We Need To Talk About Bird Poop

12:04 minutes

nine black colored birds sitting on white guano-stained rock with ocean in the background
A colony of Guanay Cormorants on the coast of Peru, a threatened species of seabird. Credit: Shutterstock

Seabird poop—sometimes called guano—was the “white gold” of fertilizers for humans for millennia. Rich in nitrogen and phosphorus from birds’ fish-based diets, the substance shaped trade routes and powered economies until chemical fertilizers replaced it. 

But while people may no longer find bird poop profitable, these same poop deposits—often found on islands or coasts where the birds nest and rear their young—may also be nurturing ecosystems that would be left high and dry if the birds were to disappear. As seabird populations quickly decline, that’s becoming an increasing risk. 

Australian researchers Megan Grant and Jennifer Lavers talk to Ira about the under-appreciated role of bird guano in ecosystems, and why scientists should be looking more closely at the poop patterns of endangered seabirds.

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Segment Guests

Megan Grant

Megan Grant is a PhD candidate at the University of Tasmania, and is a researcher at Adrift Lab.

Jennifer Lavers

Jennifer Lavers is a senior lecturer of marine sciences at the University of Tasmania, and is a co-director at Adrift Lab.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, we’ll discuss the dino docuseries Prehistoric Planet that comes out next week on AppleTV+. But first, every coastline has his birds. And where there are birds, there is, of course, bird poop. And if you live near a beach, you know this well, whether ducking what may fall from a flying gull or observing the distinctive white color and those offshore rocks.

This bird poop, or guano, white gold as it was once called, was used by people for millennia to fertilize crops. That’s because it’s rich in nitrogen and phosphorus, key nutrients for plant growth. And seabirds leave it, well, everywhere, but especially in the places where they build nesting colonies during the breeding season. Seabirds continue to shape and potentially enrich their ecosystems on coastlines and islands around the world. So what happens if the seabirds are at risk of extinction?

Here with more about what we know about the important role of seabird guano and what we still need to know are my guests Megan Grant, a PhD candidate at the University of Tasmania and a researcher at the Adrift Lab in Australia, and Dr. Jennifer Lavers, senior lecturer in marine sciences, also at the Adrift Lab. Welcome both of you to Science Friday.


MEGAN GRANT: Thank you for having us, Ira.

IRA FLATOW: Nice to have you. Megan, why did you decide to research seabird guano in the first place?

MEGAN GRANT: I suppose it’s not the sexy topic, but I think it’s really interesting because seabirds are so integral to terrestrial environments. It’s quite unique in that they move nutrients from the marine environment to terrestrial environments. And that form of movement doesn’t happen very often. Most of the nutrients flow from terrestrial areas to marine environments, not the other way around. So seabirds are incredibly important.

And seabirds have been suggested as the most important vector, or transport mechanism, for the movement of nutrients out of any animal on Earth.

IRA FLATOW: Tell us about this incredible island. Introduce us to that area you study.

MEGAN GRANT: Yeah, so I work out on Lord Howe Island, which is located roughly halfway between New Zealand and Australia. It’s a tropical island with roughly 300 residents living on it, and it’s home to thousands of terrestrial birds, as well as seabirds. And one of these species is the flesh-footed shearwater. You may know it as a mutton bird.

These birds come to Lord Howe Island and breed. So rather than being a surface nester, like say a gull, they burrow into the ground. And their burrows can be two to three meters long, which is incredible for such a small bird.


MEGAN GRANT: I mean, it’s incredible considering that they dig these burrows with their feet. It’s crazy to think.

IRA FLATOW: No kidding, that is crazy.

MEGAN GRANT: These birds come to Lord Howe Island to breed. Then they fly back up to the Sea of Japan, so in the northern hemisphere, forage there, and live there, and then come back to Lord Howe Island to breed.

IRA FLATOW: Now, I mentioned all the nutrients in bird guano. Do we have clues that the flesh-footed shearwater is fertilizing Lord Howe Island with all its guano?

MEGAN GRANT: Absolutely, yeah, so the vegetation structure in the shearwater colonies is predominantly palm species. And it’s this one species of palm called the Kentia palm. There’s very few other species. It’s pretty much 95% palm tree. And then if you walk to the edge of the colony and then step out of the colony, the vegetation structure changes almost immediately.

All of a sudden, you get a variety of shrubs and other tree species and other palm species.


MEGAN GRANT: Yeah, so it seems like there’s this really intricate link between the shearwaters and the vegetation on Lord Howe Island. And that’s where this idea that the shearwaters are bringing really beneficial nutrients to the island. And these areas, these colonies, where the shearwaters are, the vegetation needs the nutrients from their guano to survive.

IRA FLATOW: So that’s the connection–

MEGAN GRANT: Yeah, that’s the connection.

IRA FLATOW: Palm trees and the guano. Interesting. Jennifer, what are some other places where we might be able to notice this connection between seabirds and their ecosystems?

