With sun beating down and humidity increasing, we drip with sweat, crouching uncomfortably under the scant shade of a eucalypt with flies nibbling our legs.
Up ahead, on the fiery red cliff fringing the sparkling waters of Roebuck Bay, Broome resident Chris Hassell sits in a makeshift camouflage tent, binoculars trained on an explosives-laden 20m cannon net concealed on the sand.
Everyone else – a motley crew of local volunteers and scientists – sits metres behind, sucking on watermelon rinds or knitting, trying to be quiet.
Just before noon, after hours of waiting, Hassell’s voice finally crackles over the walkie-talkie: “No catch.”
Everyone sighs, folding away their camp chairs. They’ll be back again tomorrow, just after first light; all this to net a few tiny birds.
Members of the Victorian Waders Study Group have been visiting Roebuck Bay at least twice a year since 1981; the stunning 15km slice of coastline along Broome is a vital resting and feeding ground for an estimated 150,000 migratory shorebirds undertaking an extraordinary round trip to the Arctic every year.
In 2008, a Bar-tailed Godwit fitted with a satellite tracker by the Global Flyway Network was discovered to have flown non-stop from Broome to South Korea’s Yellow Sea in April – 5870km journey.
After refuelling, it flew 4800km to Siberia and then on to its remote islands – an additional 1100km – before stopping to breed in the Arctic.
Weeks later, it flew back to the Yellow Sea (4400km) Flores in Indonesia (4200km) and on to Broome (1500km) in September – a staggering 21,870km round trip.
With recent advances in technology, the group and Australasian Waders Study Group have now turned their attention to other migratory birds too tiny to be fitted with satellite trackers.
Since 2010, 60 Greater Sand Plovers, six Great Knot and 44 Red Knots have instead been fitted with “geolocators” – tiny, light-sensitive devices weighing less than a gram.
By recording changes in light intensity every 10 minutes, they reveal an extraordinary amount: where the birds go, how fast they get there and what they do when they arrive.
Collecting months of data, they build a map of the bird’s journey. Volunteers can even tell when the bird is incubating eggs in the Arctic; it goes dark for days on end when it sits on the nest.
During September and October, when the birds arrive back in Broome to gorge on mudflats teeming with protein-rich food to almost double their weight ready for their next journey – the volunteers are lying in wait.
Roz Jessop, Victoria’s Phillip Island Nature Park environment manager, says the birds are fascinating in their own right, but there is a serious aspect to the work.
In the East Asian-Australasian Flyway, infilling of vast estuarine tidal flats fringing the Yellow Sea to make way for industrial development has destroyed critical feeding grounds, threatening the survival of species.
About 40 per cent of the inter-tidal mudflats have disappeared in the past 30 years, and conservationists are finding a corresponding decrease in bird numbers.
“Most of these birds from Broome go through the Yellow Sea, where reclamation is just progressing really, really quickly,” Dr Jessop says.
“If the spot where they have to stop off and refuel is not there, people think they can go somewhere else – but of course all the other birds are there already … most places are carrying the maximum number they can.”
With other worldwide habitat disappearing, Roebuck Bay – one of 64 Ramsar wetland sites in Australia protected under the Federal EPBC Act – is considered to be among the most important migratory shorebird sites left in the world.
In February and March, a big international contingent joins the Australasian group for a second annual trip to Roebuck Bay and Eighty Mile Beach further to the south, to which an estimated half a million birds flock every year.
For now, the coastline is relatively pristine; Broome’s Yawuru Aboriginal rangers play an active role in cleaning the beach, conduct water quality testing and mud sampling to measure the effects of nutrient run-off into the bay.
For now, food is plentiful and visiting birds feed for hours each day, retreating at high tides onto sandy beaches and rocky outcrops – perfect for bird-spotting.
Already, the groups have re-sighted 18 Red Knots returned tagged with geolocators, along with all six tagged Great Knot and 50 tagged Greater Sand Plovers – but catching them is another matter.
Looking frustrated, Mr Hassell tramps over from the bird hide. It’s been a disappointing morning.
“We had a Black Falcon, a powerful falcon, straight over the flock a couple of minutes before we hoped to fire and catch some birds,” he says.
