The Top 5 Threats to Bird Populations

The worlds' bird populations face many threats. Here I discuss the five biggest threats to vulnerable birds, as identified by BirdLife International.

October 19, 2020
Ivan Phillipsen

I just turned 44 years old. I was born in 1976.

Let’s say you were born a few years earlier, in 1970. You’d be turning 50 this year, in 2020. Congratulations and Happy Birthday!

However, I’m sorry to say that you and I share an unsettling truth: In the last 50 years, in your lifetime and a bit more than my lifetime, North America has suffered a net loss of 30% of its birds. In other words, the total number of individual birds on this continent is only two-thirds of what it was just 50 years ago. That's 3 billion birds wiped out. 

And this was at the hands of humans. There’s nothing natural about these declines.

To clarify, I’m not talking about the loss or extinctions of whole species here, but rather of individuals. Bird populations are getting smaller and smaller. If these declines continue, the end result may indeed be extinction for some or many species.

This sobering statistic comes from an October 2019 study published in the journal Science. This study revealed that many species in North America have declined—not just the rare ones, but also some species we consider common. Yes, some species are stable and a few even have growing populations. But the overall trend is downward for our birds.

This isn’t happening only in North America, and it isn’t just birds. The World Wildlife Federation recently reported that global wildlife populations have declined almost 70% in the last 50 years, since 1970. This has happened in less than one human lifetime. 

Absolute insanity. What will be left in another 50 years?

How did this happen? What are the causes?

Well, that’s what we’re going to talk about today, in terms of what’s happening to birds.

Because before we can decide what we can do to help birds, it’s important to understand why they need help. We need to understand the many threats they face.

Birds are in Trouble

There are about 10,000 bird species in the world. Some authorities put the number at more like 11,000. In any case, the number is in that ballpark, and this means birds are an incredibly diverse group of animals.

But current research tells us that worldwide 40% of these species are in decline. The populations of almost 4,000 bird species are shrinking. And one out of every eight species is threatened with extinction. We don’t have data for all birds, so these numbers are likely underestimates.

So birds are in trouble. Not just in North America, but all across the planet.

Not surprisingly, these declines are not happening to all birds uniformly. Some bird groups are declining faster than others. For one reason or another, some types of birds are being hit harder. 

For example, almost one third of all parrot species is in decline. The situation is worse for Old-world vultures, with 68% of species in decline. And that number is up to 73% for cranes.

How do we know this is happening? Where are these statistics coming from? 

I’m drawing a lot of my information from a report published in 2018 by BirdLife International. It’s called the State of the World’s Birds

BirdLife International conducts and coordinates research on bird conservation. This organization then provides data to the IUCN, which stands for the International Union for the Conservation of Nature. The IUCN is the global authority on the status of wildlife, including birds and all the other critters, as well as plants and fungi. It maintains the Red List of Threatened Species, which provides an evaluation for each species and assigns it to 1 of 9 categories.

Some examples: the Okinawa Woodpecker and the California Condor are both in the “Critically Endangered” category. The Galapagos Penguin and White Cockatoo are in the “Endangered” category. And the Harpy Eagle and Yellow-billed Loon are categorized as “Near Threatened.”

When we talk about trends and statistics from sources like BirdLife International, the IUCN, the World Wildlife Fund, etc., we are really talking about the combined efforts of hundreds or thousands of individual biologists, conservation workers, and government officials.

According to the 2018 report from BirdLife International, 13% of all birds—which is 1,469 species by their reckoning—are globally threatened with extinction. These are the species that the IUCN Red List places in either the “critically endangered,” “endangered,” or “vulnerable” category.

As I talk about threats to birds, I’m mostly referring to the things that pose the greatest danger to the 13% of species that are already in major trouble.

We could easily lose these species forever. For a long time now, humans have been wiping out bird species like it’s our job. It’s estimated that humans drove thousands of bird species to extinction before the year 1500. 

