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Deforestation is killing tropical birds, but not in the way that you might think.
They’re starving to death because they can’t get an Uber Eats driver.
The birds are relying on an important service provided by ants.
And that service requires large, intact forested areas.
In other words, it’s a tale of dominoes falling one after the other.
When we think about deforestation,
we normally think that loss of habitat is what causes animal populations to decline.
After all, animals lose their homes and sources of food.
But the way a forest is cleared matters, as well.
Forest fragmentation occurs when a large forested area is broken into small, isolated patches.
It can mean that species don’t have enough space to search for sufficient food,
or can’t easily travel into other forested areas.
For the various species of birds collectively called antbirds,
fragmentation like this is especially deadly.
And not because their trees or food source is gone, really, but because their dining buddies are.
See, antbirds have that name not because they eat ants,
but because they follow after ants to get food.
In this case army ants, specifically.
Army ants are found in tropical rainforests in Africa
and South and Central America, such as the Amazon.
They hunt by going on raids that can be many hundreds of thousands of ants strong,
and their colonies are much larger than those of other kinds of ants.
I’m talking a million workers alone making up a raiding party.
Instead of foraging individually for crumbs of food to bring home like a typical ant,
army ants hunt together to catch live prey,
including other animals way bigger than themselves.
Of course, that’s usually still other insects, including their favorite: other ants.
Larger individual insects, though, like grasshoppers and cockroaches,
will scatter from approaching army ant raids,
and then get snapped up by the hungry antbirds who are lying in wait.
It’s a pretty smart tactic, and makes for easy meals for the antbirds.
A set up like this means antbirds don’t need to work much to get their food,
especially when their home range is full of a reliable
army ant species that raids nearly every morning.
Some species of really committed ant-following birds
get upwards of 50 to 70% of their total diet from following these raids.
And it’s those committed species that are most at risk.
Because they’ve foraged and fed with ant support for so long,
these antbirds can no longer hunt by themselves effectively,
and can’t feed themselves well any other way.
After generations of adaptation, these specialist species may just
not have the right behavioral skills for hunting independently any more.
And while researchers continue to untangle antbird ant-preferences and behavior,
we also keep cutting down rainforests and fragmenting their homes.
Naturally, fragmentation harms the army ants first.
For as small as they are, they need large,
continuous space for their raids, and quantity is more important than quality of space.
And I do mean large.
For a single army colony of 10,000 to 10,000,000 ants to
meet its energy demands and survive, it requires up to 30 hectares of land.
That’s 300,000 square meters, or almost 100 football fields.
A colony doesn’t stay put, either.
It goes through periods of low activity, active raiding, and home relocation.
Raids usually spread out from home in a fan shape,
and a new home is usually selected along the same compass direction.
This helps a colony avoid re-raiding food sources that they’ve already cleared out.
You know, keeps things fresh.
It also means a single antbird needs to seek out
multiple army ant colonies in their range to stay well fed.
So when we cut down trees and make smaller pockets of forest where there used to be
larger continuous forested area, army ant colonies start to die out first.
Without enough ant colonies conducting regular raids, the poor antbirds go hungry.
Not because their preferred food has died out,
but because their Uber Eats driver is gone and they don’t know how to find their own food.
Now, not all army ant species are quite this sensitive to fragmented forests,
which means a savvy antbird could just go find another swarm for their dinner date.
Unfortunately, other army ant species often have different plans.
Some species just have the wrong schedule.
Antbirds like to follow ants that raid through most of the day and afternoon, but not at night.
And some species don’t raid so frequently, or not at all during the dry season,
leaving whole chunks of the year for the antbirds to be on their own.
So that’s a no-go.
And some army ant species hunt their prey underground,
which isn’t going to work for a bird either.
The best solution is simply preserving intact forest to help protect the ants and the birds.
But because of the role of fragmentation, it isn’t enough to simply maintain a certain
total amount of green space left behind by deforestation.
We also need to consider maintaining contiguous green space
to ensure army ants have enough room to raid and thrive .
To be fair, army ants are not the most charismatic species.
So if you aren’t moved to protect the forests for them, then do it for the birds.
Or maybe for the butterflies that eat fresh antbird poop in order to get nutrients important for laying their eggs.
Or the tropical lizards and frogs that also eat the escaping insects.
Or the raptors that follow the raids in order to eat the antbirds.
Or really any number of other animals in this big, connected, forest food web.
And we of course are all connected by this here World Wide Web
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