Think Out Loud

Double-crested cormorants create conundrum for biologists

By Allison Frost (OPB)
Nov. 20, 2023 2 p.m.

Broadcast: Monday, Nov. 20

Three cormorants on East Sand Island

Three cormorants on East Sand Island

Vince Patton


The double-crested cormorant is one of many seabirds that love to eat salmon. Many of the birds were driven away from East Sand Island near the mouth of the Columbia River decades ago in an effort to protect the fish, but wildlife managers are now responding to some unintended consequences. Roughly 10,000 cormorants now prefer to make their home on the Astoria-Megler Bridge. The acid from their excrement, or guano, eats through the bridge coating which Oregon Department of Transportation workers must remove regularly for safety inspections. Nesting cormorants can also find their way onto the roadway, leading to encounters which can be fatal for the birds and pose safety hazards for drivers. We talk with James Lawonn, an avian biologist at the Oregon Department of Fish & Wildlife, about what’s being done to protect the birds and the bridge.

Note: The following transcript was created by a computer and edited by a volunteer.

Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. The double-crested cormorant is one of many seabirds that love to eat salmon. The birds were driven away from East Sand Island near the mouth of the Columbia River starting in 2015 in an effort to protect the fish. That’s led to some unintended consequences. Roughly 10,000 cormorants now nest on the Astoria-Megler Bridge. So many that the acid from their poop is corroding the bridge’s coating. That guano has to be removed regularly by the Oregon Department of Transportation, plus nesting cormorants sometimes find their way onto the roadway, which can be fatal for them and dangerous for drivers.

James Lawonn is an avian biologist at the Oregon Department of Fish and Wildlife. He joins us to talk about what’s being done to protect birds and the bridge. Good to have you on the show.

James Lawonn: Thanks for having me.

Miller: Before we get to the bridge and efforts to move these birds once already, can you just describe the birds we’re talking about: what is a double-crested cormorant?

Lawonn:  Sure, a double-crested cormorant is a sort of nondescript goose-sized bird. They are often described as being sort of eerie or otherworldly or gothic looking.

Miller: Why is that?

Lawonn: Well, they kind of give the impression of looking like a gargoyle a little bit. They often will perch and they’ll have their wings outspread and they look a little bit like the batman symbol when they do that. So they definitely give an impression of sort of a mysterious kind of bird.

Miller: Goose-sized. So, this is a pretty good sized bird.

Lawonn: Yeah, small goose, they weigh about four pounds.

Miller: What’s their favorite food?

Lawonn: Well, they’re pretty generalist in their diet. They generally eat fish, and they are pretty non-picky about it. They’re opportunistic feeders. So, basically, whatever is around and is easy for them to catch.

Miller: And when salmon are around, that means they’ll eat salmon.

Lawonn: Sure. Yeah, definitely.

Miller: When did humans around here start saying that salmon predation by cormorants was a big enough problem that something had to be done about the cormorants?

Lawonn: Well, research really started in the late 1990′s, which is about the same time that the double-crested cormorant population in the Columbia River Estuary really started to increase. And researchers, knowing that cormorants have some pretty high energy requirements – they eat about a pound to a pound and a half of fish per day – and just doing some math, researchers thought, “Huh? I wonder what kind of effects they’re having on salmon and steelhead.”

Miller: And this was at a time when questions about salmon populations had been huge issues well before then, but just getting worse and worse by the 90′s and going onwards. So what were the thoughts, early on, about what to do about this?

Lawonn: Well, there were a lot of different thoughts throughout the years. I mean, researchers throughout the 90′s and early 2000′s really got a handle on what kind of impacts cormorants – and by cormorants, I’m talking about double-crested cormorants, again – were having on various runs of salmon and steelhead.

There are 13 different runs of salmon and steelhead that are listed under the Endangered Species Act. Some of those runs were just starting to be listed in the late 90′s. And so researchers gradually learned that, “Hey, this is potentially an issue. What can we do to reduce cormorant predation on these fish?”

