Female animals regularly enter a phase where they are sexually active and receptive to males; this is known as the [[Female Reproductive Tract -Oestrous Cycle - Anatomy & Physiology|oestrous cycle]]. Some animals are able to reproduce all year round, but many have an anoestrus phase which requires a [[Female Reproductive Tract -Seasonality of Reproduction - Anatomy & Physiology|seasonal response]] for cycling to begin. In some species [[Reproductive Behaviour - Oestrus Behaviour - Anatomy & Physiology|detection of seasonal cycling]] can be crucial to productivity. | Female animals regularly enter a phase where they are sexually active and receptive to males; this is known as the [[Female Reproductive Tract -Oestrous Cycle - Anatomy & Physiology|oestrous cycle]]. Some animals are able to reproduce all year round, but many have an anoestrus phase which requires a [[Female Reproductive Tract -Seasonality of Reproduction - Anatomy & Physiology|seasonal response]] for cycling to begin. In some species [[Reproductive Behaviour - Oestrus Behaviour - Anatomy & Physiology|detection of seasonal cycling]] can be crucial to productivity. |