JOHN DANKOSKY: Six years after signing the Declaration of Independence, Congress chose the bald eagle as the national bird. Even though Ben Franklin was not a fan, he found the turkey to be a much more respectable bird. The rest of the delegates, however, selected the eagle because of its strength.

Two centuries on, though, the symbol of American independence was nearly wiped out back in the 1960s with under 500 nesting pairs out in the wild. Government agencies had to step in. They eliminated DDT and passing policies like the Endangered Species Act to protect the eagle’s habitat.

One key to conserving the eagle is protecting the nest. But how well does that really work? Well, a study published this week in the Journal of Applied Ecology looked at that question. Here to talk to us about it is Benjamin Zuckerberg. He’s an Associate Professor of Wildlife Ecology at the University of Wisconsin-Madison. Welcome to Science Friday.

BENJAMIN ZUCKERBERG: Thank you for having me.

JOHN DANKOSKY: So tell us, why is the nest such a critical place to focus these conservation efforts?

BENJAMIN ZUCKERBERG: Yeah. So as you kind of mentioned, bald eagles have really suffered pretty widespread declines in the early 1900s. And in the recent decades, they’ve really come roaring back thanks a lot to protection and pesticide bans. And one of the sort of real clear management actions that a lot of agencies have taken is to try and protect the nest.

It’s a very long-lived bird. They can leave almost 25 years in the wild. But they only produce about one or maybe two young. And so trying to protect these nests and seeing whether or not that protection can have sort of population level effects and help recovery is a major initiative for many agencies.

JOHN DANKOSKY: So tell us about how the national parks are protecting these individual bald eagle nests. What exactly are they doing?

BENJAMIN ZUCKERBERG: Yeah. So starting back in the early 1960s, wildlife biologists came up with the idea of these sort of buffer zones. And so the idea here is actually pretty simple. You put up signs and these signs are basically trying to tell the public to stay away, to not disturb the nests.

And bald eagles and other sort of large raptors are very sensitive to human disturbance. Even a camper, or a hiker, or certainly a motorized boat in the area will cause them to flush and in some cases abandon the nest. And so this idea here is to set up these buffer zones that restrict the human disturbance and activity within the nests, and this can be anywhere from 600 feet to about 1,000 feet or so that basically tells people to please stay away and give the nesting eagles some space.

JOHN DANKOSKY: And you looked at how these buffer zones work in one park– Voyageurs National Park in Minnesota. Tell us what you saw there.

BENJAMIN ZUCKERBERG: Yeah. So Voyageurs National Park is in northern Minnesota. It’s a really beautiful park– almost 40% water. It’s got several major lakes and large minor lakes as well. And what we are really interested in was to see whether or not this idea of setting up these buffer zones really helps the population.

And what happened is is that starting in the 1970s or so, wildlife biologists with the National Park Service started monitoring these nests. And it turned into a really wonderful long-term monitoring data set. And what they showed was a very similar story that’s playing out at the national scale– that roughly in sort of the late 1970s and early ’80s that we saw the bald eagle population in Voyageurs National Park start coming back up.

And so there was about 10 breeding pairs or so in those early surveys. And right around the late 1980s, they started seeing an increase in the number of these breeding pairs. But they wanted to help this recovery along. So in 1991, they started setting up these buffer zones.

And what we looked at was that when they actually started setting up these buffer zones around really just a handful of nests– so we’re talking nine, 10, maybe some years 15 nests– that this had an overall positive effect on nest success– so the ability for a pair of eagles to actually successfully produce young from their nests– and also had these population-level effects.

So what we found was that overall there was an 8% increase in nest success in these managed and protected nests. There was a 13% increase overall– and so the ability to produce lots of young to more than two or more young in these nests.

And the nice thing about this, overall, is that during this time period of about 20 years of managing these nests, the breeding pairs went from about 10 or so in the mid to late 1980s to now 48 breeding pairs. And what we show is that just doing this management, which I think is a fairly straightforward type of protection, generally conferred about a 38% increase in that overall population rise.

JOHN DANKOSKY: But it’s so interesting because that sounds so simple, right? Keep people away from the nests and the eagles do better. Is it that simple?

BENJAMIN ZUCKERBERG: I think in some ways it is. I think in many cases what’s interesting about this is that you don’t have to do this for every nests, that because this is a long-lived species that we’re very good about making protected areas, setting up national parks or wildlife areas and sanctuaries. But at the same time, a lot of these recovering predators need additional help. And so just even the act of going in and protecting nests or telling people to stay away from these nests can have really significant benefits over the long term.

