Picture a bird’s nest. Chances are, what comes to mind is a woven basket of twigs and plant fibers—you might not imagine a crown of metal spines. But that’s exactly how some crows and magpies in Europe have started styling their nests.
These clever corvids have commandeered anti-bird spikes—the long strips of needle-like rods used to repel birds from roosting on rooftops, doorframes or other human-made structures—and begun using them as nesting material, according to a new paper published this week in the National History Museum Rotterdam’s journal Deinsea.
“Even for me as a nest researcher, these are the craziest bird nests I’ve ever seen,” says Auke-Florian Hiemstra, a biologist at the Naturalis Biodiversity Center in the Netherlands, to the Guardian’s Ian Sample.
Let's start with crows. Crows seem to be able to build nests with anti-bird spikes! The spikes point inwards so they do not harm the bird. @HetNatuurhist in Rotterdam recently collected such a crow nest and you can see it in their museum! pic.twitter.com/fM4vrkvbOD— Auke-Florian (@AukeFlorian) July 11, 2023
Apparently, the birds remove the spikes from buildings, leaving behind tell-tale stripes of glue where the metal pieces once were, reports Emily Anthes for the New York Times.
“It’s absolutely fascinating,” Mark Mainwaring, an ornithologist and bird nest researcher at Bangor University in Wales who was not involved in the study, tells the publication. “It shows just how intuitive these birds are, and it shows a certain amount of flexibility to go out and find these new materials and use them.”
Crows and magpies are among the most intelligent birds. Both species have been documented to recognize their own reflection in a mirror as well as use tools. And in November, cognitive scientists reported that crows could understand a pattern-forming concept once thought to be unique to humans.
Now, that list of abilities can include repurposing metal spikes—an unusual strategy that might pay off for the birds, perhaps by giving them an evolutionary edge, Hiemstra tells the Washington Post’s Adela Suliman. “Animals always look at materials for their own gains,” he says to the publication.
The two species seem to be using the spikes in different ways—magpies add the pointed ends facing outward to protect their domed nests, and crows tend to turn the spikes inward, potentially for structural support.
In one example, the researchers calculated that a magpie nest outside a hospital in Antwerp, Belgium, included about 165 feet of metal strips and at least 1,500 individual spikes, writes the Times. This ultra-fortified lair is like a “bunker for birds,” Hiemstra tells the publication.
But on the flip side, the practice may harm birds in some circumstances, Mainwaring says to the Post. The metal spikes could become too chilly for chicks at night, for example. And using other forms of debris as nesting materials, especially eye-catching, colorful trash, could unintentionally attract predators.
Back to the anti-bird spikes. Ironically, these rows of upward-pointing spikes may be an appropriate substrate for a nest, as the pins help to secure the twigs, especially on sloping surfaces. Thanks, humans.pic.twitter.com/fLwnZKNsfi— Auke-Florian (@AukeFlorian) July 11, 2023
Whatever the trade-offs, birds all over the world are scavenging artificial materials to build nests. In a separate paper published this week in Philosophical Transactions of the Royal Society B, Mainwaring and a team of colleagues found evidence for nests incorporating human-made materials in 176 bird species on every continent except Antarctica. The material found in nests included plastic bags, fishing line, candy wrappers, paper towels, dental floss, straws and cigarette butts.
In the case of the spike-adorned nests, Hiemstra writes in a tweet that magpies “appear to be using the anti-bird spikes for their nest in exactly the same way we do: to keep other birds away.”
“I’m definitely rooting for the birds,” he says to the Times, “because they deserve a place in the city just like us.”
Editor’s Note, July 18, 2023: A reference to the Australian magpie, which is not related to the Eurasian magpie, has been removed.