Yes, folks, birds and crocs can pee

January 28, 2016

ostrich peeing

cormorant peeing

alligator peeing

Stand by . . . grumpy old man routine compiling . . . 

So, someone at Sony decided that an Angry Birds movie would be a good idea, about three years after the Angry Birds “having a moment” moment was over. There’s a trailer for it now, and at the end of the trailer, a bird pees for like 17 seconds (which is about 1/7 of my personal record, but whatever).

And now I see these Poindexters all over the internet pushing their glasses up their noses and typing, “But everyone knows that birds don’t pee! They make uric acid instead! That’s the white stuff in ‘bird poop’. Dur-hur-hur-hurrr!” I am reasonably sure these are the same people who harped on the “inaccuracy” of the peeing Postosuchus in Walking With Dinosaurs two decades ago. (Honestly, how I didn’t get this written and posted in our first year of blogging is quite beyond my capacity.)

Congratulations, IFLScientists, on knowing One Fact about nature. Tragically for you, nature knows countless facts, and among them are that birds and crocodilians can pee. And since extant dinosaurs can and do pee, extinct ones probably could as well.

So, you know . . . try to show a little respect.

So, you know . . . try to show a little respect.

Now, it is true that crocs (mostly) and birds (always?) release more of their nitrogenous waste as uric acid than as urea. But their bodies produce both compounds. So does yours. We mammals are just shifted waaaay more heavily toward urea than uric acid, and extant archosaurs – and many (but not all) other reptiles to boot – are shifted waaaay more heavily toward uric acid than urea. Alligators also make a crapload of ammonia, but that’s a story for another time.

BUT, crucially, birds and crocs almost always release some clear, watery, urea-containing fluid when they dump the whitish uric acid, as shown in this helpful diagram that I stole from International Cockatiel Resource:

International Cockatiel Resource bird pee guide

If you’ve never seen this, you’re just not getting to the bird poop fast enough – the urine is drying up before you notice it. Pick up the pace!

Sometimes birds and crocs save up a large quantity of fluid, and then flush everything out of their cloacas and lower intestines in one shot, as shown in the photos dribbled through this post. Which has led to some erroneous reports that ostriches have urinary bladders. They don’t, they just back up lots of urine into their colons. Many birds recapture some water and minerals that way, and thereby concentrate their wastes and save water – basically using the colon as a sort of second-stage kidney (Skadhauge 1976).

Rhea peeing by Markus Buhler

Many thanks to Markus Bühler for permission to post his well-timed u-rhea photo.

[UPDATE the next day: To be perfectly clear, all that’s going on here is that the birds and crocs keep their cloacal sphincters closed. The kidneys keep on producing urine and uric acid, and with no way out (closed sphincter) and nowhere else to go (no bladder – although urinary bladders have evolved repeatedly in lizards), the pee backs up into the colon. So if you’re wondering if extinct dinosaurs needed some kind of special adaptation to be able to pee, the answer is no. Peeing is an inherent possibility, and in fact the default setting, for any reptile that can keep its cloaca shut.]

Aaaanyway, all those white urate solids tend to make bird pee more whitish than yellow, as shown in the photos. I have seen a photo of an ostrich making a good solid stream from cloaca to ground that was yellow, but that was years ago and frustratingly I haven’t been able to relocate it. Crocodilians seem to have no problem making a clear, yellowish pee-stream, as you can see in many hilarious YouTube videos of gators peeing on herpetologists and reporters, which I am putting at the bottom of this post so as not to break up the flow of the rant.

ostrich excreting

You can explore this “secret history” of archosaur pee by entering the appropriate search terms into Google Scholar, where you’ll find papers with titles like:

  • “Technique for the collection of clear urine from the Nile crocodile (Crocodylus niloticus)” (Myburgh et al. 2012)
  • “Movement of urine in the lower colon and cloaca of ostriches” (Duke et al. 1995)
  • “Plasma homeostasis and cloacal urine composition in Crocodylus porosus caught along a salinity gradient” (Grigg 1981)
  • “Cloacal absorption of urine in birds” (Skadhauge 1976)
  • “The cloacal storage of urine in the rooster” (Skadhauge 1968)

I’ve helpfully highlighted the operative term, to reinforce the main point of the post. Many of these papers are freely available – get the links from the References section below. A few are paywalled – really, Elsevier? $31.50 for a half-century-old paper on chicken pee? – but I’m saving them up, and I’ll be happy to lend a hand to other scholars who want to follow this stream of inquiry. If you’re really into the physiology of birds pooling pee in their poopers, the work of Erik Skadhauge will be a gold mine.

