A heron colony that nests in Stanley Park regularly produces more than 100 fledglings, but this year there were only 61.
Published Thursday, August 24, 2017 7:09PM PDT
The number of heron chicks surviving in Vancouver’s Stanley Park is dropping dramatically, and biologists are blaming another avian resident of the area.
Pacific great blue herons have nested in the park’s trees for nearly a century, but this mating season the colony’s fledgling population dropped.
The Stanley Park colony typically produces more than 100 fledglings each year. This season, only 61 chicks survived.
A Pacific great blue heron eyes a CTV News camera in Vancouver’s Stanley Park on Thursday, Aug. 24, 2017.
A bald eagle is seen on a Stanley Park nest cam preying on fledglings or stealing eggs.
“We measure nest success: How many nests were there? How many successfully raised a chick that was able to fly away?” Greg Hart explained.
The urban wildlife program coordinator for the Stanley Park Ecology Society said the success rate was around 52 per cent this year, down from an average in the mid-80s.
Heron nest cams, which livestream the trees the birds are known to frequent, showed the reason for such a dip in nest success.
“We witnessed quite a few eagle attacks, and because of this, we know for a fact that a handful of nests did fail,” Hart said.
Maria Morlin, a biology instructor at the Vancouver Community College, said eagles have been known to swoop in and steal eggs and chicks. This year it seemed to happen more frequently, she said.
“People don’t realize birds eat birds in the same way mammals eat mammals,” she said, likening the eagles eating herons to lions feeding on antelope.
Morlin, who is working on a documentary about the Stanley Park colony, said she’d gathered a considerable amount of footage of bald eagles preying on nests.
And the eagles are not the only threat the youngest members of the colony have faced.
A few years ago raccoons were seen scaling the trees to get at the eggs, so the Vancouver Park Board installed pieces of metal on the trunks to deter the furry bandits.
“Raccoon predation events have dropped to practically zero,” Hart said, but there’s little the board can do to protect the herons against predators that approach from above.
Hart said even if there was something they could do to keep the eagles at bay, ecologists aren’t sure they would intervene.
“You can’t really choose sides in it. Both are really trying to raise their young, and that’s nature sometimes,” he said.
With a report from CTV Vancouver’s Shannon Paterson