And what I think is interesting too is that this is a national park. We’re not talking about building a parking lot or a highway. This is really sort of low-level human disturbance, I think, as many people would think about it. We’re talking about camping, and hiking, and fishing, and recreational boating. But in many cases, even these low-level disturbances can have a real population-level effect on recovering predators.

JOHN DANKOSKY: We’re talking with Ben Zuckerberg about bald eagles. Our phone number is 844-724-8255. If you’ve been seeing eagles come back to your area– it’s 844-SCI-TALK. I’m John Dankosky and this is Science Friday from WNYC Studios.

So this success isn’t just happening at Voyageurs, though. This is more widespread.

BENJAMIN ZUCKERBERG: Oh, yeah. No. It really is one of the great conservation stories for the United States. The bald eagle was listed as part of the Endangered Species Act, And they were given and conferred certain protections. And over time, that has really paid off. The elimination of DDT and as well as habitat protection and these very discreet management activities to try and protect nests definitely have paid off to the point where, as you mentioned, there was only 500 or so breeding pairs in the lower 48 United States, and now we have well over 10,000 pairs. And so we’ve seen this sort of national phenomenon of these top predators, these bald eagles, being able to repatriate some of their former habitats.

JOHN DANKOSKY: Are they basically back to what we would see as a normal population throughout their range, or is there still room to grow?

BENJAMIN ZUCKERBERG: Oh, I think there’s still room to grow. In fact, at Voyageurs, what I would say is that they are still coming in. The population and the number of breeding pairs have not seemed to saturate. So there’s definitely still room to grow in a lot of these areas.

And we do have to keep in mind that it wasn’t just DDT, that back in the early 1900s, bald eagles were actively persecuted. There was actually bounties for bald eagles. And so their populations really are recovering from what has been more than 100 years of persecution, environmental pollution, and habitat loss.

JOHN DANKOSKY: Well, what’s interesting about these buffer zones is that in national parks you can protect and you can space out maybe 1,000 feet so people aren’t coming near them. But I’ve got to say, Ben, I drive down a road almost every day of my life and bald eagles fly overhead. There are nests that I can see. They seem to be adapting pretty well to living near humans.

BENJAMIN ZUCKERBERG: Yeah. And that’s a really interesting question is whether or not they can habituate over time. What I would say is that not only if they are potentially using a nest, it doesn’t necessarily mean that they are being successful in raising young in that nest. And so even though they may be setting up a nest in a certain area, whether or not that nest is ultimately successful– and certainly what we hope to have a really highly productive nest, meaning that they are raising two or more young– and that’s really the goal of a lot of what we think about in terms of conservation and management is to optimize that reproduction– it doesn’t necessarily mean, even if you see a bald eagle nesting in an area, that that nest ends up being successful.

But I would say you’re absolutely right, that a lot of species and a lot of returning predators– not just bald eagles, but other species as well– are certainly beginning to adapt to what are increasingly human-modified landscapes.

JOHN DANKOSKY: We’re running low on time. I just want to ask you quickly, what is a bald eagle being back in the ecosystem mean for the ecosystem around it?

BENJAMIN ZUCKERBERG: That’s a fantastic question. And I think that’s our next suite of questions is that you have what was effectively a top predator that was removed from its natural system and ecosystem and is now returning to that system and what are the other consequences it might have for even other recovering species as well? And I think that question is still outstanding.

But it clearly is a possibility, especially for bald eagles. They do certainly affect other birds of prey, like ospreys and even great blue herons. They’ll take other birds’ food. They’ll even predate on adults. And so we are actively thinking about that next step of what are these other trophic-level consequences.

JOHN DANKOSKY: And I’m sure you get this question all the time. But we started off by talking about Ben Franklin. Look, if the turkey was the national bird, would people have cared enough about the bald eagle to save it in the way that they have been, do you think?

BENJAMIN ZUCKERBERG: I think so in the sense that it is a real flagship species, meaning that it is clearly a charismatic species. It’s a beautiful bird. It’s got this wonderful, large wingspan and this bright white head. And so I think it always captures people’s imagination. And so when you’ve got a species like this that is just a beautiful emblem of nature, I think it’s always going to engender imagination and people’s interest in conservation.

JOHN DANKOSKY: Benjamin Zuckerberg is an Associate Professor of Wildlife Ecology at the University of Wisconsin-Madison. Benjamin, thanks so much for your study and thanks for coming on Science Friday with us. I really appreciate it.

BENJAMIN ZUCKERBERG: Thank you.

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