"发情期的野兔" can be translated into English as "a wild rabbit in heat" or "wild rabbits in the mating season" (depending on whether you're referring to a single rabbit or multiple rabbits).
"In heat" is a common expression used to describe animals that are in the reproductive or estrus stage.
"Mating season" is another way to refer to the period when animals are sexually active and ready to reproduce.
Choose the phrase that best fits the context of your sentence.