Purple Poop

Dear Madame L,

We have noticed bird droppings on the bottom steps of our front porch. It wasn't bad when they were just little white droppings, but now there are big purple splotchy stains on the steps, mixed in with the droppings. I looked up, and, sure enough, there is a nest in the branch that hangs over that place. 

At first I thought the birds had purple poop, but now I realize that there is probably a nestful of baby birds, and the parents are probably feeding their babies mulberries or some other purple berry. Just like human babies who are learning to eat solids, those baby birds are messy eaters! 

I don't know where there are any mulberry trees in my neighborhood, but these splotches look a lot like the splotches I've seen on the sidewalks under mulberry trees before. My question is: what birds do you know of that feed their babies mulberries? Or do you think I'm way off and maybe those birds really do have purple poop?

Sign Me,

Occasional Birdwatcher and Purple Poop Cleaner-Upper

Dear Poop Cleaner,

Ah, Madame L feels your pain! It's bad enough having to clean up bird poop, but when it's purple, it's more than twice as bad, isn't it.

(And Madame L apologizes for taking so long to respond to your question.)

Purple bird poop is, as you suspected, the result of birds eating mulberries --- and/or any other red, blue, black, or purple berries, or pomegranates. And you're right that it's poop, not just messes of berry mash that the nestlings didn't eat carefully.

(You probably noticed the poop still has that whitish pasty bit, uric acid mixed with a small amount of water, which is how birds get rid of urea, the end result of their bodies' nitrogen cycle.) 

Just about every kind of bird that lives in the vicinity of mulberry trees feeds these berries to their babies. The birds also enjoy the mulberry trees for shade, shelter, and building nests. 

Patience, Dear Reader,

Madame L