All American Cottontail rabbits are species of Sylvilagus. There are thirteen slightly different kinds that live in the US and a few others that range all the way down through South America. Cottontail rabbits have also been introduced to France, Italy, Spain and Switzerland. They differ in the plants they have adapted to eat and in their size. Those that live in areas were food is less abundant tend to be a bit smaller. Mature female bunnies are 1-10% larger than the males. Cottontail rabbits mature very fast – some are ready to breed by the autumn of their first years while others do so the following spring.

At the first sign of spring, breeding season begins and doesn’t end until late summer. Cottontail mothers are pregnant for about 28-30 days. Neat the end of their pregnancy, females (does) will build a nest to give birth in. They prefer to build it in an open area where they cannot be approached unnoticed. In suburban setting, grassy fence borders, berry thickets, gardens and high grass lawns are often chosen. They are not shy about building very close to houses. There, she will dig a small oblong nest in soft ground about as big as the dimensions of her tummy. She lines the nest with grass and plant debris and lines that with her own fur, which she pulls from her stomach. About a week later, she gives birth to 2-7 babies in the nest that weigh about an ounce (28-38 gms) each depending on the number in the litter and the subspecies of cottontail. Average litter size is about four. Mother cottontails do not spend much time on their nest. During the day, when they are usually gone, they cover their nest with litter, returning only at night for short periods to feed the babies. They do this for the next 14-18 days until the babies are mature enough to leave the nest. The babies will stay hidden in the area of the nest for an additional week or two. This is the period when humans, dogs and cats find most of them.
The bunnies are fully weaned when they weigh 95-125 grams – depending on the subspecies and size of the litter. One in five or less will survive a full year.
Cottontails usually have several litters in a single season, building a new nest for each one.

On the Eastern Coast of the US, wild bunnies begin to breed about March, which is about the same time brush cottontail babies begin arriving in earnest in California.