Auke-Florian Hiemstra, a biologist who studies how wild animals reuse human materials, thought he had seen it all. In his research on the common coot, a water bird often found in Dutch canals, he discovered nests containing windshield wipers, sunglasses, plastic carnations, condoms and envelopes used to package cocaine.

“So my definition of what is nesting material was already quite broad,” said Mr. Hiemstra, a doctoral student at the Naturalis Center for Biodiversity in the Netherlands. “Almost anything can become part of a bird’s nest.”

However, he wasn’t prepared for what he found when he went to investigate a strange nest that was spotted outside a hospital in Antwerp, Belgium, in July 2021. Nestled near the top of a sugar maple tree was a Eurasian pygmy nest that looked like. a cyberpunk porcupine, with thin metal bars sticking out in every direction.

“I couldn’t believe my eyes,” he recalled. “These are birds making a nest with anti-bird spikes.”

Rows of these sharp metal needles have become a common feature of the urban environment, installed on roofs and ledges to discourage birds from roosting or nesting on buildings. But outside the Antwerp hospital — where, as it happened, many of the roof spikes had disappeared — the magpies managed to convert hostile architecture into a home.

“They are outsmarting us,” said Mr. Hiemstra. “We try to get rid of birds, the birds collect our metal spikes and actually make more birds in these nests. I think it’s just a brilliant comeback.”

And the Antwerp magpies were not alone. Over the next two years, Mr. Hiemstra and his colleagues discovered several other nests, built by Eurasian magpies and carrion crows, that contained anti-bird spikes. They described their findings this week in an article published in Deinsea magazine.

“It’s absolutely fascinating,” said Mark Mainwaring, an expert on bird nests at Bangor University in Wales, who was not involved in the new study. “It shows how intuitive these birds are, and it shows a certain flexibility to go out and find these new materials and use them.”

Magpies and crows are both members of the corvid family, a group of birds renowned for their intelligence and problem-solving abilities. Magpies often build domed nests, joining thorny branches into roofs designed to protect against predators. In the nests that Mr. Hiemstra and his colleagues found, the magpies appeared to use the anti-bird spikes for the same purpose, turning them into a prickly nest cover.

“The Antwerp nest is really like a bunker for birds,” said Mr. Hiemstra, who calculated that it contains about 50 meters of anti-bird strips and 1,500 visible spikes. “It must feel really safe sitting in the middle knowing that there are 1,500 metal shards or pins protecting you.”

Although the researchers did not catch the magpies in the act of tearing the strips from the hospital roof, spikes disappeared from the area near the bird’s nest, and other birds were observed tearing such spikes from buildings. And sharp, human-made materials, including barbed wire and knitting needles, have previously been found in magpie domes, the scientists noted. (“That must be such a happy magpie coming home to the nest with this big knitting needle in its beak,” thought Mr. Hiemstra.)

The crows seemed to use the spikes in a different way, turning the sharp needles towards the inside of the nest. Although the idea remains unproven, positioning the spikes in this way could give the nests more structural support, Mr. Hiemstra speculated.

It’s not entirely clear whether the birds simply use the spikes because they’re available—in the urban wild, they might be easier to find than thorny branches—or whether they might be even better suited for the job than natural materials.

But the use of artificial nesting materials is common throughout the bird universe, according to new review of the scientific literature of Dr. Mainwaring and his colleagues, which was published in the journal Philosophical Transactions of the Royal Society B on Monday. They found reports of tens of thousands of nests – built by 176 different bird species, on every continent except Antarctica – that contained artificial materials, including plastic bags, cloth straps, fishing line, paper towels, dental floss, rubber bands and cigarette butts. .

“Where there’s an opportunity to incorporate anthropogenic materials, man-made materials, into your nest, you’re likely to do it as a bird,” said Jim Reynolds, an ornithologist at the University of Birmingham, in England, and an author. of the new review. “Some of it causes furrowed brows among us ornithologists, because you think, really?”

The findings reflect how much litter people leave behind, Dr Reynolds said, and research suggests the use of artificial nesting materials is becoming more common.

The long-term consequences are unknown. Bright or colorful materials could help a bird attract a mate – or catch the attention of predators. Research suggests that the chemicals in cigarette butts may help to protect nests from parasites – but it can also to be poisonous to birds And there are many reports of chicks becoming entangled in plastic string or rope that has entered a nest.

Regarding the use of the anti-bird spikes, Dr. Mainwaring was curious to see “if the behavior spreads, if other magpies see their neighbors using these spikes in nests and think: This is how you build a nest,” he said. “And the chicks raised in those nests will also grow up thinking it’s completely normal and natural.”

Mr. Hiemstra suspects that there are more pike nests waiting to be found out there. He sure hopes there is.

“I’m definitely rooting for the birds, cheering for the birds and actually enjoying the birds fighting back a little bit,” he said. “Because they deserve a place in the city just like us.”

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