The 76-year-old man was riding his bike in Nicholson Park in Wollongong, south of Sydney, when he veered off the path to avoid a swooping magpie, according to Wollongong Police.
He then crashed into a fence post, was thrown to the ground, and suffered serious head injuries. The man was airlifted to Sydney's St. George Hospital and died that evening, police said.
Magpie swooping season occurs each year across the country in September and October, during Australia's springtime. This year, the season started early after a warm winter, according to CNN affiliate Seven News.
The territorial birds begin breeding in August and often swoop to protect their young from perceived threats.
Visitors to Australia might notice people walking around carrying large sticks, or bike riders wearing helmets with a dozen zip ties positioned so they stick up into the air.
Just over a foot in length, magpies can cause quite a bit of damage with their sharp beaks and sudden attacks -- last year, a toddler in Perth narrowly avoided being blinded by a magpie after it swooped down and attacked his face as he sat in a pram.
So far this year, there have been 1,570 swoopings nationwide, resulting in 189 injuries, according to the community-run Magpie Alert website. The number will likely go up -- last season, there were more than 3,000 reported swoopings.
The highest number of reported attacks so far this year are along Australia's east coast, in Queensland, New South Wales, and Victoria.
Magpies are a protected native species in Australia and it's illegal to kill them or take their eggs or chicks. Local councils will act if one is reported to be a real menace, otherwise residents are urged to stay away from trees where they are known to breed.
Magpie Alert warns that injuries tend to occur when cyclists fall off their bikes during an attack, like the man in Wollongong. Of all the attacks reported on the site, almost 70% occurred while people were cycling, 22% happened when people walked by.
To stay safe during swooping season, cyclists are advised get off their bike during an attack, and to keep calm instead of flailing -- which may come across as aggressive behavior and provoke the birds further.