A female rabbit is considered to be in season if she accepts the advances of a male rabbit. If she declines, she is not in heat (estrus) and is considered to be in diestrus. Unlike most other mammals, female rabbits do not have a regular heat cycle; instead, they are almost permanently in heat, and they ovulate only after mating.
According to the Food and Agriculture Organization of the United Nations, a red vulva signifies 90 percent of the time that a female is in the mood to mate. However, the other 10 percent of the time, a female can have a red vulva without being in heat.
In contrast, if the rabbit's vulva is not red, she is only in the mood to receive service 10 percent of the time. Other signs indicating that she does not want to mate include backing into a corner or acting aggressively toward the male who is trying to mate with her.
If a female does not breed and ovulate, the follicles on her ovaries regress, and new follicles form. These follicles stay in a pre-ovulation state for a few days before regressing. Thanks to this cycle, the female rabbit is almost always ready to breed.