An elderly man has died of head injuries after he was startled by a magpie and crashed his bicycle south of Sydney.

The 76-year-old was riding a pushbike on an off-road path alongside Nicholson Park at Woonona, Wollongong, on Sunday morning when witnesses report he veered off to avoid a swooping magpie.

He collided with a fence post and was thrown to the ground, and suffered serious head injuries.

The man was airlifted to St George Hospital in a critical condition but died later that evening.

AAP

Magpies usually breed between August and October, which means they are more likely to swoop people in an attempt to protect their eggs or chicks.

According to Magpie Alert, a website that collects reports of magpie swooping incidents, cyclists are the most common target of swooping, encompassing 69 per cent of reports so far in 2019.

Earlier this month, a Sydney council shot dead a "particularly aggressive magpie" after it had allegedly injured a number of people.

More than 40 complaints had reportedly been lodged with the Hills Shire Council about the magpie, which attacked people on Bella Vista's Old Windsor Road, ABC News reported.

"[It was] swooping underneath helmets ... to attack people's faces," a council spokesperson said in a statement.

"This bird was very aggressive and uncharacteristically territorial."