No it isn't...and I didn't say it was. The fact that we do that shows that nature takes a back seat to humanity when we want it to.
Put it like this: homosexuality in nature is just an excuse and justification for people to engage in ANY sexual behavior they may have thought was once wrong, but since they WANT to do it, they use the "nature" argument.
That argument is stopped cold as regards the millions of other things that happen in nature that we arbitrarily condemn, and the reason is that it harms others -- I have no issue with that, personally. But my overall point is that homosexual acts are not controlled by nature, they're simply controlled by our desires, so we make excuses to do it...but since we're intelligent enough to control our murderous, cannibalistic nature, why does that not also apply to sexual activity, is my question.
Now, if you want to argue that sexual reproduction is a primary facet of nature, then I'd counter that gays don't "reproduce" together....they just have sex.