And the plan that you had mentioned just a few minutes ago was really spearheaded by the Army Corps of Engineers. The idea was to reduce the overall number of cormorants on East Sand Island, and by doing that, reduce the overall number of cormorants in the estuary. And by doing that, you reduce impacts on salmon and steelhead.

Miller: And so, we’ll talk about what they actually did to get the birds to move. But in the grand scheme of things, how do cormorants compare to hydroelectric dams or ocean conditions or spawning habitat in rivers that are getting warmer, say. There’s a lot of reasons that salmon numbers are down. Where do cormorants fit in the larger picture?

Lawonn: Sure. I’m glad you asked that question. So, cormorants are not really an original cause of declines of salmon and steelhead in the Columbia River basin. When we’re thinking about the primary factors involved with conservation issues for salmon and steelhead, we’re thinking about the dams, we’re thinking about habitat, and those are really the major drivers. However, cormorants do consume on the order of between 7% to maybe even 12% of available steelhead, for example, that have already made it past all the dams to the estuary. So it’s not small potatoes. It’s not nearly the scale as these bigger issues related to dams and habitats, but still appreciable.

Miller: So what did people do at East Sand Island to get these cormorants to move on?

Lawonn: The idea behind that plan was to reduce the number by culling cormorants. So basically shooting cormorants as well as by spraying vegetable oil on their nests, and that would essentially smother the eggs. So the idea was you could actually reduce the size of the colony by removing cormorants from the local population.

Miller: And it worked?

Lawonn: It worked and it didn’t work. So the number of cormorants in the estuary did in fact decline. Today, there are about 5,500 double-crested cormorants across the entire estuary, compared to an average of around 13,000 during the heyday of the East Sand Island colony in the 2000′s and 2010′s. But the main goal of this management was to reduce impacts by cormorants on salmon and steelhead. And that actually didn’t happen and it didn’t happen because some cormorants, about four to five thousand breeding pairs -10,000 or so individuals - moved to the Astoria Megler Bridge, which is really close to East Sand Island. It’s only eight miles away.

Miller: They said, “If you’re gonna kill us here, we’ll go somewhere else.”


Lawonn: Yeah, cormorants are like a lot of seabirds. They’re really looking for a safe colony site to nest…

Miller: Like all of us.

Lawonn: Like all of us, right? And in retrospect, it was pretty obvious that double crested-cormorants found that East Sand Island was a pretty dangerous place for them to be, and it just so happens only eight miles away, which is nothing for a cormorant, there was already a colony present. A small colony, there were a few hundred breeding pairs on the Astoria Megler Bridge then, in 2015. But cormorants would have seen those birds doing quite well at that colony site.

Miller: In terms of the impact on salmon, is there any difference between a cormorant eating salmon or steelhead at the old place they were - the island - versus eight miles upriver, at the bridge. Is it the same, essentially?

Lawonn: Well, actually not really. And this is the really interesting thing - the fish communities in the estuary are different, depending on where you are in the estuary.  East Sand Island is located really close to the mouth of the Columbia River, and that’s what we call the marine zone of the estuary. So the water there is essentially just like an extension of the ocean. It’s very salty and there’s all kinds of marine forage fish, like anchovies or shiner perch that are present there.

Miller: As if it’s the ocean.

Lawonn: Right. So the fish community there is like the ocean. When you go farther up river, you have fewer of those marine fish because the water salinity is different. And so you have a different fish community. So near the Astoria Megler Bridge, when a cormorant is searching for food, it’s much more likely to come across a juvenile salmon or steelhead than an anchovy, for example. And as a result, cormorants’ diet includes more of these endangered and threatened salmon and steelhead.

Miller: So, it seems the effort backfired in a number of ways. I mean, it’s bad for the bridge, which we’ll talk about in just a second, and they’re more likely to be in a place where they could do more damage in terms of salmon populations.

