They hatched six weeks ago, watched by thousands of Melburnians who were stuck inside under the coronavirus lockdown. Now, as life is beginning to return to the city below them, three peregrine falcon chicks roosting on a city centre skyscraper are also preparing to leave the nest.
By Friday they will be ready to take flight, says Victor Hurley, the founder of the Victorian Peregrine Project, which monitors the birds in conjunction with BirdLife Australia. Then they will be made to move on – peregrines are fiercely territorial, and won’t tolerate their chicks remaining near home.
“Once they fledge, the adults will drive them out of the territory,” Hurley says. “Once each one makes its first kill the adults will stop getting food for them and they are out.”
Male hatchlings, which mature at 500g, would have flown the coop last week, but female peregrines weigh about 300g more and are slower to develop, Hurley says.
Females usually fly at least 50km from their nest to find a new territory, while males only go about 25km.
Neither the fledglings nor their parents wear tracking bands, so their many online fans will not be able to follow the birds once they leave the nest.
The saga began in late August, when a pair of falcons – believed by Hurley to be the same pair which have nested atop 367 Collins Street since the building owner Mirvac installed cameras four years ago – arrived at the newly renovated nesting box.
The box sits on the ledge of a window high on the south-east corner of the building. The site has been used for decades by pairs of falcons but only one pair at a time, and all have shown a preference for this corner, which Hurley says allows them to gather the morning sun but ensures their chicks don’t cook on hot spring afternoons.
This is the most successful breeding season for the Collins Street falcons in three years, Hurley says. In drier conditions, their prey – street pigeons, starlings and sparrows – are riddled with parasites, which can kill the fledglings.
With a wetter spring providing an abundance of food in green spaces including Albert Park Lake and the botanical gardens, the small birds in the city are in better condition. Those urban green spaces are essential to maintaining the health of the falcons, says Hurley.
“All the prey is in really good condition so it doesn’t have the parasite load,” he says. “In previous years those fledglings that were going to succumb were dead by this stage.”
Just 10% of fledglings go on to have a successful breeding season of their own. They can live for up to 16 years but most don’t make it beyond six.
“I suppose it’s an artefact of an adrenaline-based lifestyle – they are the fastest animal on the planet and they tend to live hard and fast,” Hurley says.
The male adult falcon nesting at Collins Street specialises in sparrows and starlings, while the female brings in bigger pigeons. Hurley says he has seen a female peregrine falcon take down an ibis before, although she gave herself a concussion in the effort and, because it was three times her bodyweight, she was unable to take it back to her nest. There is also a report of a female peregrine falcon killing a wedge-tailed eagle in a territorial dispute.
The falcons are ruthless in defending their patch, Hurley says, and nesting sites are prized. Peregines prefer sheltered ledges on the sides of cliffs – or skyscrapers – but in Victoria they have also been known to roost in hollows of towering river red gum trees and in nests stolen from birds with better construction skills.
“These things are like really bad tenants,” Hurley says. “They know what a house is but they don’t know how to maintain it, so they nest somewhere until it falls apart, then they find a new nest.”
The closest he has seen two peregrine falcon pairs nest, in 25 years of studying them, is 1.6km apart. The closest nesting sites to the Collins Street tower are in Altona and Sunbury, and Collins Street is often subject to territorial disputes.
“The resident female was knocked out of the sky and picked up on Collins Street,” Hurley says. “She was taken to a wildlife carer and able to be released in two days, then she proceeded to beat up the interloper, who was never seen again.
“She probably killed it. They are not much for taking prisoners.”