The phrase, "breeding like rabbits," refers to many types of overpopulation. How and when does a rabbit actually reproduce? They start early. The age of sexual maturity depends on size, with the average female, or doe, able to mate around 4 months of age. Giant breeds reach sexual maturity starting around the age of 6 months. A rabbit pregnancy lasts approximately one month.
In rabbits, sex triggers egg release, not hormonal cycles. This process, induced ovulation, also means that a rabbit can mate and become pregnant again soon after giving birth. Rabbits are mating receptive the majority of the time -- about 14 out of 16 days, according to the Merck Pet Health Manual. If the doe's vagina is moist and reddish, she's receptive. The days on which she is not receptive, her vagina lacks moisture and is a pink shade. Twelve days after mating, you can feel the bunny fetuses in the doe's abdomen.