Birds disappearing from America

Why are so many birds vanishing?
23 September 2019

Interview with 

Ken Rosenberg, Cornell University


A black and white image of a flock of birds


Around the world, millions of people have united to campaign for action on climate change. There’s significant concern about what’s happening to the environment and the world’s flora and fauna. And we need to worry, because many species are coming under significant pressure. The birdsong we hear walking through a forest may be replaced with silence. Chris Smith spoke with Ken Rosenberg, wo is at Cornell University in the US where he’s been studying bird populations and habitats, and his latest findings, which have been published in the journal Science, should certainly put the cat among the proverbial pigeons…

Ken - This study is showing a staggering loss in the abundance of birds all around us in North America. We're seeing about a 30 percent loss in the total number of birds out there since 1970. That's a loss of 3 billion birds, which means that our best estimates is that there were about 10 billion breeding birds in 1970, and about 7 billion birds today.

Chris - And if you stratify by all the different species, who are the biggest losers or is everyone the loser here?

Ken - Well we saw large losses in almost every habitat group. The biggest losers are probably grassland and farmland birds, because they showed the largest proportional loss. More than half of their population gone since 1970, and also the largest absolute loss, about 700 million birds from their population was lost. But there were smaller levels of loss in almost every habitat.

Chris - Were there any winners? Did the numbers of any rise to compensate?

Ken - There were. So in North America where most of the conservation investment has been, is in waterfowl and wetland birds. And that showed up in the data. The wetland bird group was the only group to show an increase. Waterfowl populations have more than doubled in that same time period since 1970, and that's because of the investment in wetland restoration, waterfowl management, primarily for recreational hunting.

Chris - I'm intrigued to know how you actually have managed to count three billion birds.

Ken - We used a lot of different survey data sources, because there are so many bird watchers out there we have a lot of eyes and ears, and by organising standardised surveys that use volunteer birders to count birds, 400 species are covered pretty well by this Breeding Bird Survey, and then we brought in other surveys such as the Christmas Bird Count to look at birds that we only see in the winter. So basically we put together the best information we had for each bird group.

Chris - But in the paper you also talk about using radar?

Ken - Right, weather radar gives you a picture of the total mass of birds that are migrating over the continent in any given time, and these birds are flying at night. And so the radar is picking up the total biomass of their migration at night, and by looking at that number over time, so over an 11 year period we saw a reduction in the total biomass of migrating birds. That was about the same magnitude of decline as we were seeing in the survey data. So two completely independent methodologies and data sources were showing the same results.

Chris - What do you think the mechanism underpinning all of this is? Do you think there's one single mechanism or do you think there's a range of factors here?

Ken - There's definitely a range of factors. We have a pretty strong sense that habitat loss and degradation is the primary driver for most groups of birds, but there are many things that kill birds that are human caused, and they range from pesticides, cats, windows, collisions with buildings and towers. There is lots of different drivers, pinning them down to the specific decline of any species is very difficult to do and that's really the next phase of our research.

Chris - I'm very alarmed by the scale of these figures, and not just the scale but how quickly this has kicked in, and the reason for asking the question about what you think the mechanism is, is that well, if we're going to try to arrest that decline, we need to know what's causing it. And it doesn't sound like you've got a clear picture on that yet. So it's going to be really really hard to get a handle on this, and perhaps it's too late already. Would you say?

Ken - Well, I don't think it's too late for most groups, and we do know that bird populations are very resilient, and we have this model from wetland and waterfowl to to guide us. We know that with bald eagles and other raptors, when we saw a problem with DDT and we were able to ban those pesticides, and stop those birds from being shot, their populations did rebound, and so we need to replicate those successes. So in grasslands we need some changes in agricultural policy that allows there to be some native grassland on the habitat, and agriculture has become so intensive that it has just squeezed birds off the landscape, where even 10-20 years ago there were more birds that we were able to live side by side with. So it's going to take a lot of different actions at the individual level, at the societal level. But we are hopeful, but because we know that this has worked in other cases.

Chris - You've got this in North America, but do you think this is, it’s a horrible analogy but the canary in the coal mine for what's going on in geographies worldwide? If I did the same sort of study in Europe, or in Russia, or in Australia, would I see a similar trend?

Ken -  Absolutely and these papers are coming out one after another about declines in birds in Europe, declines of insects globally, this is a global phenomenon. The loss of biodiversity, the loss of species, the loss of abundance, so the canary in the coal mine analogy is exactly correct today. This is telling us that there is something dreadfully wrong in our environment, we can see what's going on with birds because they're so conspicuous and we can count them. So we can be sure that what it's telling us, is that these things are going on with other groups as well and that we're seeing an unraveling of ecosystems and a degradation of the health of our overall environment. It has to be happening if the losses are so pervasive as we're seeing.


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