Researchers found that about 25 percent of the black rosy-finch hatchlings found in this and two other nests were not sired by the male feeding and guarding them—proof that the female had not been monogamous.
Blood samples were taken from the nestlings and the male parent and then using microsatellite DNA fingerprinting—a method used to determine paternity in animals—researchers determined that the samples suggested the female had been visiting neighboring males for sneaky copulations.
This behavior was supported by samples later taken from other black rosy-finch nests, with around 25 percent of chicks sired by males other than the female's nesting mate. For the first time this bracketed female rosy-finches with a range of other birds, from flamingoes to sparrows, that also "play" away from home. Read more from National Geographic.