I'll Never Think of Donald the Same Way Again

I never, ever would have thought that I'd see reference to a duck, the Dutch, homosexuality, and necrophelia all in the same sentence. I could maybe see the last three going together, but the addition of a duck is what really threw me. Thanks to Daypop's top 40, I stumbled onto this article talking about the odd sexual behavior of ducks, mainly homosexuality, rape, and necrophelia. Check out the opening quote of the article

The strange case of the homosexual necrophiliac duck pushed out the boundaries of knowledge in a rather improbable way when it was recorded by Dutch researcher Kees Moeliker.

In my studies of sociobiology, I'd read a lot of research on the proliferation of homosexual tendencies in certain animals. I'd also read about some cases of rape being an acceptable form of reproduction, but I never ran across a study that found an animal to be necrophilic. Necrophilia doesn't serve any type of positive advantage for reproduction so why hasn't it slowly evolved out of the duck population? There must be some positive to it for it to still be present, right?

I suppose that by having sex with dead ducks, a male is getting some practice in for the real thing, but that might be stretching it. Maybe when ducks have sex the female lies there like she's asleep and the necrophilic ducks have sex with dead ducks because they think of them as sleeping females. I don't really know how ducks have sex, so I'm not sure if this is even close to how things really are.

So why do ducks have sex with dead ducks? I'm drawing a blank here.