Frank Landis sent the following letter
(response sent from mail@cartalk.com).
In reply to the question about whether car color attracts bird droppings, I don't have a car (really), but I do have a pet pigeon (really). This bird is actually a really fun pet that flies around my apartment, so I know something about his (as we biologists say) excretory behavior.
For one thing, you have to realize something about bird butts. Most flying birds don't have strong rectal muscles--they can't hold it in very long. Why should they? They'd have to carry all that crap around while they're flying, and it's a lot cheaper just to get rid of it. This is why you can't potty train most birds. This does not mean, though, that they can't let go whenever they want to, and some of them have very good aim.
Although I've never read anything about this, two years of watching my pet pigeon has convinced me that he marks his favorite perches with droppings. Whenever I clean one of these places, he immediately comes over and marks it again.
Think about it for a second--bird droppings are mostly black and white, which make an excellent visual marker in the natural world. And birds, of course, are visual creatures. So far as I know, nobody's tested this idea, but it certainly makes sense.
Now, for the implications: If birds (esp. pigeons) mark their territory, that explains why it's so hard to keep certain public statues clean. If you clean off the birds' turf markings, they immediately have to reapply them, or they lose their territory. Second, think about what car color looks like most like a bird dropping. That's right, a white car. So a white car comes across as a monster territorial marker, and any bird around will rush to claim it. That's why a white car will attract more droppings.
It makes a good story, anyway.
Cheers,
Frank Landis
