Can Bird Poop Make Clouds?

  • By Anna Rothschild
  • Posted 01.05.17
  • NOVA

Bird poop could help clouds form, keeping our planet a little bit cooler. Discover how in this episode of Gross Science.

Running Time: 03:49


Can Bird Poop Make Clouds?

Posted: January 5, 2017

Do you see a fluffy white cloud in the sky? Depending where you are, it could be made of bird poop—well...kind of.

I’m Anna and this is Gross Science.

To understand how bird poop could make clouds, you first need to know a little something about how clouds form. So, clouds form when water evaporates from ocean, lakes, and other reservoirs, or is released from plants in a process called transpiration. This water is in a gaseous form, called water vapor, and it floats up into the atmosphere. Now, the vapor could just hang out in the air unseen. But in order to become a cloud, the water has to cool and attach itself to something we call a “condensation nucleus.” Dust particles, ice crystals, specks of pollution, and even fungal spores can all serve as “condensation nuclei.” Water molecules glom onto them, becoming water droplets—and when this is repeated over and over again, we can see these droplets in the form of clouds.

So, what does this have to do with bird poop? Well, bird poop is really rich in nitrogen. And we’ve known this for years. Beginning centuries ago, people would actually mine guano—which is a fancy term for the accumulated poop or seabirds or bats—and they’d use it as fertilizer, because nitrogen helps plants grow. But, humans aren’t the only creatures with an affection for guano. Bacteria love it, too.

Bacteria chow down on the guano, and release another nitrogen-based molecule, called ammonia, as a waste product. And given that tens of millions of seabirds spend their summers in the Arctic, bacteria there produce a ton of ammonia—about 40,000 metric tons each year, to be exact.

When the ammonia drifts up into the atmosphere, it reacts with sulfuric acid and water. And when other molecules in the air latch on it becomes a condensation nucleus—adding to the total number of these guys floating around above the Arctic.

Now, you know how clouds can either look bright or dark? Well, that’s due to the size and number of droplets they’re made of. Here are two clouds, each in an environment with the same amount of water vapor in the atmosphere. The bright one is made of a large number of small droplets, while the dark one is made of a small number of large droplets. In the bright cloud, the water’s just divided among more condensation nuclei.

Now, there’s still a lot we don’t understand about how clouds affect climate, but we do know that bright clouds help reflect sunlight away from Earth, which means that they can have a cooling effect on our planet. And that means that all the additional droplets contributed by the ammonia from Arctic bird poop could be helping to keep our planet a little bit cooler. The effects are likely not huge. But as Greg Wentworth, a scientist involved with the study, told me, the birds make a “relatively small, yet smelly, contribution.”

For me, this study brings home the importance of basic research. Both on clouds, but also on seabird biology. Now that that we know bird poop may be part of our climate story, it’s more important than ever for us to study and protect them. So, all you future scientists out there—I hope you’re feeling inspired. And maybe just a little grossed out.




Host, Writer, Animator, Editor
Anna Rothschild
Camera, Sound
Janet DeFilippo
Plucky Little Thing
Music Provided by APM
Many thanks to Dr. Greg Wentworth


Bird Photography Outtakes
Flickr/Ingrid Taylor
Monterey a rock with bird+their crap
Wikimedia Commons/Mrmariokartguy
Bagged Quano & Trolly
Wikimedia Commons/J.R. Mann
Grímsey puffins
Flickr/Jennifer Boyer
Guillemots on Bear Island Svalbard Arctic
Flickr/Gary Bembridge
Wikimedia Commons/Henning Allmers,


(used with permission from author)
Squeak Pack/squeak_10
Slide Whistle Down 01
Slide Whistle Up 01
Produced by WGBH for PBS Digital Studios


Want more info?

(Primary Literature) Contribution of Arctic seabird-colony ammonia to atmospheric particles and cloud-albedo radiative effect:

Science News article on bird poop and clouds:

NASA on bright and dark clouds:

Related Links