Tennis players at the Stanley Park courts will briefly stop what they’re doing and look skyward, their attention drawn to a sudden crescendo of squawking from the treetops.
Like a scene out of a nature documentary, a bald eagle swoops down in an attempt — usually successful — to snatch one of the nesting baby herons with its talons or beak.
The attacks usually last just a few seconds — the herons rarely put up much of a fight — but the predator’s arrival sets off a chain-reaction of guttural cries that is hard to forget.
“The sound is the herons … screaming bloody murder,” said Scott Jutson, a frequent Stanley Park tennis player. “The noise the herons make in unison is pretty prehistoric. It’s a primal, survival scream.”
Jutson noted that an armada of crows will sometimes join the fracas and try to chase the eagles away, but the raptors don’t seem too bothered.
While regular players like Jutson have grown accustomed to the commotion, it can be quite startling for newer players to witness the violent ritual above their heads.
“That was wild!” one player blurted out on one recent evening.
A City of Vancouver press release in March heralded the return of the Pacific great blue heron colony for the 23rd consecutive year. At the time, 64 adult herons were counted.
“Last year, the colony brought approximately 90 new heron chicks into the world, overcoming persistent eagle raids and a late nesting season, due to more severe winter weather,” the release said.
The results of a recent survey by the Stanley Park Ecology Society showed 54 chicks and 15 eggs. The adult heron population is constantly in flux as many are out hunting due to the intense feeding needs of the chicks.
The city has even set up an online “heron cam” where people can get a close-up view of the herons’ daily rituals.
Heron colonies have existed throughout Stanley Park for at least a century, said Nadia Xenakis, urban wildlife programs coordinator with the society.
They moved to their current location in 2001. The area offers herons access to good foraging grounds, “but is in a terrible spot for increased human activity,” she said.
“At this point, the herons seem quite habituated to the activity, but it’s still important that we minimize disturbance to them when possible.”
To that end, there are several signs in the area reminding people to avoid loud noises and music, to not use drones or fireworks, and to keep dogs on a leash.
“Let’s respect park wildlife by giving them space,” one sign reads.
According to the city, the population of great blue herons has declined steadily since the 1980s due to habitat loss, nesting failures, human disturbances — and eagle attacks.
There are multiple breeding pairs of eagles in Stanley Park, “which may put this colony at a disadvantage for eagle raids,” Xenakis said.
Some researchers, however, have suggested herons will deliberately build their nests near bald eagles.
The theory?
Eagles are territorial and herons know this. So, the herons accept losing some — maybe 15 or 20 per cent — of their brood to the eagles, knowing those same eagles will keep other eagles away.
“We call it the mafia-protection racket,” Ross Vennesland, a researcher with Environment and Climate Change sa国际传媒, told former Vancouver Sun reporter Larry Pynn in a 2021 article in The Atlantic.
“Why they chose the location by the tennis courts is anybody’s guess really,” said Maria Morlin, a Vancouver Community College biology instructor who lives in the area and produced a documentary about the Stanley Park colony.
“My feeling is they chose the area because of the types of trees and numbers of deciduous trees — good for nests — in one area. … Some people think they chose it because it’s close to humans which may afford some protection from predators.”
When it comes to the eagle attacks, Morlin said they typically happen in the mornings and evenings. Early in the season, the eagles will target heron eggs, a high-protein food source that is easy to get “because the herons take off en masse to leave the eagles to it, basically.
“That’s because early in the season there hasn’t been too much energy expenditure by the herons, and they just lay more eggs. It’s a trade-off thing in animal behaviour, save yourself to have more offspring in future.”
Later in the season, the eagles will come for the chicks — even the nearly adult-sized juveniles. In these instances, the herons may put up more of a defence, “squawking and stabbing their beaks toward the eagle,” Morlin said.
But the eagles usually won’t leave without a meal.
“It’s a bit grisly, but eagle chicks need to eat, too.”
The area draws avid bird watchers, such as John Martin, 73.
“I like to come down here and listen to the fledglings,” he said one recent evening, noting that he always wears a hat because “the poop will dissolve the paint on your car.”
Joking aside, Martin noted herons’ reputation for being good barometers of the health of ecosystems. They are “top-end ecological beings,” he said. “If you have a strong colony, it means the ecology is coming back.”
He added: “As far as I’m concerned, eagles are just vultures.”
Professional photographer Manto Nakamura stood nearby, long-lens camera affixed atop a tripod. He had just witnessed an eagle attack earlier in the evening.
“I saw a bald eagle was attacking the baby and took it away to the sky,” he said. “Just 10 seconds — very fast.”
Nakamura didn’t capture the attack, but he did shoot the aftermath of the “shocked” parents overlooking their “empty nest.”
“Their life,” he said of the herons, “I think it’s very tough.”
