Saturday, January 20, 2018
If asked to name the group of mammals to which biologists assign rabbits, many would answer “rodents.” But that would be incorrect. Rabbits, like the familiar cottontails we see in our backyards, and hares are lagomorphs, members of the mammalian order Lagomorpha (from the Greek, hare + form).
Any confusion between lagomorphs and rodents is understandable. Both groups are herbivores, and their skulls are superficially similar. They each have 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 peglike pair behind the much more conspicuous front pair. Rodents have a single pair of incisors. Second, the cheek bones of rabbits form a meshlike network of bone rather than a solid panel.
Rabbits and hares also have big feet and powerful hind legs that enable them to reach 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 teeth are spaced farther apart than the lower teeth. This requires lateral jaw action to chew food.
In North America, lagomorphs include 11 species of cottontails, eight species of jackrabbits and hares, and two species of unrabbitlike pikas that inhabit talus slopes in the high western mountains. The most widely distributed lagomorph is the eastern cottontail. The “bunnies” we see in our backyards are invariably eastern cottontails.
Cottontails begin mating in February, and 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 the nest after 14 days. Two weeks later the young are weaned and independent.
Meanwhile, mom has been busy. She mates shortly after giving birth, so she’s 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 one reason rabbits can withstand the heavy toll taken by predators and hunters.
Hares and jackrabbits have a longer gestation period, about 36 days, and the young are precocial at birth; that is, they’re fully furred and their eyes are open.
Cottontails spend most of the day resting in a “form” – a well-worn depression on the surface of the ground. It’s usually nestled in a clump of dense grass in a thicket or under a brush pile. Contrary to popular belief, cottontails do not dig burrows. They occasionally seek refuge in an abandoned groundhog den to escape predators or winter weather, but they spend most of their time above ground.
Jackrabbits inhabit western prairies, grasslands and deserts. Hares are adapted to colder parts of North America.
Snowshoe hares occur across the northern tier of states, including Michigan, New York and New England. They can also be found at higher elevations out west and along the spine of the Appalachians as far south as North Carolina. A fall molt turns their browner summer pelage to near snow white in winter, making them nearly invisible when snow covers the ground.
Perhaps the most fascinating aspect of lagomorph biology is diet. Though strict vegetarians, they also eat their own droppings. To increase digestive efficiency they recycle food that has already passed through their digestive system. This habit is called coprophagy.
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.
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.
Dr. Shalaway can be heard on Birds & Nature from 3 to 4 p.m. Sundays on 620 KHB Radio, Pittsburgh or live online anywhere at www.khbradio.com. Visit Scott’s website www.drshalaway.com or contact him directly at firstname.lastname@example.org or 2222 Fish Ridge Road, Cameron, WV 26033.