This is called a 'warren'. Cottontails do not live in warrens. Each rabbit digs out a depression or hole in the ground big enough to hide itself well. This simple nest is called a 'form'. They dig the form to hide and shelter themselves and their young bunnies.
Cottontails eat mostly green plants of all kinds, including poison ivy.
During the winter, if food is very short, they will gnaw the twigs and bark of trees and shrubs. Cottontails mate as early as mid-February. In the northern limits of their range, they begin mating in March. The first litter of four to seven bunnies is born 26 to 28 days later. The mother lines the 'form' with dried, soft plants.