"Many birds such as butcherbirds, magpies and miners nest in this area and may swoop on passers-by," the signs warn. "This is a normal protective behavior during the breeding season and lasts up to six weeks."
The signs advise: Avoid the area during breeding season; wear a hat or carry an umbrella, bike riders dismount and walk; and move quickly through the area — don't run.
City council workers managed to capture the magpie, before cordoning off the area and erecting several more of the warning signs at the site.
Sean Dooley from BirdLife Australia told ABC the organization was "shattered" over the incident.
"While it's only the male magpies that swoop and only 10 per cent of males do swoop … the consequences, especially when people are caught unaware, can be truly terrifying and devastating," he said.
He said Australia's magpie swooping season occurs between July and December, but peaks in September.
"Swooping season only occurs when the male magpies are defending the chicks in the nest – so for that brief period where the chicks are really vulnerable."