Anti-bird spikes are used around the world to keep birds off buildings.
But clever magpies and crows in Europe have figured out how to use them to their advantage.
They have started using the spikes in their nests to keep other birds away.
Birds in Europe are getting their revenge on human-made anti-bird spikes by using them as weapons to protect their young.
Anti-bird spikes are usually placed on rooftops to keep birds from landing on buildings. These strips can be seen on virtually every skyscraper in the world.
But magpies and crows in Rotterdam, the Netherlands, and Antwerp, Belgium, have figured out that by using them in their nests, they could keep other birds and pests away.
The birds "appear to be using the pins exactly the same way we do: to keep other birds away from their nest," biologist Auke-Florian Hiemstra of the Naturalis Biodiversity Center who wrote a study about the phenomenon, said in a press release.
One of the nests, shown above, was found in Antwerp, Belgium. For this particular nest, magpies pulled up 150 feet of the spiky metal strip from the rooftop of a nearby hospital, creating "an impregnable fortress," said Hiemsa.
Hiemstra also regularly finds a whole host of other materials in the nests, including condoms, cocaine wraps, and fireworks, per the press release.
"It's like a joke, really," says Hiemstra said.
"Even for me as a nest researcher, these are the craziest bird nests I've ever seen," he said.
Hiemstra told the BBC that more research is needed to confirm the intent of the corvids using the spikes in the nest.
Though their placement suggests that these are meant as protection — the spikes are mostly placed outwards, he said — it's possible the birds just picked up whatever material was readily available to them.
Still, he sees this as a form of "beautiful revenge".
"They are using the material that we made to keep them away, to make a nest to make more birds," he told the BBC.
The behavior, which has also been spotted in the Netherlands and Scotland, isn't completely outside of the birds' normal wheelhouse.
Magpies, for instance, favor thorny branches to create a roof around their nests, keeping pests away from their young. Other spiky materials had previously been spotted in nests in the area, such as barbed wire and knitting needles.
Jim Reynolds, an ornithologist at the University of Birmingham, told The Guardian he wasn't surprised that the birds spotted using the deterrents to their advantage were part of the corvid family. This group of birds, which includes crows and magpies, is known for its creative problem-solving skills.
Crows, for instance, have been trained by a French amusement park to pick up cigarette butts and litter in exchange for a food reward.
"They are even more amazing than I think they are," said Reynolds, who was not involved in the study.
But it's not only corvids that have found a creative use for the murderous deterrents. Peregrine falcons in Amsterdam have previously been observed impaling their prey's remains on the spikes to save them for a later snack, the study reported.
The findings were published in the Natural History Museum Rotterdam's periodical journal Diensea on Tuesday.
Read the original article on Business Insider