I doubt I’m the first person to ask this, but a search of the archives has revealed nothing. Could someone enlighten me?
Thanking you and grovelling in admiration,
Alice
It’s not poo. It’s urine. But if you look closely, the teeny, tiny dark speck in the middle is the poo.
Actually, the white part is composed of urates; bird urine tends to be clear and watery.
The missing ingredient here is something rather obvious: a bird has an all-purpose butthole, or cloaca. It all comes out at once.
Birds and reptiles do not pee like we do- they excrete liquid waste in mainly crystalline form, called urates. They do not produce uric acid, which is the main component of human urine. This system is thought to have evolved as a way to control water loss, since the chalky urates contain far less water than human urine. But they do release some waste water- just not much.
Not only does it limit water loss, but it’s a major boon for egg layers. Urates are generally inert nitrgoenous wastes, whereas urine (as excreted by mammals) has a significant ammonia component; the buildup of ammonia within an enclosed egg would be fatal to the developing embryo.
Stay tuned to the Straight Dope Home Page. In the next week or two there should be a Staff Report by Colibri that addresses this very question.