Reproductive behavior is an obligatory component of the reproductive process.  It consists of precopulatory, copulatory and postcopulatory stages.  In the female sexual receptivity occurs only during estrus and is characterized by distinct behavior and mating posture (lordosis).  In the male, reproductive behavior can occur potentially any time.  Sexual arousal in the male involves a cascade of endocrine and neural events that result in erection of the penis, mounting of the sexually receptive female, intromission and ejaculation.  Erection of the penis involves specific neural and biochemical events that culminate in penile vasodilation.  Ejaculation is a reflex that is initiated by stimulation of  the glans penis and concludes with expulsion of semen.