Why is bird poo white?

30 May 2010

Question

Hi Naked Scientists, 

I was seating with a cup of coffee on a chair in my back yard in the morning, watching a seagull flying above me, wondering if I'd have the time to avoid it's poo, if the seagull felt such a need right above me.  And then I remembered my car, and the fact that the birds' excrements were white. What kind of things happen in their body to make their excrements white, whilst they are eating about the same things as other animals eat?

Many thanks,

Adrian

Answer

Helen - Excellent question and it's not actually anything to do with what they eat which is one thing you could think of - well maybe they eat something that's white? but no. They eat just the same stuff as all sorts of other creatures, but it's about how they process that food and it's all about proteins and nucleic acids, and how they break that down. We break down proteins and we all produce ammonia, but we make it into urea which we then dissolve in water and get rid of it in urine. But we need lots of water to do that, so that means we have to drink a lot which means we don't really survive very well when there's not much water around.

Birds and reptiles have a better way of dealing perhaps with low water, and the need to get rid of all that nasty toxic ammonia, and they create something called uric acid which is a solid or a mostly solid paste. That is white, and that's why their poo is white. In fact, it's very valuable stuff. Guano has been mined in lots of parts of the world to be used as fertiliser and wars have been fought over it because it can be used to make gunpowder - it's got very high nitrogen and phosphorus in it. So, there you go - white bird poo has lots of rather extraordinary applications.

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