Female seasonal breeders will have one or more oestrous cycles only when she is "in season" or fertile At this time she is naturally ready to mate. At other times of the year they are not sexually interested. Male seasonal breeders may have changes in testosterone levels, testes weight, and fertility depending on the time of year. For example, male greater sage-grouse actually gain weight as their bodies get ready for the spring breeding season. Seasonal breeders are different than opportunistic breeders. These are species which mate whenever conditions allow it. They are also different from continuous breeders like humans that mate year-round.