Scientific records became more reliable after 1500. So we know that we’ve lost about 190 species since then. Species like the Dodo, the Passenger Pigeon, and the Great Auk. But there are surely other birds that went extinct since 1500 without us knowing, without us having the hard data.

I won’t go into more detail regarding bird extinctions right now. I’ll save that for another day.

Let’s get to the major threats facing our world’s birds.

What are the top threats to Birds?

Here’s a little quiz:

What do you think are the top three threats that birds face?

Think about it for a moment. Meanwhile, I’m going to throw out a few possible answers.

Pollution. The spread of cities and industry. Massive wildfires. The Illegal pet trade. Disease. Climate change.

All of these would be reasonable answers. You probably came up with some other possibilities.

Before I get to the answer to our quiz, we need to do some clarifying.

When we say “threats,” we’re talking about the causes of bird declines. The things that have and continue to make life unnaturally hard for birds.

So let’s talk about the difference between two types of causes: proximate and ultimate.

A proximate cause is the thing or event that is immediately responsible for whatever result we’re talking about. But, if we trace the chain of events backwards in time, we can often find the ultimate cause. This is the real culprit, the thing or event that really set things in motion to bring about our result of interest.

For example, let’s say you get thrown in jail. We might say the proximate cause is that you robbed a liquor store. 

But if we look back, we might find that you robbed the store because you needed money to buy more birdseed for your backyard feeder. I mean, those birds gotta eat, right? 

You didn’t have money because you don’t have a job because you spend all your time making a podcast about birds. So maybe the ultimate cause for why you're now in jail is that your parents failed to raise a person who understands that it’s possible to both have a job and produce a podcast about birds. Difficult, but possible.

(PssstI produce a podcast about birds.)

We’re looking for the causes of bird declines, the ongoing threats. There are a bunch of these proximate causes, and we’ll examine them in a moment. They’re what this blog post is about. I’d say they’re ultimately what this article is about, but that would be confusing. So forget I said that.

We can trace pretty much any of these proximate causes back to one ultimate cause: human overconsumption combined with human overpopulation.

Okay, that’s actually two ultimate causes, I know, but you get the idea.

Human population went from 3.7 billion in 1970 to 7.8 billion today. That’s more than double in just 50 years! 

Scientists at the Global Footprint Network have calculated that with this many people, using resources at the rate we do, we are extracting 1.6 times what the Earth can possibly regenerate. 

In other words, we’d need another 6 tenths of a planet to keep doing what we’re doing in any sustainable way. No es posible.

Humans have way overshot what the Earth can provide for us. This, ultimately, is why birds and countless other living things are in decline.

Now, having said all that… let me give you the answer regarding the top threats to birds. These are the proximate causes, or at least close to being the proximate causes. In order, from worst to slightly less worst, we have:

  1. Agricultural expansion
  2. Logging/Deforestation
  3. Invasive Species
  4. Hunting and Trapping
  5. Climate Change

So how did you do on our quiz? Were any of these things in your top three?

These threats vary from region to region. Logging might be the biggest threat in one country, while invasive species may take the lead in another.

And these threats don’t harm all bird populations equally. Some species and types of birds are more vulnerable to certain threats. 

Habitat Destruction

If you answered ‘habitat destruction’ to the quiz earlier, you’d be right.

Four of the five top threats are related to habitat destruction and degradation. Agriculture, logging, invasive species, and climate change can each destroy—or at least seriously trash—bird habitats.

Humans have been particularly destructive to forests, grasslands, wetlands, and other freshwater habitats.

At this point, a little over half of the planet’s land area has been completely converted to use by humans. In other words, less than half of the Earth’s natural habitats remain.

Even when habitats aren’t outright destroyed, human activities often chop them up into smaller and smaller fragments or patches. This fragmentation and isolation has enormously negative consequences for wildlife.

Okay, this is where I pause, take a deep breath, and fight my urge to break something because I’m so frustrated with humanity. That wouldn’t be productive, and it won’t help the birds.

