When it comes to excretions, birds do a two-for-one deal
Do birds pee? In a word, no. Birds are creatures of the air and therefore need to stay as light as possible. Among their myriad adaptations to do so is the design of their excretory system.
Producing pee as well as poo, as we mammals do, means you’re going to be retaining urine (which consists of nitrogen-rich urea diluted with lots of water) in a bladder. This isn’t very helpful if you are trying to keep your weight down.
So, instead of excreting waste matter as both urine and faeces, birds (with the exception of the ostrich) ditch their waste in one go through an opening called the cloaca. They don’t have bladders, nor urethral openings.
This waste product is highly concentrated uric acid – the white paste that regularly splats all over our windows, patios and cars. It doesn’t dissolve in water easily, hence its ability to cling on like a blob of plaster.
If humans do number ones and number twos, you could say that birds do number threes. And if three is the magic number, no wonder it’s considered lucky when a bird splat lands directly in our hair.
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