Monogamy is the practice of mating with the same individual for an extended period of time. It turns out only about 3% of animals in the animal kingdom are actually monogamous. Researchers used to think that birds were one of the most monogamous creatures, with some staying with one mate for life. However, new studies have shown that birds are very good at cheating. For example, while Superb Fairywrens appear to be monogamous for life, a fertile female will take pre-dawn flights to other territories. Upon genetic testing of her offspring, only about 25% are from her supposed lifetime mate.
Scientists looked into why monogamy is not as common in other species. Sticking with birds as an example, monogamy is helpful to both parents in that their young need a lot of time and care to help grow. Two birds are better than one. However, phenotypic traits of birds are various and distinct. If the birds put all of their genetics into one nest, their genetics might not continue if that nest fails. If a bird shares its genetics among different nests, its evolutionary traits are more likely to survive. For some animals that have shorter lifespans, this can be advantageous to evolution of survival.