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

Court of Appeal in Vancouver. (File photo: Tom Zytaruk)
Man convicted of assault, unlawfully confining woman pregnant with his child loses court appeal

Victim tells court he drove her to Guildford parking lot after he’d ‘grabbed’ her neck and she fainted

Peter and Stephanie Chung. (File photo: Tom Zytaruk)
Surrey philanthropists presenting $285K in scholarships on Saturday

Drs. Peter and Stephanie Chung over the past nine years have awarded more than 500 students, in memory of their son Joseph

North Surrey Minor Football players in action. The club is among Surrey-area recipients of the B.C. government’s Local Sport Relief Fund. (File photo)
COVID ‘relief’ funding for some sports groups in Surrey, White Rock, Delta

‘Without financial support, these clubs are at risk of closure,’ says B.C. government

Businesses continue to struggle under COVID-19 restrictions as the pandemic reaches the one-year mark. (B.C. government)
Another 564 COVID-19 cases, mass vaccine plan coming Friday

15 more deaths, community cluster declared in Williams Lake

A specialized RCMP team is investigating a suspicious trailer, which might have connections to the illicit drug trade, found abandoned outside a Cache Creek motel. (Photo credit: <em>Journal</em> files)
Police probe U-Haul trailer linked to illicit drugs left outside Cache Creek motel

Hazardous materials found inside believed to be consistent with the production of illicit drugs

Premier John Horgan leaves the podium following his first press conference of the year as he comments on various questions from the media in the Press Gallery at B.C. Legislature in Victoria, B.C., on Monday, January 13, 2020. THE CANADIAN PRESS/Chad Hipolito
Interprovincial travel restrictions a no-go, Horgan says after reviewing legal options

The B.C. NDP government sought legal advice as concerns of travel continue

Gem Lake Top, at Big White Ski Resort, seen at Jan. 8. (Big White Ski Resort)
Big White cancels $7.3M in lift tickets, accommodations due to COVID-19 orders

Since November, the ski resort has been forced to make several changes

Darlene Curylo scratched a $3M ticket, BCLC’s largest ever scratch and win prize. (BCLC)
Kelowna woman in shock after winning BCLC’s largest-ever instant-ticket prize

Darlene Curylo couldn’t believe her eyes when she saw the amount of money she’d won from a scratch ticket

While each person has different reasons for becoming homeless, a UBCO study shows they learn through their interactions with different services to perform ‘as homeless’ based on the expectations of service providers. (Contributed)
Kelowna homeless forced to ‘perform’ for resources, says UBCO study

One participant in the study said ‘It is about looking homeless, but not too homeless’

Gov. Gen. Julie Payette takes the royal salute from the Guard of Honour as she makes her way deliver the the throne speech, Wednesday, September 23, 2020 in Ottawa. THE CANADIAN PRESS/Fred Chartrand
Gov. Gen. Julie Payette resigns, apologizes for ‘tensions’ at Rideau Hall

Payette, who is the Queen’s representative in Canada, has been the governor general since 2017

Grounded WestJet Boeing 737 Max aircraft are shown at the airline’s facilities in Calgary, Alta., Tuesday, May 7, 2019. WestJet will operate the first commercial Boeing 737 Max flight in Canada today since the aircraft was grounded in 2019 following two deadly crashes. THE CANADIAN PRESS/Jeff McIntosh
Passengers unfazed as WestJet returns Boeing 737 Max to service on Vancouver flight

After a lengthy review process, Transport Canada cleared the plane to return to Canadian airspace

The top part of the fossil burrow, seen from the side, with feathery lines from the disturbance of the soil – thought to be caused by the worm pulling prey into the burrow. (Paleoenvironntal Sediment Laboratory/National Taiwan University)
PHOTOS: SFU researchers find evidence of ‘giant’ predatory worms on ocean floor

Fossils found the prove the existence of an ancient Taiwanese worm as long as two metres

Most Read