Extracting and analyzing DNA from the feathers confirmed that not a single eagle had strayed from its mate during the course of the six-year study - a degree of monogamy unusual among birds.This is a common misuse of the term monogamy. The article confuses monogamy with fidelity.
Biologists once believed that most, if not all, bird species were monogamous. But over the past decade, that presumption, based on observations of apparently faithful male-female pairs building nests and raising young together, has been overturned by genetic "paternity tests" of blood samples from the birds.
In more than 75 percent of avian species looked at so far, researchers have discovered broods that have two or more fathers.
Monogamy means marriage. In animals, it refers to mating for life. Many animals, such as a lot of birds, form pair bonds for life but are not necessarily sexually faithful to each other. If they form a permanent pair bond, then they are monogamous.
Humans can also be monogamous and promiscuous at the same time. If they stay married, then they are monogamous. In some marriages, sexual fidelity is extremely important, and in other marriages, it is not so important.