shallow hole about the size of a clenched fist. She lines the nest with fur plucked from her belly and covers the hole with grass to camouflage it from above.
Four or five blind, naked young grow rapidly and leave after 14 days. By the age of one month the young are weaned and independent.
Hares and jackrabbits adopt a different strategy. After a 36-day gestation period, the young are precocial at birth. They are born fully furred with eyes open and leave the nest within hours of birth.
Meanwhile, mother cottontails keep busy. They mate shortly after giving birth, so they are pregnant with a second brood while nursing the first. A single female can breed five or six times in a year and produce up to 35 babies. This is a major reason rabbits can withstand the annual toll taken by predators and hunters.
Perhaps the most fascinating aspect of rabbit biology is their diet. Strict vegetarians, cottontails enjoy succulent greens such as dandelion leaves, clover, and grasses as well as the bark of woody species such as raspberry, apple, black cherry and sumac. They can consume up to 40 percent of their body weight every day. Evidence of rabbit browsing is easy to recognize. Their sharp incisors clip woody twigs cleanly and leave behind a distinct diagonal cut; deer break twigs off and leave behind ragged edges.
A vegetarian diet, however, is hardly unique. What makes rabbits different is they are also coprophagous – they eat their own droppings. Cottontails increase digestive efficiency by recycling food that passes through their system.
Rabbits excrete two types of droppings. After a meal first passes through the digestive system, rabbits pass soft, green “food” pellets, which they reingest as soon as they are dropped. This also minimizes their exposure to predators because they can leisurely consume droppings from the safety of dense cover.
During the second trip through the digestive system, vitamins and other nutrients that were not absorbed the first time are assimilated. The familiar piles of dark, round pellets you find in the backyard are the true end products of rabbit digestion.
Send questions and comments to Dr. Scott Shalaway, 2222 Fish Ridge Road, Cameron, West Virginia 26033 or by email at firstname.lastname@example.org