Polygynandry is a reproductive strategy that occurs when two or more males have an exclusive sexual relationship with two or more females. The numbers of males and females need not be equal. In vertebrate species studied so far, the number of males usually is in a lower ratio to that of the females in their breeding groups. Some animals follow this behavior regularly, others resort to it in uncharacteristic circumstances.
Polygynandrous groups often will contain related males. The advantage of this form of sexual behavior is greater genetic diversity, less need for males to compete with each other, and greater protection for, and nurturing of, the young. 
The Bicknell thrush is known to be a bird species that practices polygynandry. As many as four males may attend one female and her offspring. The strategy is considered a distinct advantage for the welfare of the young birds of this species, who receive nutritious meals from attentive males who have mated with their mothers. They raise their young on alpine mountaintops in New England and winter in the Dominican Republic, Haiti, and a small portion on the Island of Cuba. Generally, the environment in which these birds breed is threatened. The New England habitats are threatened with rising temperatures via global warming and their typical winter habitats are suffering deforestation.
The Dunnock is known for multiple mating systems, including monogamy, polyandry, polygyny, and polygynandry. In monogamy and polygynandry, neither sex is able to have an advantage over the other in terms of reproductive success.
- Lowman, Meg, Unique bird faces extinction, Sarasota Herald Tribune, page A7, July 23, 2012
- The dictionary definition of polygynandry at Wiktionary
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