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Birds have co-opted our anti-bird weapons in a genius counterattack

Humans install spikes so birds will go away. Birds steal them and do this instead.

Biologist Auke-Florian Hiemstra with a massive magpie nest made using anti-bird pins.
Alexander Schippers/Naturalis
Sigal Samuel is a senior reporter for Vox’s Future Perfect and co-host of the Future Perfect podcast. She writes primarily about the future of consciousness, tracking advances in artificial intelligence and neuroscience and their staggering ethical implications. Before joining Vox, Sigal was the religion editor at the Atlantic.

Humans are so cute. They think they can outsmart birds. They place nasty metal spikes on rooftops and ledges to prevent birds from nesting there.

It’s a classic human trick known in urban design as “evil architecture”: designing a place in a way that’s meant to deter others. Think of the city benches you see segmented by bars to stop homeless people sleeping there.

But birds are genius rebels. Not only are they undeterred by evil architecture, they actually use it to their advantage, according to a new Dutch study published in the journal Deinsea.

Crows and magpies, it turns out, are learning to rip strips of anti-bird spikes off of buildings and use them to build their nests. It’s an incredible addition to the growing body of evidence about the intelligence of birds, so wrongly maligned as stupid that “bird-brained” is still commonly used as an insult.

Just take a look at this crow nest from Rotterdam in the Netherlands, built with anti-bird spikes. The crows have cleverly pointed every spike inward so that, instead of harming the birds, the spikes will form a perfect lattice for a nest.

A crow’s nest made from anti-bird spikes.
A crow’s nest from Rotterdam in the Netherlands.
Kees Moeliker

Magpies also use anti-bird spikes for their nests. In 2021, a hospital patient in Antwerp, Belgium, looked out the window and noticed a huge magpie’s nest in a tree in the courtyard. Biologist Auke-Florian Hiemstra of Leiden-based Naturalis Biodiversity Center, one of the study’s authors, went to collect the nest and found that it was made out of 50 meters of anti-bird strips, containing no fewer than 1,500 metal spikes.

Hiemstra describes the magpie nest as “an impregnable fortress.”

A huge magpie nest made out of 1,500 metal spikes.
Auke-Florian Hiemstra

Magpies are known to build roofs over their nests to prevent other birds from stealing their eggs and young. Usually, they scrounge around in nature for thorny plants or spiky branches to form the roof. But city birds don’t need to search for the perfect branch — they can just use the anti-bird spikes that humans have so kindly put at their disposal.

“The magpies appear to be using the pins exactly the same way we do: to keep other birds away from their nest,” Hiemstra said.

Another urban magpie nest, this one from Scotland, really shows off the roof-building tactic:

A nest from Scotland shows how urban magpies are using anti-bird spikes to construct a roof meant to protect their young and eggs from predators.
A nest from Scotland shows how urban magpies are using anti-bird spikes to construct a roof meant to protect their young and eggs from predators.
Max Crawford

Birds had already been spotted using upward-pointing anti-bird spikes as foundations for nests. In 2016, the so-called Parkdale Pigeon became Twitter-famous for refusing to give up when humans removed her first nest and installed spikes on her chosen nesting site, the top of an LCD monitor on a subway platform in Melbourne. The avian architect rebelled and built an even better home there, using the spikes as a foundation to hold her nest more securely in place.

But Hiemstra’s study is the first to show that birds, adapting to city life, are learning to seek out and use our anti-bird spikes as their nesting material. Pretty badass, right?

The genius of birds — and other animals we underestimate

Studies like Hiemstra’s are important because they can challenge our conventional views of which animals possess intelligence and to what degree.

When we attribute a higher degree of intelligence to an animal, we’re more likely to include it in our moral circle, the imaginary boundary we draw around those we consider worthy of ethical consideration. (Mind you, some would argue that animal intelligence shouldn’t be measured by a human yardstick and that intelligence shouldn’t be the standard for inclusion in the moral circle anyway — maybe being sentient or even simply being alive is enough.)

It’s a well-established fact that many bird species are highly intelligent. Members of the corvid family, which includes crows and magpies, are especially renowned for their smarts. Crows can solve complex puzzles, while magpies can pass the “mirror test” — the classic test that scientists use to determine if a species is self-aware.

Studies show that some birds have evolved cognitive skills similar to our own: They have amazing memories, remembering for months the thousands of different hiding places where they’ve stashed seeds, and they use their own experiences to predict the behavior of other birds, suggesting they’ve got some theory of mind.

And, as author Jennifer Ackerman details in The Genius of Birds, birds are brilliant at using tools. Black palm cockatoos use twigs as drumsticks, tapping out a beat on a tree trunk to get a female’s attention. Jays use sticks as spears to attack other birds. New Caledonian crows turn spiny leaves into hooks for fishing grasshoppers, crickets, slugs, and spiders out of crevices. (As far as we know, that ability to make hook tools is shared with only one other animal on the planet: humans. Not even chimps or orangutans can do it.)

Birds have also been known to use human tools to their advantage. When carrion crows want to crack a walnut, for example, they position the nut on a busy road, wait for a passing car to crush the shell, then swoop down to collect the nut and eat it. This behavior has been recorded several times in Japanese crows.

But what’s unique about Hiemstra’s study is that it shows birds using human tools, specifically designed to thwart birds’ plans, in order to thwart our plans instead. We humans try to keep birds away with spikes, and the birds — ingenious rebels that they are — retort: Thanks, humans!

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