Seabirds are full of crap — which turns out to be an important source of nutrients in coastal areas, new research says.

Bird poop, also known as guano, is chock-full of key plant foods like nitrogen and phosphorus — and when seabirds flock together to breed, they can produce massive quantities of the stuff. Every year, more than 1.3 billion pounds of nitrogen (591 million kilograms) and 218 million pounds of phosphorus (99 million kilograms) dribble out of this deluge of droppings, according to a study published this week in the journal Nature Communications.

Knowing exactly how much of these nutrients seabirds pump out can help scientists predict what might change in the environment if the birds were to die out. Plus, there’s an important goldilocks zone for nutrients in bodies of water. Too little, and species that rely on these food sources could have trouble growing. Too much, and you can get dangerous, or at least unpleasant, algal blooms that suck oxygen from the water and kill fish. So it’s key to know where the nitrogen and phosphorus is coming from — and some of it is definitely coming from seabird butts.

“This is really fascinating,” says Scott Winton, an aquatic chemist at ETH Zurich in Switzerland. Winton was not involved in the research, but has studied how seagulls can spread nutrients from landfills to nearby water. “I love stories like this.”

Usually we hear about nitrogen and phosphorus runoff when agriculture or human waste causes too much of it to leak into water, causing dead zones like the one choking the Gulf of Mexico. But it’s also important to understand other sources of nitrogen and phosphorus, like seabirds — which fetch food from the ocean, digest it, and poop it back out on land. Nitrogen and phosphorus in that poop can then leach into the soil, underground reservoirs, rivers and lakes, and the ocean.

So researchers led by Miguel Angel Huerta-Diaz at the Universidad Autónoma de Baja California in Mexico wanted to find out just how much comes from the millions of seabirds worldwide. By calculating how many birds flock to breeding sites, how long different species stay put, and roughly how big the individual birds are, the researchers found that seabirds produce roughly the same amount of nitrogen and phosphorus as the fishing industry.  But not as much nitrogen as, for example, bean farming. (Beans are especially efficient at sucking nitrogen out of the air and pumping it back into soil.) And much more phosphorus leaches out of rocks and sediment than bird poop.  

Still, every source of nutrients could be important for understanding the delicate balance that keeps ecosystems healthy. That’s especially key as scientists try to understand how climate change will affect water quality in the future. And now they have millions and millions of pounds of nutrients from bird poop to add to their models.