With high tide threatening to swamp the 20m net, he resorted to using plastic birds as decoys to attract live ones; perhaps sensing something was up, they stayed away.
Mr Hassell, a volunteer also paid by the Global Flyway Network to monitor shorebirds, is baffled; expecting to find up to 30,000 birds on the beach at this time of year, he has seen only a few thousand – the least in his 16 years studying the bay.
“It’s a complete mystery to me; it’s possibly the falcons but even that shouldn’t be enough to cause such a change,” he says.
“It’s confusing to say the least … the beaches should be thronged with birds and they’re not.”
Early the next day, volunteers resume their spot under the tree while spotters hit the beach for a bout of “twinkling” – gently moving flocks of birds so they fly to the net.
Some birds with tell-tale orange flags are flying around but by 10am, the mood is already gloomy.
Helicopters and planes have flown incessantly overhead and flocks have been sent fleeing by circling Brahminy Kites and Sea Eagles.
Surveying the coast, statesman-like, is a man widely regarded as one of the world’s migratory bird experts – Dr Clive Minton, a former metallurgist based in Melbourne who has visited Broome up to three times a year since 1981.
Cheery and loud – he’s almost stone deaf – Dr Minton says he’s been fascinated by the birds “since I was hatched” and has conducted scientific surveys since he was 12.
“There’s still a lot more we don’t know, but by developing techniques for catching them, marking them with bands and coloured leg flags and more recently geolocators, we’re gradually unravelling the details of their migration strategies,” he says.
“Each time there’s a step forward in technology, you learn an awful lot more.”
He says when gelocators were developed to a size tiny enough to fit to the birds three years ago, knowledge about them suddenly surged; they discovered, for example, that Greater Sand Plovers breed in the Gobi Desert in Mongolia, north of China.
The big disadvantage, he says, is that birds fitted with the device have to be recaptured to download the data.
“This is our third day in the field trying to catch Greater Sand Plovers we can see on the beach carrying our gelocators – can we get them in the right place at the right time … not yet,” he says. “It’s very frustrating.”
Down on the beach, Mr Hassell resumes sticking plastic decoys in the sand. Within seconds, a Brahminy Kite swoops and snatches one up, eliciting sniggers from onloookers.
Giving up, Mr Hassell strides over. “I tell you what,” he says. “Why don’t I give you a ring when we actually get some birds.”
The next day, the phone rings about 10am. This time, Mr Hassell is jubilant: “Get down here as quick as you can,” he says.
At the beach, volunteers buzz around underneath a big shade cloth tent erected in the sand, weighing and measuring birds as others wait their turn safely ensconced in dark shade cloth “keeping cages”.
Dr Minton is beaming: about 70 birds from six species have been netted, including two Greater Sand Plovers tagged in March 2011.
“We finally hit the jackpot,” he says, holding a placid specimen weighing about 70g in his hands.
“Both of those birds would have been to the northern hemisphere and back in 2011 and they’ll have been back there again in 2012 … we hopefully will get a round-trip migration for at least one season.
“Previously, before putting geolocators on, we had no information about where they bred at all, no information about where they went once they reached the Vietnam coast – there was nobody inland there to find flags or metal bands on birds.”
After spending hours trying to catch the birds, they release them very quickly; within minutes, old geolocators are removed and new ones fitted and within four hours after high tide, all birds are released to feed on the mudflats; untroubled by their ordeal.
Dr Minton said systematic counting had shown a visible decline in bird numbers in recent years and it was becoming a real worry: “About half the migratory species in Australia have declined by anything between 30 and 80 per cent,” he says.
“In all cases, those are species using the tidal shores of the Yellow Sea in China and Korea as the key stopover site to fatten up on their northward migration to their breeding grounds in the Arctic and southward migration back to Australia.”
He says getting hard data on the birds’ migratory patterns is the best way to convincing governments in Australia and overseas to preserve key areas of land.
“That loss of feeding habitat is the cause of the decline of those species – that’s the facts,” he says.“Shorebirds in this flyway are in more of a predicament than they are in any other flyway anywhere else around the world. Things like that need to be understood and then rectified – that’s what we’re about.”