JENNIFER LAVERS: Virtually everywhere we look, really. This is the fascinating thing about seabird colonies. Once we see this or we become aware of their ability to kind of drive their habitats, or be what we call ecosystem engineers, which is quite a cool term, then we’ll start to recognize this pattern everywhere we look. And the vegetation that occurs where those seabirds nest essentially evolves, or adapts, to the response of the birds being present.

And so you get this really intimate relationship, as Megan said, between bird and tree. And only certain trees exist where the birds are. And in the case of the shearwaters and the mutton birds that we’re studying on Lord Howe Island, they are also what we call turbatinng, or turning over, the soil, as they dig their burrows over and over again and basically making a big mess of the place. And so that turning over the soil and that constant depositing of these nutrients really dictates what can grow there and what can’t.

There’s a really great, although I suppose a little bit sad, example from the Aleutian Islands in Alaska. It’s probably one of the better ones that we know of, where in the early 19th century, we introduced foxes as part of the pelt, or the fur trade. And the foxes, in very short order, removed the seabirds, basically ate them for lunch and dinner. And the seabirds were gone. And so what we noticed for the vegetation, the habitat structure, on these Aleutian Islands in Alaska was that they very quickly transitioned from being woody and shrubby and having trees and things to now those islands are grasslands.

And so that was one of the most marked, or clearly demonstrated, examples of if you remove seabirds from these habitats, those habitats just don’t look the way they used to look anymore because they’re not getting the things that they need to maintain the trees and other life.

IRA FLATOW: And Meghan?

MEGAN GRANT: So part of my PhD is looking at how the shearwater guano links very closely to not just the Kent palms that I was talking about, but also to the soil and the soil invertebrates, as well, within these regions of the shearwaters breed. For the soil invertebrates, I’m studying a invasive species, which is the leopard slug, to see whether they also have similar nutrient levels to, say, the guano that the shearwaters have deposited.

But this can be said for seabird colonies all around the world. It’s not just the vegetation that the seabirds influence. It’s the soil, and it’s the soil invertebrates. I can’t remember the exact location, but there was an island somewhere where there were seabird, and they compared it to an island without seabirds. And the island with seabirds, the iguanas were longer than the iguanas on the island without seabirds. So there are huge flow on effects from having seabirds in a region, compared to without seabirds. It’s phenomenal.

IRA FLATOW: So that brings me to this question. We’re talking so much about what we do know. Megan or Jennifer, what do we still need to know?

JENNIFER LAVERS: Well, I’m just thinking of your wonderful review paper that you just did, Megan, and it really pinpointed to us that there are, I’ll say, a handful, maybe a dozen, seabird species that Megan was able to identify that are endangered, or critically endangered. Some of those are known to have been quite heavily involved in the historical guano trade. So we know that there were significant quantities of guano in the past, so much so that our original human societies were based around harvesting of that guano and transporting it around the globe when using it as fertilizer and various kinds of things.

And those seabird populations are now numerically far less abundant, to the point where they’ve been listed as you know vulnerable or endangered. And when Meghan was looking at what do we know about these species with regards to their guano and their population sizes now, and various aspects, the answer was not enough. So we’ve lost a lot of these birds. We clearly have the potential to lose significant amounts of guano with that.

And yet, simple things, very basic metrics like how much nutrients is actually in the guano of that species, so what exactly have we lost, or what could we regain if we restore these vulnerable and endangered species, we couldn’t really answer that question because basic measurements of the value of their guano just aren’t available.

IRA FLATOW: And Megan?

MEGAN GRANT: I was going to say a very similar thing in that I think it’s really important to start studying the species that we could possibly lose.

IRA FLATOW: Megan, I understand that perhaps you can tell people how important seabirds are. Are you consulting on a video game about guano?

MEGAN GRANT: So this is just– when my review paper was published, I put it up on Twitter, just to basically say, look, I’ve written a paper, please go and read it and all of that. And then I had someone comment on that post and said oh, we’re making a board game about guano. We would love to ask you some questions. P.s., this is not a joke. And I didn’t know whether to take this person seriously because even though they said p.s., it’s not a joke, it sounded like a joke.

I mean, who makes a bold game about guano? And basically, they’re making a game a board game about the guano trade when guano was a hot commodity, basically. And in some instances, it was valued more highly than gold. Anyway, so they’re making a board game about this, and they’ve asked me to be their scientific consultant, which is super exciting.



IRA FLATOW: Will you let us know when that game is out?

MEGAN GRANT: It’s coming out next year. So I can’t give away too many details because it’s still in production.

IRA FLATOW: OK, I get it. I get it. Hush hush for now.

MEGAN GRANT: Yeah, exactly.

IRA FLATOW: Well, we’ll have you back when it comes out, OK?

MEGAN GRANT: Absolutely, yeah.

IRA FLATOW: Thank you both for taking time to be with us today.

MEGAN GRANT: Oh, thank you so much for having us. It’s been an absolute joy.

JENNIFER LAVERS: It was wonderful talking about poo all morning.

IRA FLATOW: Any excuse. Meghan Grant, a PhD candidate at the University of Tasmania and researcher at the Adrift Lab in Australia, and Dr. Jennifer Lavers, senior lecturer in marine sciences, also at the Adrift Lab.

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