seasonal breeders are those who mate(a sexual partner of bird) only during certain time of year. eg:- sheep
As the day length decreases going from summer into winter, the increase in melatonin production cues the development of reproductive function in both the ovaries of hinds and the testes of stags, leading to the mating season (rut) in autumn. This is why red deer and wapiti are often referred to as ‘short-day breeders’. Thus, photoperiod controls the timing of conceptions in hinds.