In the wood frog all females in some populations are receptive for just one night a year. Males are so pressed for time that they do not defend territories but instead rush around trying to encounter as many receptive females as possible. Horseshoe crabs also have scramble competition polygyny B. Monogamy. Monagamy may occur when potential for polygyny is so reduced by the scarcity of females that a female, having found a potential mate can gain more by guarding her than by trying to find additional mates Male shrimp Hymenocera picta, stay monogamous with female because females are rare and hard to find and only mate about every 3 weeks after they molt. So male finding female stays with her and repels other males, mating when possible with his female.
More birds are socially monogamous than any other group.
Birds need biparental care of the young which increases reproductive success of males that provide care. Birds with synchronized breeding seasons are especially monogamous. After courtship, the number of unpaired females for males is small. Females with males that provide some parental care may try to enforce monogamy by not pairing with already paired male, or by trying to chase off any additional females from their male. Value of male assistance in the snow bunting.