Compared to polgyny (in which males mate with more than one female per breeding season), polyandry is not as common.
In birds, polyandry is divided into two main forms: 1) cooperative polyandry, in which several males defend a female’s territory and mate with her and 2) resource defense polyandry, in which females defend territories that contain smaller areas of groups of males. Cooperative polyandry occurs among The Galapagos hawk, as females will mate with up to seven different males during the mating season. Throughout the nesting period, the female and her multiple male partners take turns incubating the eggs and feeding the offspring. Wattled jacana females display resource defense polyandry, mating with multiple males on her territory and laying clutches of eggs within intervals of less than two weeks.
Polyandry also occurs in other species. In social insects for example, a single queen will sometimes mate with many males. Interestingly, polyandrous nests often have greater levels of conflict because each group that belongs to a different genetic line may compete with one another for greater representation in the next generation.
Depending on the species and situation, a polyandrous mating strategy may offer four main benefits to females: 1) sperm replenishment – females add to depleted or low sperm supply and avoid the cost of storing sperm; 2) material benefits – females receive additional nutrients and protection from other males; 3) genetic benefits – offspring of females will have more varied genes (which will help some survive in a dynamic environment); and 4) convenience – females avoid the costs of searching for and fending off unwanted mates.
When polyandry and polygyny are occurring in the same population, the breeding system is described as promiscuous. Among Barbary macaques, for example, both males and females mate repeatedly in rapid succession. Polygynandry, is a special type of promiscuous mating system in which multiple pair bonds are formed. Researchers have documented instances in which pairs of male dunnocks (small bird common in Europe and Asia) will defend the territory of a pair of female dunnocks.
No matter the mating system of choice, for many species, it is often diverse and complex.