Birds are stealing anti-bird spikes put up by humans – and using them to build their nests.
Researchers from two Dutch natural history museums first came across the phenomenon in a hospital courtyard in Antwerp.
Magpies had ripped about 50m of anti-bird spikes from the hospital building and used them to build a huge nest of 1,500 spikes.
Anti-bird spikes are often installed on buildings to discourage birds from nesting there.
Biologist Auke-Florian Hiemstra of the Naturalis Biodiversity Centre said the magpies were using the pins in the same way humans do – “to keep other birds away from their nest”.
“It’s like a joke, really,” he said.
“Even for me as a nest researcher, these are the craziest bird nests I’ve ever seen.”
Magpies will make a roof on their nest to protect their eggs and young, and will often use thorny branches.
But in the city, anti-bird spikes offer an urban alternative.
The researchers described the behaviour as the “ultimate adaptation to life in the city”.
The research – published in Deinsea, the annual of the Natural History Museum in Rotterdam – describes similar magpie nests found in the Netherlands, Belgium and Scotland.
Crows have also been found making nests with the spikes in the Netherlands.
It’s not the first example of unhospitable items being used for birds’ nests.
Other sharp materials, including barbed wire and knitting needles, are also used by magpies for the roof of their nests.