Some flocks contains thousands of birds.

Some flocks contains thousands of birds.

Birds: When thousands move as one

Large flocks can be a marvellous site, similar to that seen in schooling fish.

Birds’ mastery of flight is no better exemplified than when they gather in flocks.

Shorebirds perform graceful aerobatics over the mud flats, geese travel from the Arctic in V-shaped skeins, and crows fly in orderly lines as they converge on a roosting site.

I wonder how many generations of people have marveled at these sights?

Small sandpipers, such as dunlin, form looping, cloud-like flocks as a defence against predatory falcons.

A flock can be composed of thousands of birds, moving as one, in almost perfect synchronicity. Studies since the 1970s, by J. Michael Davis, Wayne Potts and others, show that a rotation by one bird can set off a chain reaction that spreads through the entire flock, causing the group to turn from dark to light (or vice versa) in a flash.

The wave of motion quickly speeds up until the flock as a whole is reacting much faster than the birds could as individuals. Potts called this the “chorus line effect.”

Flocks typically clump into a tighter group when menaced by a predator, with each individual bird turning inwards towards the average position of the group.

Turning outwards, the bird would become isolated and vulnerable to attack.

The same type of motion is seen in schooling fish, such as herring, that bunch into a tight ball.

Birds take it a wing flap further, by twisting into ribbons of alternating light and dark, that give the whole flock a mysterious fluid look.

The flight of snow geese, in contrast, is comparatively stately. Skeins composed of two or three hundred birds travel hundreds of miles, the lead bird flying for a short time before sliding back into the group and another taking its place.

The V-shaped formation is highly energy-efficient, as demonstrated regularly by cyclists, slip-streaming in each other’s wake.

Crows are not everyone’s favourite, yet their intelligence and social behaviour are among the most advanced of all birds.

From late summer onwards, adults and young gather in communal roosts, typically choosing city buildings where they are safe from predators.

They form groups at staging areas en route, often with much calling and fuss, suddenly taking wing all together, as they join the ritual evening procession.

Thousands of birds converge on a few blocks, flying in from great distances in long straggling lines, as the light fades from the sky.

The suburbs are forsaken and the crows take over the town.

Anne Murray is the author of A Nature Guide to Boundary Bay and Tracing Our Past: A Heritage Guide to Boundary Bay, both available at bookstores or online at www.natureguidesbc.com

Surrey North Delta Leader

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

Surrey Fire Service at a garage fire in the 14400-block of 82A Ave on March 22, 2021. (Photo: Shane MacKichan)
‘Perfect storm’ of variants, increasing COVID cases are concerning for Surrey fire chief

Between police and fire, Larry Thomas said there are 8 confirmed cases, 18 others isolating

Surrey Fire Service is on scene of a fire in the 12300-block of 72A Avenue Saturday morning (April 10). (Photo: Shane MacKichan)
Surrey crews on scene of house fire

It happened in the 12300-block of 72A Avenue

Emergency crews on scene after a small plane crashed in a grassy area on the northeast side of Boundary Bay Airport Saturday morning (April 10). A freelancer said the plane caught fire and one person was transported to hospital by BC Emergency Health Services. (Photo: Shane MacKichan)
Small plane crashes at Delta’s Boundary Bay Airport

Plane appears to have suffered ‘significant’ damage, says freelancer

Signage on a South Surrey sidewalk reminds pedestrians to respect social-distancing guidelines. (Photo: Tracy Holmes)
Surrey records 4,400 COVID-19 cases in March

New cases almost doubled between February, March

Surrey RCMP are looking for these two men after a bank in the 12800-block of 96th Avenue was robbed on March 12. (Images: Surrey RCMP)
Police release images of two men suspected of robbing Surrey bank

Robbery happened on March 12 at bank in 12800-block of 96th Avenue

B.C. Health Minister Adrian Dix and Premier John Horgan describe vaccine rollout at the legislature, March 29, 2021. (B.C. government)
1,262 more COVID-19 infections in B.C. Friday, 9,574 active cases

Province’s mass vaccination reaches one million people

A vehicle that was driven through the wall of a parkade at Uptown Shopping Centre and into the nearby Walmart on April 9 was removed through another hole in the wall later that night. (Photo via Saanich Police Department and Ayush Kakkar)
Vehicle launched into B.C. Walmart removed following rescue of trapped workers

Crews cut new hole in parkade wall to remove vehicle safely

Four members with Divers for Cleaner Lakes and Oceans were out at Cultus Lake on March 28 and 29 hauling trash out of the waters. (Henry Wang)
PHOTOS: Out-of-town divers remove 100s of pounds of trash from Cultus Lake

Members of Divers for Cleaner Lakes and Oceans hauled out 470 pounds of trash over two days

As of Saturday, April 10, people born in 1961 are the latest to be eligible for a COVID-19 vaccine. (Black Press files)
B.C. residents age 60+ can now register to get their COVID-19 vaccine

Vaccine registration is now open to people born in 1961 or earlier

A new saline gargle test, made in B.C., will soon be replacing COVID-19 nasal swab tests for kids. (PHSA screenshot)
Take-home COVID-19 tests available for some B.C. students who fall ill at school

BC Children’s Hospital plans to provide 1,200 kits to Vancouver district schools this April

Ruming Jiang and his dog Chiu Chiu are doing fine following a brush with hypothermia that saw several people work together to get them out of the Fraser River near Langley’s Derby Reach Park on March 25, 2021 (Special to the Advance Times)
Man finds men who rescued him from drowning in B.C.’s Fraser River

A grateful Ruming Jiang says he will thank them again, this time in person when the pandemic ends

The 10-part Netflix series Maid, which is being exclusively shot in Greater Victoria, was filming near Prospect Lake in Saanich last month. (Photo courtesy Fred Haynes)
Province announces $150,000 towards film studio, fulfilling B.C. NDP promise

Investment to fund movie studio feasibility study at Camosun College

Tyson Ginter, 7, is proud of his latest Hot Wheels he recently received by Quesnel RCMP Const. Matt Joyce. (Photo submitted)
B.C. Mountie handing out toy cars to light up children’s faces

‘A lot of times it will be the only interaction they have with the police,’ says Const. Matt Joyce

People stroll through rows of tulips in bloom during the Tulips of the Valley Festival on May 2, 2017. The colourful spring event, now called Chilliwack Tulips, opens on Sunday, April 11, 2021. (Jenna Hauck/ Chilliwack Progress file)
Fraser Valley tulip attraction returns this weekend for 1 month

More than 6.5 million bulbs in all at this year’s colourful Chilliwack Tulips event

Most Read