I've made a few birdhouses recently. The idea of making one that looked like a skull crossed my mind, but I rejected the notion. My reasoning was that birds would instinctively avoid something that resembled a large, and therefore possibly predatory face. It seems I guessed wrongly.

I don't think birds care once they get used to something - esp if there's food around. I like these, they're remeniscent of Mexico's Day Of The Dead festival.

And it looks awesome with the bird shooting out of the eye socket.