Now let’s discuss each of the five big threats individually, starting with agriculture.


Too many people on the planet means enormous amounts of food needs to be produced. So… agriculture. 

38% of the Earth’s land surface is now devoted to growing crops and raising livestock.

Agricultural expansion threatens 74% of the world’s most threatened bird species. That’s 1,087 of the Red List species in the categories of critically endangered, endangered, or vulnerable. 

Land conversion from natural habitats to agriculture is happening fastest in the tropics. Unfortunately, that’s where most of the world’s terrestrial biodiversity lives, including most of our bird species.

Some of the most destructive crops in the tropics are coffee, sugar, palm oil, cocoa, and soy.

So basically all the good stuff. Except stupid palm oil. I wish palm oil were easier to avoid. It’s in, like, everything.

But, I sure had my coffee this morning and, as a vegetarian, I eat plenty of soy-based products. I’ll write another blog post where we focus on what humble folks like you and me can do to help protect wild birds and their habitats. We’ll talk about “bird-friendly” coffee and fun stuff like that.

Now, I said that livestock is included as part of the threat of agriculture. Not only is it part of the problem, it’s 77% of the problem. That’s the percentage of global farming land that is used for grazing and growing food for livestock. 

If we do a little calculating, we see that this means 29% of the planet’s land area, almost one-third, is being used to produce meat and dairy products.

In its State of the World’s Birds report, BirdLife International tells us that, globally, the average person eats about one-third more protein than they actually need, from a nutritional standpoint. That includes protein from animal and plant sources. 

So, as a species, humans are eating way more protein than they need. The United States and Europe are, of course, the worst offenders here. Ahem.

Only 37% of the protein that humans consume globally comes from animal sources. And yet one-third of the land on this planet is set aside for maintaining livestock. Crazy, huh?

Why am I pointing all this out? Because if you connect the dots, you get:

People eat too much protein, and the production of animal protein requires one-third of all the land there is. That land used to be natural habitat for birds. 

And we aren’t satisfied with the agricultural real estate we already have. Our conversion of wild habitats is ongoing. Agricultural expansion continues.

Agricultural expansion—both small and large scale—is a major threat to birds. Photo by Kimberly Vardeman.


Birds singing in a forest is perhaps the quintessential sound of the natural world. Humans have been listening to forest birds for millions of years—from the time when our primate ancestors were living in trees, sharing the branches with birds.

Two-thirds of the world’s birds depend on forest habitats. But since the year 1900, one-half of all forests on the planet have been destroyed. This has been devastating to birds.

Of the most threatened Red List species, 734 species—which is about half—are experiencing declines because of logging. 

People are chopping down trees for subsistence, at a small scale, as well as for commercial purposes at a large scale. 

This is for timber and paper, but also to clear land for crops, livestock, and biofuels. 

The latter activities amount to agricultural expansion, which is to blame for 80% of deforestation. So this is an example of how these major threats to birds can interact. 

Now, most birds can fly, right? So when their forest habitats are destroyed, can’t they just fly off to a new patch of habitat? 

Yes, and that’s what many do. But the overall loss of habitat area, the reduction in acres or hectares of forest, results in smaller bird populations. Small populations are vulnerable to decline and extinction. Small habitat patches can’t support as many individuals or species as large patches.

Another problem is that many forest birds are habitat specialists that require intact, relatively pristine forest. Some of these specialists don’t do much flying and/or they just aren’t capable of moving to a new patch of forest.

For example, the Bare-faced Curassow (Crax fasciolata) is a forest specialist in central South America. It’s a chicken-like member of the family Cracidae that forages for fruit on the forest floor. The male has a booming song that carries far through thick vegetation.

A forest specialist like the Bare-faced Curassow can’t or won’t move across large areas that have been cleared of forest. Populations of these birds get smaller and smaller as their habitat is fragmented. 

