WATCH: Bird caught throwing stones at cars in Belconnen has biologists baffled

“Bad bird behaviour” is leading to damaged car and house windows in a Belconnen neighbourhood, and the experts aren’t clear why.

It started in November last year when Betty Macharia first noticed the black birds tapping on her home’s windows, but by January, they had turned on her car.

The resident finally caught one of the culprits on camera earlier this week picking up a stone in its beak and hurling it into the windows of her Volkswagen Golf. The force was strong enough to leave it pockmarked with chips, and she was one of the lucky ones.

“So far, a couple of cars have damaged windscreens needing replacement from the behaviour,” she told Region.

“The birds also knock on home windows and basically throw stones, damaging paintwork. They move in a pack and unfortunately won’t stop even after being shooed away – they just move to the next car.”

Betty pleaded with the Canberra Notice Board Group on 13 February, asking for “information to understand this behaviour and what can be done – if anything – to stop them from continuing”.

It turns out it’s not unheard of.

About eight years ago, Ian Douglas had to take his car to a windscreen repairer after he parked outside a high-rise apartment complex on Northbourne Avenue and came back to find a crack down the rear window.

“The repairer informed me birds had been dropping stones onto vehicles, as he had quite a few to replace in that area,” he told Region.

Ian ended up buying a reflective window shade but placing it outside the car and pinning it in place with the doors.

Andrew Govender from Canberra Windscreens says damage from birds is “very common actually”, even if he’s not sure what he sees in the workshop is the result of stones or beaks.

“I might get a couple a month. I think they see their reflection and just start pecking at the windows. Windscreens not so much, but side windows and the mirrors definitely.”

Matt Sandford, the owner of Aussie Windscreens, told Region he sees damage from birds accidentally dropping fruit pits onto windows.

“It’s hard to speak on behalf of a bird if they’re doing it on purpose,” he said.

“I’ve had people say it’s deliberately targeted, but I’ve also had people say the passing truck deliberately threw a rock at me.”

Ian Fraser is a Canberra naturalist and confirms the species in Betty’s video as the white-winged chough, common to the city. As for what they’re doing, it’s “really interesting”.

“I don’t find it all implausible a bird could learn to break a window to get at food on the other side,” he says.

“But I can’t make sense of it.”

Lucy Aplin from the Australian National University (ANU) Research School of Biology says many animals use hard surfaces as “anvils” to break open nuts or snails and get at the goodness inside, and “it’s just unfortunate … the local chough group decided glass is a good anvil”.

“Maybe it initially picked up a nut fallen on the car bonnet and broke it open by hitting it against the nearest flat, hard surface – the windshield – and that worked well, so when it picked up a nut on the ground, it took it back to the same place to crack it open.”

Another theory, suggested by Melbourne-based ecologist Dr Grainne Cleary (and author of the book Why Do Birds Do That?) is more sinister.

“I think the bird is doing it to break the windscreen,” she told ABC radio.

“It’s picking up a stone and using it as a tool to break the window. I read the Facebook page, and some people are wondering if the bird is attacking its reflection with the stone. I don’t think so because when another individual confronts the bird, it doesn’t pick up a stone to attack the other individual … It could be doing it because it’s experimenting.”

Who knows? Maybe another chough is waiting around the corner to talk to Betty about her car’s extended warranty.