A Troubling Decline In North American Birds

11:59 minutes

a lone bird calling out perched on a beam of wood
A meadowlark, one of the species that saw its population drastically decline in the past decades. Credit: Shutterstock

There may be almost 3 billion fewer birds in North America today than there were in 1970, according to a study published this week in the journal Science. Researchers combined data collected over time from projects such as the North American Breeding Bird Survey, the Audubon Christmas Bird Count, and the International Shorebird Survey to make their calculations, which looked at 529 species in the continental US and Canada. They also looked at observations of nighttime bird migration flight captured on NEXRAD radar systems. 

The decline in North American bird populations over time works out to a loss of about one in 4 birds. However, the decline does not appear to be evenly distributed—most of the drop-off observed by the researchers is attributed to just 12 species, including some sparrows and warblers. The researchers observed gains in the populations of other birds, mainly raptors and waterfowl species.

Ken Rosenberg, one of the authors of the study and a senior scientist at the Cornell Lab of Ornithology and American Bird Conservancy, joins Ira to talk about the study, possible reasons for the decline, and things that average people can do to help preserve and protect bird species.

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Segment Guests

Ken Rosenberg

Ken Rosenberg is an applied conservation scientist at the Cornell Lab of Ornithology in Ithaca, New York.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. We’ve heard about steep declines in the populations of certain species. For instance, just this February, reports of a drop in insect populations worldwide. Now another possible warning sign of global environment in crisis.

A report in the journal Science this week says that North American bird populations have declined by nearly 3 billion– that’s with a B– 3 billion birds since 1970. That’s a loss of nearly one in four birds. What is the cause, and how do you count that kind of population decline?

Ken Rosenberg is one of the authors of that report and an applied conservation scientist at the famous Cornell Lab of Ornithology in Ithaca. Welcome back to Science Friday.

KEN ROSENBERG: Thanks. Hi, Ira.

IRA FLATOW: That’s a lot of birds. Isn’t it?

KEN ROSENBERG: It is a lot of birds. There are a lot of birds out there. But we’ve been seeing this steady decline, and people who love birds and are out there every day have been noticing fewer and fewer birds. And now we can put some hard numbers on those declines.

IRA FLATOW: But there’s still a lot of birds left, right? We’re not talking about an extinction here.

KEN ROSENBERG: We’re not and this is different from other studies that are showing. And of course, there are birds that are dropping towards extinction. But what we’re seeing here is like a whole other level of biodiversity loss because we’re seeing the loss of abundance among common species of birds. So it’s not just the rare and threatened species. But what we’re finding is this pervasive loss among common familiar everyday birds.

IRA FLATOW: Give me an idea of what we’re talking about, what kind of birds.

KEN ROSENBERG: Well, some of the biggest losses are in grassland birds, birds like meadowlarks and horned larks, savanna sparrows. But not only the specialist species, one of the big surprising results is that other birds that are found out in farmland rural landscapes across America, like red winged blackbirds, are also in steep decline. So what that’s telling us is that habitat loss is so pervasive and that these environments are just not able to support basic bird life.

IRA FLATOW: We have had birds go extinct. I’m speaking specifically about the famous passenger pigeon, right?

KEN ROSENBERG: That’s right, and we make an analogy in the paper. One of our co-authors had done this fascinating study where she was able to bring in whatever data existed from the passenger pigeon from the 1800s and essentially create a model of what the decline of the passenger pigeon might have looked like before it went extinct.

And that decline looked a lot like what we’re seeing today in these other common birds. And nobody ever thought the passenger pigeon would go extinct. It was the most abundant bird that ever lived on the continent. But these declines look very similar. And what it’s telling us is that if we had been monitoring birds back at that time and people were paying attention, and we were at that 30% loss point, let’s say, it’s very likely that we would have been able to prevent that extinction and do something about it.

IRA FLATOW: And is that the same case now? Can we prevent any loss of birds?

KEN ROSENBERG: Well, we might not be able to save everything, but that is what gives us hope. And we have examples of birds more recently that we have recovered and that we have brought back– the bald eagle, the peregrine falcon. In those cases, we knew what the problem was when we were able to ban DDT, the harmful pesticide, and pass laws that stopped shooting of hawks and eagles. And these populations rebounded pretty quickly. So we know birds can be resilient. We know that they will respond positively to our actions if we do it.

IRA FLATOW: But don’t we have to know why they died off to begin with?

KEN ROSENBERG: That’s true. And we maybe got lucky, in a sense, with the bald eagle because DDT was such an obvious factor. And since these losses we’re seeing now are so pervasive– they’re really across every single habitat– then obviously, multiple factors are at work. And it’s very complex, and it’s not a simple thing.

But we do know in a lot of cases what the major factors are in habitat loss, and we know a lot of the things that are killing birds, such as collisions with windows and buildings, and predation by outdoor cats. And these are things that we can do something about, and we can minimize those bird deaths at the same time that we’re working to protect and restore habitat.

IRA FLATOW: Is changing climate have anything to do with this, you think?

KEN ROSENBERG: Well, that’s a good question this week, of course, and we’ve thought about that a lot. And climate change is obviously having an effect, and it’s probably going to be having more of an effect as we move forward.

But climate change is not the driver of these big declines. It is habitat loss. And so in a sense, the habitat loss issue is it’s right in front of us. There’s so much urgency there, and if we’re not protecting and restoring habitats and if there isn’t enough habitat for these birds to survive in and move– and not just birds, other wildlife to move into, as climate change does whatever it’s going to do on the landscape, then it won’t matter very much. So we can’t just focus on climate change into the future. We have to make sure we’re protecting these populations right now.

