The magpie nest with the anti-bird spikes that prompted the research (Credit: Alexander Schippers/ Naturalis/ CC-BY-SA-2.0)

Anti-bird spikes are commonplace in urban cities. The sharp pins and poles fitted on rooftops are meant to prevent birds from perching or nesting on buildings. But in an ironic turn of events, some intelligent birds are ripping out the metal rods and using them to build nests.

The birds' usage of the spikes came to light in July 2021. A hospital patient in Antwerp, Belgium, noticed an odd-looking magpie nest in the courtyard and alerted Auke-Florian Hiemstra. The biologist at the Naturalis Biodiversity Center in the Netherlands studies how wild animals repurpose human materials.

Magpies point the spikes upwards to protect their eggs (Credit: Auke-Florian Hiemstra/ X/ CC-BY-SA-2.0)

Over the years, Hiemstra has found nests containing various unusual items. They include windshield wipers, sunglasses, and even plastic flowers. But the sight of the magpie nest, with about 1,500 thin metal rods sticking out in all directions, was like none other he had seen.

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

In the following two years, Hiemstra and his team discovered similar nests in other parts of Belgium, the Netherlands, and Scotland. Magpies are known to build nests with domed roofs that contain thorny plants to protect their eggs. Hiemstra believes anti-bird spikes are an added security measure to keep predators away. The scientists never actually saw the birds pulling out the spikes. But the buildings near the nests always had a few missing.

Crows place their spikes inwards probably to fortify their nests (Credit: Auke-Florian Hiemstra/ X/ CC-BY-SA-2.0)

Heimstra's team also found Carrion crow nests with anti- bird spikes. However, while magpies position the metal rods outwards, the crows turn them inwards. The researchers, who published their findings in the journal Deinsea on July 11, 2023, believe crows may be using them to build stronger nests.

"They're outsmarting us," Hiemstra said. "We're trying to get rid of birds, [but] the birds are collecting our metal spikes and actually making more birds in these nests. I think it's just a brilliant comeback."

Magpies and crows belong to the corvid family, a species well-known for its intelligence. Past studies have shown that the birds can recognize and remember individual faces for many years. They can also solve complex puzzles and devise innovative tools to complete tasks.