During springtime in Australia, people taking a stroll or on a bike often face the risk of a bird strike by a native magpie.
Typically, it begins with the sensation of a fast-moving shadow closing in before the clawed, sharp-beaked, black-and-white bird lunges from above.
In most cases, these swoops are defensive attempts to keep passers-by away from nests during the breeding season from August to November, but they can result in serious injuries.
This year has seen a surge in such attacks, prompting concerns that the changing climate or increasing urban development may be affecting the birds' behaviour.
Across Australia, there have been 3,375 attacks and 540 injuries linked to magpies this year, according to Magpie Watch, a social media website which monitors attacks.
The Royal Victorian Eye and Ear Hospital in Melbourne treated 56 bird-strike injuries from July to last month, compared with 20 for the same period last year, according to figures released on Oct 20.
In the first 20 days of this month, there were 19 injuries, compared with eight for the whole of October last year.
3,375 Number of attacks linked to magpies across Australia this year, according to Magpie Watch, a social media website that monitors attacks. It also reported 540 magpie-related injuries.
The hospital warned that magpies' beaks and claws could cause serious injuries such as corneal lacerations and abrasions and that dirt left in the eyes could cause infections.
The state of Victoria has created a map which records the locations of all swooping-bird incidents.
While magpies are the main culprits, other Australian birds that can swoop include laughing kookaburras, red wattlebirds and magpie-larks, which are smaller and whiter than standard magpies.
Some bird experts say magpies have been unfairly maligned.
"Magpies are not naturally aggressive and this nest-protective behaviour usually occurs only for four weeks per year," Professor Gisela Kaplan, an expert on animal behaviour, told The Sunday Times.
Magpies are able to recognise individual human faces, she said. "If they know the individuals and have decided that they mean no harm, they will never swoop."
Magpies in Australia tend to be found in parks, sports fields and green areas alongside open spaces.
Prof Kaplan, from the University of New England, believes the reported rise in attacks this year may be due to encroaching urban development and shrinking green spaces, which threaten the birds' habitat and cause closer interaction with unfamiliar humans.
Additional stress factors, she said, could be increased noise or light levels at night or unseasonal or severe heatwaves, drought or downpours due to the changing climate.
The Victorian government has published a series of tips to people in well-known swooping hot spots.
These include travelling in a group; moving quickly through the area but not running; wearing a hat or carrying a stick or umbrella above one's head; and even drawing a pair of eyes on the back of headgear so that the birds think they are being watched. Cyclists are advised to wear a helmet, dismount and walk.
The threat has prompted novel inventions, including an "anti-magpie cycling helmet" with a garden hose connected to party poppers that the cyclist can blow into and make noise to ward off the birds.