IRA FLATOW: Let me get a bit into the methodology. This is fascinating to me– I hope to my listeners, too. How do you know? How do you count the bird populations?

KEN ROSENBERG: Well, we relied on two very independent sources of data. And one of them were fairly simple counts that have gone back 50 years or more that are done by bird watchers. And because so many people love birds and can identify them, we have this fantastic collaboration between the scientists and the amateur bird watchers, where the scientists can design these surveys that are quite rigorous.

But the bird watchers are the eyes and the ears out there. Scientists cannot collect this kind of data themselves. So we have thousands of people out there collecting the data and then giving it back to the scientists, who can then do these analyses. And so we’re very lucky to have this 50 year monitoring data set on bird populations. We don’t have anything like that for any other group of organisms.

But then the weather radar data was a completely different source. It doesn’t rely on human observations. And radar can see the migration that’s happening in the sky. And since most birds are actually migrating at night, the radar is picking up these bird migrations at night. You could even see this on the Weather Channel. If you see a big storm coming on when they show the radar, that clutter that you see out behind the storm, those are birds usually.


KEN ROSENBERG: So the weather people filter that out, but ornithologists have taken advantage of it. And it’s really only recently, because we need supercomputers, really, to look at it at that scale. There are 143 of these next rad weather radar stations, and we’re able to piece that together and look at the total mass of migration that’s passing over the United States over the entire spring migration.

And we went back in time with that kind of data. We were able to go back only 11 years. But we saw a 14% decline in the mass of migration passing over the United States in just an 11 year period. And that’s about the same order of magnitude that we were seeing from the surveys. So these two very independent sources of data are essentially telling us there’s this major loss, and that gives us a lot more confidence that the result is real.

IRA FLATOW: Do you have any confidence that folks like us, the individual, can do anything to help?

KEN ROSENBERG: Well, it’s going to start with the individual, just as your previous guest was talking about, and if we’re going to solve the climate crisis. The response to this paper has really been phenomenal. There is so much interest in this story because so many people love birds.

And we’ve provided a list of actions that people can do. And we have a sheet called the Seven Simple Actions, and I’m not sure I can remember all seven of them. But they are things like protecting your windows and preventing birds from crashing into your windows by breaking up the reflection and keeping your cat indoors, so it doesn’t hunt birds. And drinking bird friendly coffee is a great simple way. It’s great coffee, and you could be saving bird habitat at the same time.

IRA FLATOW: I guess, stop there for a minute and tell me what bird friendly coffee is. I’d like to get some.

KEN ROSENBERG: Well, most coffee, all coffee, is grown in tropical regions. And like a lot of other agricultural crops, to grow coffee normally requires cutting down the rainforest. But in certain areas, they grow the coffee underneath the shade of the rainforest canopy. And it serves to protect the habitat, but it produces great coffee.

And it’s a small proportion of the market right now. But it’s something that we’re trying to make people aware of and make them grow. Make that grow. So it’s shade grown coffee that we consider to be friendly to birds.

IRA FLATOW: What about pesticides? Do they kill off the birds?

KEN ROSENBERG: Well, they certainly do, and since so many of the declines we’re seeing are birds associated with agricultural areas in one way or another, on top of the outright loss of habitat, you have this greater and greater use of more toxic pesticides. These neo nicotinoids could be worse than DDT, and a different study just came out this week in Science as well, showing the high toxicity of these chemicals to birds.

And we think that this could be the cause of declines in certain groups of birds, such as these aerial and insect eating birds, aerial insectivores such as swallows, and swifts, and nighthawks that have been declining so steeply. So absolutely, that’s part of the puzzle.

And then minimizing your use of pesticides around your home is a good start. Every one of these individual actions can then be amplified by taking it to scale in your community. And ultimately, we want people who are doing these things to be a voice for change, so that these can actually result in changed policies and societal change.

IRA FLATOW: You mentioned in your list that pollinators were a problem. Tell me what you mean by that.

KEN ROSENBERG: Pollinator’s a problem. Well, birds are such an integral part of all ecosystems, and they perform these services as part of the ecosystems. And they act as predators and prey in the food webs, but birds are also doing things like pollination. They’re doing pest control of insects. They’re doing dispersal of seeds. They’re helping forests regenerate by dispersing seeds.

So when you’re losing this big chunk of bird abundance, you’re losing those functions within the ecosystems. And we could be approaching a point where the ecosystems themselves are unraveling.

IRA FLATOW: Another tipping point to be fearful of, OK.

KEN ROSENBERG: Yeah, well, it could be happening. It’s hard not to be alarmist when you have numbers like we’ve generated here.

IRA FLATOW: Now we’ve all read Silent Spring, so we know what could be happening. Ken Rosenberg is the author of a report in Science and applied conservation scientist at the Cornell Lab of Ornithology in Ithaca, New York. Thank you for taking time to be with us today.

KEN ROSENBERG: Thank you, Ira.

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About Charles Bergquist

As Science Friday’s director and senior producer, Charles Bergquist channels the chaos of a live production studio into something sounding like a radio program. Favorite topics include planetary sciences, chemistry, materials, and shiny things with blinking lights.

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Ira Flatow is the host and executive producer of Science FridayHis green thumb has revived many an office plant at death’s door.

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