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Why is bird poo white?

Sent in by John Martin Lamberty, near Lewes, East Sussex

Firstly, it is not actually the bird poo that is white, it is uric acid which is the bird equivalent to human's urine. Without going into too much technical detail, it is white due to the chemical reactions that occur within the urinary system to process the waste matter into a substance that can be safely excreted with minimal water loss.

Birds excrete waste products from the urinary and digestive tract at the same time through what is known as the vent after passing through an organ known as the cloaca. Because they are expelled at the same time but from different systems, they do not have time to mix which explains why bird mess usually consists of distinct coloured and white parts.

However, certain foods such as elderberries may alter the colour of birds excretia as the colour of the fruit persists throughout the digestive process.

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