Now, to be fair, I seriously doubt that any bird has ever peed for 17 seconds. But the misinformation abroad on the net seems to be more about whether birds and other archosaurs can pee at all, rather than whether a normal amount of bird pee was exaggerated for comedic effect in the Angry Birds trailer.

ostrich excreting 3

In conclusion, birds and crocs can pee. Go tell the world.

And now, those gator peeing videos I promised:


Jan. 30, 2016: I just became aware that I had missed one of the best previous discussions of this topic, with one of the best videos, and the most relevant citations! The post is this one, by Brian Switek, which went up almost two years ago, the video is this excellent shot of an ostrich urinating and then defecating immediately after:

…and the citations are McCarville and Bishop (2002) – an SVP poster about a possible sauropod pee-scour, which is knew about but didn’t mention yet because I was saving it for a post of its own – and Fernandes et al. (2004) on some very convincing trace fossils of dinosaurs peeing on sand, from the Lower Cretaceous of Brazil. In addition to being cogent and well-illustrated, the Fernandes et al. paper has the lovely attribute of being freely available, here.

So, sorry, Brian, that I’d missed your post!

And for everyone else, stand by for another dinosaur pee post soon. And here’s one more video of an ostrich urinating (not pooping as the video title implies). The main event starts about 45 seconds in.


17 Responses to “Yes, folks, birds and crocs can pee”

  1. Frosted Flake Says:

    Generally, (gosh, I hope I am not called to a account upon this), the time it takes a fellow to pee and his weight seem to have a relationship.

  2. Frosted Flake Says:

    No suggestion that it might be OK for police to shoot dogs.

  3. gunnarmk Says:

    Challenging internet truisms? Urine big trouble.

  4. dasypus Says:

    Brilliant post. What annoys me more than the fair-weather pseudo-pedants is the fact that Fox News ran a segment on the dangers of alligator attacks.

  5. Matt Wedel Says:

    Generally, (gosh, I hope I am not called to a account upon this), the time it takes a fellow to pee and his weight seem to have a relationship.

    Fittingly, I was holding it on a very long drive to a dinosaur dig, and as a young, n00b grad student, I didn’t want to be the one to suggest that we stop the truck. By the end I was seriously using almost all of my conscious brain power to keep from peeing my pants. As with so many things about my early 20s, I look back now and wonder what the hell I was thinking.

  6. Aha! I could have sworn that I saw an emu peeing once in a zoo in Rome twenty years ago, but everything I’ve read since then convinced me that such a thing was not possible. Vindication!

  7. Mike Taylor Says:

    So that‘s what happened to your conscious brain power!

  8. […] remember that in the last installment (before Matt got distrated and wrote about archosaur urine), I proposed a general schema for aggregating scores in several metrics, terming the result an LWM […]

  9. Mark Robinson Says:

    Great post. In real life I’ve seen a freshwater crocodile urinate and I’ve also seen close-up both emus (twice) and an ostrich do that cloacal evacuation thing where the excreted material contained a lot of liquid.

    However, I was unclear (unlike the urine) on whether the liquid was considered to be urine as I didn’t know whether that term was reserved only for liquid that had passed thru a bladder. So thanks for reducing the turbidity for me.

    Also, if you wear adult nappies, you can direct all that conscious brain power toward important stuff such as thinking about sauropods.

  10. Matt Wedel Says:

    Thanks for the kind words, and for helping me optimize my productivity. Sounds like ureally have seen some cool stuff.

    Once liquid leaves the kidneys, it’s fair to call it urine, even if goes through a round or three of cloacal uptake and concentration.

    Glad I could distill this stuff for you.

  11. Mark Robinson Says:

    Haha. Touché!

    Thanks for clarifying.

  12. Bolko Says:

    Crocodilians are a different story from birds, as they are mostly aquatic and aren’t under selective pressure to concentrate thier urine. Also, do birds finally have sphincters? Popular sites tell that birds do not have sphincters, and so they poop everywhere. I would not be surprised if I learnt that mostly aerial species have this configuration, but what about more terrestrial ones?

  13. […] Birds can and do urinate: here’s a rhea doing just that. Photo by Markus Bühler, taken from the famous SVPOW article Yes, folks, birds and crocs can pee. […]

  14. Jules Akers Says:

    Correcting obscure misconceptions: good. Going on with yourself like a dick, like you just won the Correct Olympics or something: less good. Enjoyed the gator/ostrich pissing videos though.

  15. Matt Wedel Says:

    All fair! Even though I only got bronze in the Correct Olympics. Glad you enjoyed the post.

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