Wader flock spooked by people
Similar species tend to have their own ‘patch’ when roosting. Photo: ©Tony Neilson

‘Pulsating jellyfish’ and the art of confusion

For the umpteenth time, the roosting flock of thousands of sandpipers suddenly took to the air and streamed out over open water.

‘They roll like a drunken fingerprint across the sky, smudging the … horizon with the quickness of a pulsating jellyfish,’ wrote the American Pulitzer prize-winning poet, Richard Wilbur.

He was describing a huge flock of starlings. But he could just as easily have been observing the aerial ballet I was observing recently on the exquisite turquoise and russet shores of Roebuck Bay near Broome on Australia’s northwest coast.

Readers should know by now that the Roebuck Bay Marine Reserve hosts one of the southern hemisphere’s biggest populations of migrating shorebirds – upwards of 150,000. They start arriving around September after breeding in the Arctic and stay until March-April before beginning the long flight north once again.

Off-season garb

During the early weeks following their return (or very first visit) to Roebuck Bay, the birds are exhausted, starving and suffering the strains of moulting as they change from their breeding array to a more somber off-season garb.

All they really want to do is to probe the bay’s vast, organism-rich mudflats for food. But they are forced to take breaks most days by the big tidal surges synonymous with the Australia’s Kimberley Coast. So, they gather in large, often species-specific flocks on sandy beaches and among rocks to ‘roost’ while waiting for the tide to again reveal the mud and its bonanza.

Incoming shorebirds to roost area
Thousands of birds driven off their feeding grounds by the tide will roost in tight groups for safety. Photo: ©Tony Neilson

Easy escape

The birds know they are vulnerable at this time and choose their roosting sites with considerable care: easy escape-routes being number one priority.

But despite the remoteness of the location, and its reserve status, their between-tides snooze at Roebuck is interrupted constantly by: raptors that cruise overhead looking for the weak or the unwary, fishers, birdwatchers, researchers, aircraft, drones, vehicles, tourists, and let’s not forget – photographers.

The need to roost securely is one reason why birds flock together. A larger group has a better chance of spotting a predator or another potential threat than a single bird has. Furthermore, a group of birds may be able to confuse or overwhelm a predator through mobbing or agile flight.

Confusion factor

Staying in a flock also presents a predator with the ‘confusion factor’, which lowers the total danger for any single bird.

It also seems there is an element of the ‘Keeping up with the Flockers’ that drives birds to readily copy the actions of others.

So how come they don’t crash into each other when swirling around like that? Good question and one that seems still to be challenging the sharpest scientific minds. Research on huge flocks of ‘murmerating’ starlings – millions of them – offers strong clues, including the fact that there is more space around each bird in the flock than may appear to the human eye.

But unravelling all the secrets of the little flockers remains some way off.

©Natural Images 2019

Sunrise 'staircase' at Roebuck Bay
Sunrise over Roebuck Bay can create spectacular effects – like this ‘staircase’. Photo: ©Tony Neilso
ABOUT THE AUTHOR

©2018 TONY NEILSON All Rights Reserved. All images are protected by Australian copyright law and cannot be downloaded or reproduced without my permission. Please contact me.

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