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Asked by iqwaaaaa to Emma, Jimmy, Janet, Niall, Simon on 18 Mar 2013.
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Emma Ashley answered on 18 Mar 2013:
Because birds don’t urinate, the kidneys that usually excrete a waste product uric acid in urine instead excrete it into the poo. This causes the poo to be both white and it also has some black in it sometimes too (that is the waste product of bilirubin – a compound that is produced when you break down you red blood cells).
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James Holloway answered on 18 Mar 2013:
Mammals create urea as a waste product, it is quite a nasty chemical so our bodies mix it with lots of water to keep it safe while it is in our bodies.
Birds however, can’t afford to have lots of extra water to mix it with because water is heavy, and they need to fly. So instead they make a different less nasty chemical so they don’t need all that water (this does cost them extra energy though).
Fish are different still. Fish have all the water they could possible need so actually make ammonia instead of urea. This is an even nastier chemical to have in your body but its ok because the fish can dilute it with all the water they need, and they save energy along the way!
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