Why is poo brown and why is it white in birds?
In mammals the haemoglobin in red cells is broken down into bilirubin, which is processed by the body and excreted as stercobilin in the faeces (making them brown) and to a lesser extent, as urobilinogen in the urine (making it yellow). As for birds – they don’t excrete nitrogen waste as urea like we do, but as uric acid. In mammals the urea is accompanied by a load of water, producing urine. In birds, less fluid is needed to excrete the uric acid, so you get a small amount of white paste or fluid. This makes up the white component of bird droppings. The dark bit is the digested food matter, the equivalent of faeces. They both are excreted out the same opening.