There is some hope that humans won’t cut down the remaining half of the world’s forests. The recently published Global Diversity Outlook from the UN reports that the rate of global deforestation between 2010 and 2020 was one-third less than it was in the previous decade.

Many countries and local jurisdictions now have laws in place to regulate logging. These can be helpful, for sure, but unfortunately, illegal logging is rampant in many places. This is a huge problem and by no means are we out of the woods.

Deforestation of pristine habitat in Malaysia. Photo by Richard Carey.

Invasive Species

Of all the known bird extinctions, over 70% were caused by invasive species. That’s 112 bird species we’ll never see again. So with respect to causing actual extinctions, invasive species take the gold medal. 

These are critters or plants that humans have shuffled around on the planet, either intentionally or accidentally. We dropped them off in places where they never existed before. Once introduced, these species spread and started causing mayhem.

Invasives are a major problem for 39% of our most threatened Red List bird species.

Rodents are the biggest threat, affecting at least 250 birds on our list. Rats and mice eat eggs and kill nestlings. When they’re introduced to a new island—almost always unintentionally by humans—they can quickly spread and start killing off naïve or helpless native birds.

The same thing happens with cats, which are the second most terrible invasive species with respect to native birds. Domestic cats are small killing machines that reproduce quickly. They can easily wipe out bird populations.

And then we have dogs, pigs, mongooses, goats, weasels, snakes, and so on. 

Some bird species are faced with threats from teams of these supervillains. A single tropical island might swarm with invasive rats, cats, goats, pigs, and mosquitoes, which can carry avian malaria. 

You know, I called these animals villains, but of course they aren’t to blame. It’s people who transport these species around, whether out of ignorance or indifference. 

Invasive species hurt birds by killing them outright, or they affect birds indirectly by damaging the habitats that birds require. Feral pigs, for example, gobble up native plants and small animals, and they tear up natural habitats like rototillers as they root around in the soil.

Invasive animals can sometimes just outcompete native species. European Starlings have been introduced to North America and elsewhere, and they compete with native birds for nest cavities.

Once they’re established, it can be super difficult if not impossible, to eradicate invasive species. Some of the best success stories are on tiny islands, such as some in New Zealand, where aggressive trapping and hunting programs can eventually get rid of the invasives.

The Brown Rat (Rattus norvegicus) is a destructive invasive species across the world. Photo by Dunpharlain.

Hunting and Trapping

Direct exploitation of birds by people has been and continues to be a major cause of their decline. Humans hunt birds for food and, sadly, for “fun,” or what some call sport. And birds are killed for their body parts. Particularly their feathers, but sometimes other structures like their bills.

The Helmeted Hornbill, for example, is now critically endangered due in part to habitat loss, but thousands are now being killed for their casques. These are the so-called “horns” on their beaks. Helmeted Hornbill casques are carved like ivory and sold as fancy trinkets in parts of southeast Asia. Since these birds are protected by law in every part of their range, all of these killings are illegal.

Illegal hunting and trapping are common problems worldwide. Sure, there are laws in many countries to protect birds or to regulate their exploitation, but enforcement of those laws is another thing.

Songbirds are hunted across the Mediterranean region where they’re eaten as a delicacy in Italy, Egypt, Malta, Cyprus, and elsewhere. For the most part, this hunting has been illegal for decades. And yet it continues.

The illegal capture of wild-caught birds for the pet trade is an enormous problem in some regions and for particular types of birds. For example, this is a major threat to many parrot species around the world.

Hunting and trapping are direct threats to at least 500 bird species on the Red List.

Illegally-captured Rufous-winged Buzzard (Bustatur liventer) in Thailand. Photo by Aerawan.

Climate Change

As if all this wasn’t bad enough, we also have good ol’ climate change. Human-caused climate change is hurting one-third of the world’s most threatened bird species. Trends in the climate data suggest that things will get worse. So, more and more species are likely to be affected in the future.

