Birds are often reputed to be "monogamous." Is that true? At Salon, Jed Lipinski discussed the topic with Bernd Heinrich, a renowned naturalist at the University of Vermont, who has recently written "The Nesting Season: Cuckoos, Cuckolds, and the Invention of Monogamy." Here's an small excerpt from a larger discussion that touches upon monogamy, "love," navigation and other topics:

Monogamy among birds is mostly social monogamy, in that they will pair off, but they won’t necessarily be sexually monogamous. Some of them are, of course, but most try not to be, as there are certain advantages to being not monogamous. Monogamy is often forced upon birds because of certain conditions. Mates might be scarce, say, and it's safer to have a mate around. Or a female needs a mate to keep the offspring alive, to make sure all the courting and mating and nesting hasn’t been a big waste. It takes a lot of resources and help to raise baby birds -- so the parents have to have a lot of investment. Social monogamy works for food and protection, especially in the case of geese or birds of prey. So no, most birds are not monogamous. But monogamy is relative. It differs not only between species but within species as well, and often according to gender. Male birds of paradise are extremely promiscuous, whereas the females are extremely picky. They may only mate once in a breeding cycle, while a male will mate with hundreds of females and at any time. But then there are precocious birds, like ducks and quail, whose females manage to do all the feeding themselves, so a male isn't really required. . . . And some birds are not at all polyamorous. Ravens, for example, stay in pairs year round. That's unusual.