As a child I had a very limited knowledge on birds. This was probably because I was busy learning about trees from my father who is a forester. My first recollection of learning about birds was from my dad’s experience traveling around Madagascar in crowded buses. Long rides around the country always resulted in the much needed bathroom breaks along the way. From this came the common saying, people aren’t chickens (or birds), meaning unlike birds we need to pee.
This didn’t make any sense until my father explained that birds don’t urinate. Ok, so birds don’t urinate, but how is that possible. This is where my birding course comes in. It has helped me to understand a lot more about the physiology of birds.
A basic difference between humans and birds is that while birds have combined two digestive channels into one, mammals have two separate channels that function for defecation and excretion. While for birds, defecation and excretion comes out as solid waste, for humans there is separate liquid and solid waste. It all comes down to how birds and humans make use of water in their bodies.
Birds are much more efficient with their water retention. To preserve water and because of their high metabolism rates, birds use a different method for excretion. While humans make use of water to dissolve their metabolic wastes, birds don’t dissolve their nitrogenous urea waste in water, but rather dispel a nitrogenous uric acid. This is what is commonly noticed as the white paste seen all over rocks. This is clearly visible in the set of images below.
Just a few images of birds on the Farne Islands in North Cumberland, England
On the other hand, birds’ defecation waste matter is a darker black. This is solid food waste. Interestingly enough, the need for defecation is not something that all birds have. This is especially true for sea birds, like the ones seen in the images above (Cormorants, Puffins, Terns, etc…). These birds almost completely digest all of their food (fish) and therefore only excrete the white waste matter.