Anatomy: Excretion

Any visit to a crow roost focuses one’s mind on the subject of bird poop.  How do I to avoid it? Will it stain? Do they time this so they’ll hit me?   So in today’s anatomy lesson I’m skipping over the next logical topic in bird digestion and jumping directly to the back end.  Hold on to your hats!

Unlike mammals, birds have a single opening for both urinary and digestive excretions so their poop is made of two components: output from their kidneys and from their intestines.

Birds’ kidneys are a miracle of water conservation.  Instead of passing urea and water their kidneys produce uric acid, a white, crystalline, semi-solid that’s not water soluble and is full of nitrogen.  This makes it a good fertilizer that’s easy to collect because it doesn’t wash away.

If you were on the receiving end of bird poop and it was only made of uric acid, it wouldn’t immediately stain your clothes.  You could probably scrape it off.  Unfortunately the second component of bird poop — digestive waste — is disgusting and it can stain.  Pokeberries make purple marks no matter whether you daub them on your clothes yourself or receive a little “gift” from a bird.  Need I say more?

You may not have noticed, but birds poop just before they fly to lighten their load.  I sometimes amaze my friends by remarking, “That hawk is about to take off,” and then it does.  They don’t know I just saw it poop.

Some people think birds are aiming for them.  “Do they time this so they’ll hit me?”  Not exactly.  If you stand below a flock of birds and give them the creeps they’ll get ready to fly.  When they lighten their load you might get hit, but they weren’t aiming for you.

Which brings me full circle to the crow roost and a word to the wise:  The absolute worst time of day to be on the ground under the roost is just when the flock disperses at dawn.

Wear a hat.  Better yet, wear a rain slicker and carry an umbrella.


(photo of the Ruskin Avenue sidewalk below the crow roost, by Kate St. John)

4 thoughts on “Anatomy: Excretion

  1. Kate, I was driving on the parkway toward downtown last night and saw a huge flock of crows fly over near Churchill. Do you know if this is the same group that roosts in Oakland, or are there multiple sites in Pittsburgh?

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