The rapid warming of the planet is causing more frequent and violent storms, serious droughts, massive wildfires, shifts in ocean currents, rising sea levels, and melting permafrost. Through these sorts of effects, climate change can exacerbate the other threats to birds we’ve been talking about.

Research has shown that many bird species are shifting their ranges as the planet warms up. Some species migrate farther from the equator in summer, while others move to higher elevations in the mountains. And the timing of migration has shifted for some species. 

Not all of these changes are necessarily bad for all birds. Some species’ populations are actually increasing because of global warming. But these species are in the minority. For most species, we don’t have enough data yet to understand how they are being affected.

When changing climate conditions don’t match up with deeply ingrained instincts in birds, things like mismatched migration timings can hurt populations. Birds don’t end up where they need to be at the right time of year. And some birds will lose habitat when the plants and/or insect prey they depend on disappear. Most of these changes are happening so fast that birds won’t have time to evolve, to adapt genetically to deal with them.

Hurricanes and cyclones are becoming more frequent and more severe as the planet heats up. Photo by NASA.

Other threats

There are other threats to birds we haven’t talked about. The list goes on. I’ll briefly touch on a few here.

Collisions with human structures are a big problem. Birds don’t always perceive or understand the danger of windows on buildings, or of power lines and wind turbines. It’s estimated that up to 230,000 birds die every year in New York City from crashing into buildings. The American Bird Conservancy reports that nearly 1 billion birds die from collisions every year in the US.

Even though DDT was banned in the US in 1972, and birds like Bald Eagles and Osprey have recovered, pesticides and other types of pollution are still major threats to birds in many regions.

Fishing gear can be a threat to seabirds like albatrosses. In some locations, many Wandering Albatrosses drown when they try to snatch squid and fish bait from commercial longline hooks.

The Okinawa Woodpecker

Let’s consider one particular species as a sort of poster child for some of the threats faced by the world’s birds.

The Okinawa Woodpecker (Dendrocops noguchii), which I mentioned earlier, lives on its namesake island in the far south of Japan. This bird is about 12 inches long or 32 centimeters. It’s dark brown with dull reddish highlights, and it has some nice white spots on its primary feathers. 

Only a few hundred The Okinawa Woodpeckers (Dendrocops noguchii) are left on the planet. Photo by Arjacee.

You aren’t likely to find an Okinawa Woodpecker outside of its habitat: pristine, subtropical, broadleaf forest in the mountains. These birds require large trees and lots of decaying wood to forage in. They need forests that are at least 30 years old. This habitat has already been greatly reduced by logging. And deforestation is ongoing. Trees are being cut down to make room for agriculture, dams, roads, and golf courses. Bloody golf courses.

Only 100-400 Okinawa Woodpeckers remain. With such a small population concentrated in one small area, this critically endangered species could be snuffed out by one fierce typhoon. Such storms are increasing in frequency and severity due to climate change. This bird also faces pressure from invasive mongooses and cats. It wouldn’t take much for this species to go extinct from any combination of these threats.

Reason for Hope

How does all this information make you feel? Probably not great.

When I get immersed in this stuff, I can experience a range of unpleasant emotions: Rage, disgust, sadness.

Such a reaction is warranted, I think. It should be clear that this conservation crisis is a really big deal. We need to get worked up about it. Because, of course, birds aren’t alone—the vast majority of life on this planet is threatened. By us.

I choose to take the energy of the anger and sadness I feel and redirect it to do something positive for birds and other wildlife.

Because this story is not all gloom and doom. I’m so encouraged to learn about the efforts of countless people across the world who are working hard to help birds. There is still so much good that we can do. And positive changes are happening all the time.

There are many wonderful success stories in conservation. For example, a recent study in the journal Conservation Letters estimated that since 1993 between 21 and 32 bird species would have gone extinct without conservation interventions. And 7-16 mammals were also saved.

Even though humans can be pretty stupid sometimes, so many of us really do love nature and we will do what we can to protect it. That’s a beautiful thing.

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