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Eurasian magpies typically build their nests from thorny branches, but some birds have discovered anti-bird spikes work just as well—if not better. Photograph By Auke Florian Hiemstra

'The Perfect Revenge'? Birds are Building Fortresses From Anti-bird Spikes

Despite a plethora of products designed to keep birds off buildings, our feathered friends are sending a clear message: Nice try.

— By Jason Bittel | July 17, 2023

In an example of “The Perfect Revenge,” European birds are ripping anti-bird barbs off buildings and using them to build armored nurseries for their chicks, scientists say.

“They take the stuff we use to try to deter birds, and they make a nest out of it, and then make more birds,” says Auke-Florian Hiemstra, a biologist at Naturalis Biodiversity Center in the Netherlands and lead author of a study on the phenomenon published this month in Deinsea, the online journal of the National History Museum Rotterdam.

“That’s just a brilliant way to fight the system. Nice to see some birds fighting back.”

While birds are a common urban neighbor, city residents don’t always appreciate the droppings and nesting materials our feathered friends leave behind. This has spurred an entire industry of products designed to keep birds off human infrastructure, such as light displays, netting, and even sharp metal spikes.

However, a new study shows that not only are some birds unbothered by long strips of barbs, but they’re actually ripping the skewers off buildings and using them to build armored nurseries for their chicks.

In the Netherlands, two instances so far show that carrion crows coiled the strips so that the spikes faced inward, possibly serving as a base for the nest and helping to bind other nesting materials, such as twigs and dry leaves.

Scientists want to know if these nests (Pictured, One Found in Antwerp, Belgium) ​are better at protecting chicks than those without spikes. Photograph By Auke Florian Hiemstra

Eurasian magpies, on the other hand, build nests with a roof. “Magpies are very worried about crows stealing their eggs and young, so to protect them, they make this dome,” says Hiemstra. “They can fly multiple kilometers trying to look for material. However, in cities, there’s not a lot thorny branches around.”

Perhaps this is why, in three separate instances described between 2021 and 2023 from the Netherlands, Belgium, and Scotland, Hiemstra found magpie nests that incorporated anti-bird spikes in the top of the dome. And this is intriguing, because magpies typically construct their roofs out of hawthorn, blackthorn, and rose stems.

In other words, it seems the magpies are not treating the anti-bird strips as just another building material. They’re using the spikes as spikes.

If true, it would be the first such documentation of its kind.

'Magpies are Nuts'

To be clear, birds build nests from human-made objects all the time. Hiemstra has personally seen nests from various species made out of everything from windshield wipers and headphones to hypodermic needles, cocaine packaging, and condoms.

“So even the wild side of Amsterdam, you will see reflected in the bird nests,” he says. “Almost anything can become nesting material.”

However, for his new research, Hiemstra dived into the scientific literature to find examples of corvids using anti-bird spikes. The first recorded example of this behavior appears to be from 2009 in Rotterdam, but overall the scientists gathered five instances in three countries.

“So even the wild side of Amsterdam, you will see reflected in the bird nests,” he says. “Almost anything can become nesting material.”

It has also been previously documented that some species, such as cockatoos in Australia, will actively rip anti-bird spikes from their moorings.

This strip of anti-bird spikes was taken from a nest in Antwerp, Belgium. Photograph By Auke Florian Hiemstra

However, what makes this new study different is the idea that the magpies, especially, may be using the anti-bird spikes in a functional capacity.

“I’ve seen birds who built on top of the spikes,” which are also used in the U.S., says Karina Sanchez, an urban ecologist at the University of New Hampshire not involved in the study. “But this was my first time seeing the spikes being yanked off of the structure and used in nests.”

Sanchez says she’s not surprised about the species involved. “Magpies are Nuts,” she laughs. “Their nests are very elaborate. We used to call them ‘condos.’”

While the photos included in the study are “somewhat convincing,” Sanchez says that right now, the idea that magpies might be using the spikes functionally is “still kind of anecdotal.”

For one, the behavior has only been documented a handful of times. And two, it would require further experimentation to prove that the magpies recognize the human-made materials as being similar in function to natural materials, such as thorny branches.

At the same time, Sanchez says, “I don’t see why that wouldn’t be a possibility.”

According to Hiemstra, the next step will be to design experiments that can figure out if thorny materials help magpies raise more chicks. Then, they’d want to see if anti-bird spikes produce similar, or maybe even better results.

Do Animals Feel Revenge?

The study comes among two recent examples of wildlife messing with people—an otter stealing surfboards in California and a spate of incidents in which orcas are attacking boats in Europe. These incidents have spurred headlines that wildlife is finally fed up with people.

Of course, scientists can’t say—yet—whether an animal actually feels revenge, Hiemstra says.

“If the birds themselves understand the irony of the whole situation, that is of course, impossible to say. But corvids do understand a lot, are real problem solvers, recognize themselves in mirrors, [and] understand tool use,” he says.

And it’s indisputable that wildlife have figured out how to live among us, especially in cities.

“It’s really sad that we’re fighting our urban wildlife so actively,” says Hiemstra, “while actually, it’s quite beautiful that these animals are living in cities, just like us.”

“So I would really like the people to embrace that urban wildlife, instead of fighting it with bird spikes.”