Male care for offspring is rather rare in some taxa of species. This is because males may increase their fitness by searching for multiple mates. Females are limited in fitness by their fecundity, so multiple mating does not affect their fitness to the same extent. Males have the opportunity to find a new mate earlier than females when there is internal fertilization or the females exhibit the majority of the care for the offspring. When males are shown to care for offspring as well as females, it is referred to as bi-parental care.