BACKYARD RABBITS
Easter Cottontail, Sylvilagus floridanus, picture by William R. James, courtesy of U.S. Fish and Wildlife ServiceIn most of the US -- everywhere except the western 1/3rd of the country and northern New England -- average backyards are occasionally visited by Eastern Cottontails, Sylvilagus floridanus. That's an Eastern Cottontail at the right. When most North Americans think "rabbit," this is the species we're visualizing.

However, Eastern Cottontails are by no means our only North American rabbits. According to the Peterson Field Guide A Field Guide to the Mammals : North America North of Mexico, here are the North American members of the Rabbit Family, the Leporidae:

  • Arctic Hare
  • Tundra Hare
  • Snowshoe Hare
  • European Hare
  • Whitetail Jackrabbit
  • Antelope Jackrabbit
  • Blacktail Jackrabbit
  • Eastern Cottontail
  • Mountain Cottontail
  • New England Cottontail
  • Desert Cottontail
  • Brush Rabbit
  • Marsh Rabbit
  • Swamp Rabbit
  • Pygmy Rabbit

Hares and jackrabbits are members of the genus Lepus, and generally have longer legs and ears than cottontails and rabbits. Cottontails and rabbits are members of the genus Sylvilagus. Hares are generally northern, cold-land species while jackrabbits typically live in arid desert conditions. The distinction between cottontails and rabbits is less clear.

RABBIT FOOD

Rabbits are nearly entirely vegetarian. In the summer, about 50% of the Eastern Cottontail's diet consists of grasses, including bluegrass and wild rye. They also like wild strawberry, clover and garden vegetables. In the winter, cottontails eat woody plant parts such as twigs, bark and buds of oak, dogwood, sumac, maple and birch. Feeding activity peaks 2-3 hours after dawn, and the hour after sunset.

THE RABBIT DIGESTIVE SYSTEM

A rabbit's digestive system is beautifully adapted for its vegetarian diet of rough, tough plant parts.When a rabbit eats, its food goes down the esophagus into the stomach. Not much happens in the stomach other than that the food is sterilized, and then it is moved into the small intestine. While in the small intestine up to 90% of the protein, starches and sugar are absorbed from the food.

After these nutrients are removed, the small intestine sorts what's left. Undigested fibrous material is passed into the colon, where it is formed into the hard, round pellets we often find in our gardens, for once the pellets are formed, they are defecated.

THE CAECOTROPH STORY

However, that's not the whole story, because when food is still in the small intestine, the unabsorbed, softer stuff (what isn't formed into hard, round pellets), instead of being forwarded into the colon, is shunted into a special pouch known as the caecum (SEE-kum). In the caecum, anaerobic bacteria (bacteria not needing oxygen) ferment the material, breaking it down better and forming vitamins and proteins. Part of this is absorbed into the rabbit's body, but some is left, and this is then formed into a second kind of pellet. These pellets are soft and moist instead of hard and dry like the other pellets, and are known as caecotrophs. Once the caecotrophs are formed they are emptied from the caecum into the colon, and then excreted.

Therefore, rabbits excrete two kinds of pellets, one being hard, dry and spherical (the ones we find in our gardens), and the others, the caecotrophs, being soft, moist and clustered together like grapes.

We seldom see caecotrophs, however, because they are typically expelled at night and, more importantly, the rabbit quickly eats them, typically taking them directly from its own anuses. Of course this is done to recycle the material, to assure that nothing is wasted.

You might want to remember this the next time you have the urge to kiss a cuddly-looking cottontail on the snout...

COTTONTAIL FAMILIES

Female Eastern Cottontails, called does (rhyming with rows), produce from 3-4 litters per year. Litter size varies from 2 to 8, with an average of 5.6 baby rabbits per nest. Therefore, if a female cottontail produces 3.5 litters of 5.6 young each year, that's 19.6 rabbits a year, and a cottontail may live for three years or more! Obviously, a lot of rabbits never reach their third year, else the world would be overrun with them. Predators who keep their numbers under control include hawks, owls, foxes, coyotes, and domestic dogs and cats.

RABBIT SKULLS

The other day I found a skull I wanted to identify. On the Internet I found an address where they invited people to send skull pictures for free identification. Apparently thet organization is associated with the Museum of Osteology in Oklahoma City. (http://www.museumofosteology.org)

The next day, the Director of Education there, wrote back saying that the skull belonged to a rabbit. He even returned my own picture highlighted and labeled to show what made the rabbit skull a rabbit skul. That's it below:

rabbit skull showing rostral fenesration and two sets of incisors

He wrote:

Rabbit and hare skulls (Lagomorphs) are easily distinguished by two skull characteristics:

  1. Rostral fenestration... which is all the holes in the side of the animal's "snout" or rostrum, and
  2. A double set of upper incisor teeth.

That Museum of Osteology web address is worth holding on to.