"发情期的野兔" can be translated into English as "hares in heat" or "wild rabbits in estrus".
"Hares in heat" is a more colloquial and commonly used expression.
"Wild rabbits in estrus" is a more formal and scientific term, with "estrus" specifically referring to the period of sexual receptivity in female mammals.
Both expressions are accurate, and the choice between them may depend on the context and the desired level of formality.