Lawonn: Yeah, there are several issues with cormorants on the bridge and the issues with salmon and steelhead are no joke. We think that the 4,000 breeding pairs of cormorants on the bridge are having the same or even a slightly greater impact than the former colony on East Sand Island that again supported around 13,000 breeding pairs.

Miller: All right, let’s turn to what their guano means. Why is it such bad news for the bridge itself?

Lawonn: Without doing a detailed chemical analysis of it, it’s bad stuff because basically, it accelerates corrosion of the very expensive and costly to put on coating that [the] Oregon Department of Transportation puts over the metal portions of the bridge. And so this guano, essentially it whitewashes areas of the bridge that the Oregon Department of Transportation needs to inspect biennially, just to make sure that the bridge is in shipshape.

Miller: So not only is it eating away at the coating, which is there to preserve the life of the bridge and to prevent the metal from oxidizing, whatever. But there’s so much of it that the inspectors can’t even see what the bridge looks like. They can’t see what they need to inspect.

Lawonn: It’s much less efficient for the inspectors. They do have to clear nests and remove guano just to see what they need to see. But even then it does increase the risk that the inspectors might not see some of the smaller imperfections in the bridge that will eventually need repair. And so what ends up happening is that repairs need to be done, by the time repairs do occur there, the defects of the bridge are already large enough where it’s just more expensive to fix. And so this is one reason that cormorants on the bridge are quite expensive for the Oregon Department of Transportation.

Miller: And what about road safety? I mean, how common is it

for the birds to actually end up on the roadway itself?

Lawonn: Yeah, and this is a big bummer, both for cormorants and for potential... It’s just a bummer situation. Cormorants nest in some areas of the bridge immediately below the roadway, like a yard underneath the road. And what ends up happening is birds that are ready to fledge - essentially baby cormorants - are just big enough to start using their wings, end up on the roadway and they get hit by vehicles and during some times of the year we’re seeing 10 or so cormorants hit every day.

Miller: Wow.

Lawonn: So it’s pretty significant and these birds are fairly good size. They’re the size of a small goose and they potentially could cause a traffic accident as well. So, not a good situation.

Miller: What is the plan right now to fix the situation?

Lawonn: The region, and by the region I mean Oregon Department of Fish and Wildlife and our partners, we’re thinking of a plan that will push double-crested cormorants away from East Sand Island using non-lethal means, basically scaring them, and at the same time pulling them back to East Sand Island. And remember we’re talking about a much smaller number of cormorants, only 4,000 or so breeding pairs. And so this combination of a push from the bridge and a pull back to East Sand Island, we think could be successful at moving this very large colony.

Miller: But that was exactly what the Army Corps of Engineers tried to prevent. I mean, why go back to this island that the Army Corps thought was a bad place for cormorants to be?

Lawonn: Sure, that’s a great question, right? The big point here is that we’re talking about a much smaller number of cormorants, and that the goal would be to manage a much smaller colony. So over the short term, it would be however many birds are driven from the bridge, which would probably be around 4,000 breeding pairs. And just moving the colony from the bridge to East Sand Island would, we think, reduce predation rates by cormorants by 75% or more.

Miller: Because they’d be eating other fish?

Lawonn: They’d be eating other fish. That’s right.

Miller: Do you imagine a day when these birds don’t have to be managed, when there is a kind of status quo that is sustainable?

Lawonn: Ideally, that would be the case. One thing to point out, though, is that the Columbia River Estuary is a really attractive place, not only for double crested cormorants but for waterbirds in general. And the reason is there’s just so much food there. And so it’s possible that some level of management could be necessary in perpetuity, and that management might just be scaring cormorants from the bridge every once in a while when they try to set up there again.

Miller: With loud noises?

Lawonn: The idea would be loud noises, or even excluding birds from parts of the bridge using netting or other techniques.

Miller: James Lawonn, Thanks very much.

Lawonn: Thank you.

Miller: James Lawonn is an avian biologist with the Oregon Department of Fish and Wildlife. He joined us to talk about what to do with cormorants who are now nesting in pretty large numbers on the Astoria Megler Bridge.

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