Whatever their reason is, we found these window decals that are supposed to work like a bright stoplight for the birds. We just put them up yesterday so we don't know how effective they are yet, though they do have great reviews!
From their website:
"...The decal contains a component which brilliantly reflects ultraviolet sunlight. This ultraviolet light is invisible to humans, but glows like a stoplight for birds."
We bought the maple leaf shapes.
And here's one of our crazy little backyard doves with our always-hungry backyard bunny (sorry for the poor picture quality). I'm not quite sure what this strange duo was up to, but I'm pretty sure this is what Mr. Dove was saying: