Boom time for migratory birds in Australia

By Natsumi Penberthy 8 August 2012
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A few wet years have brought tens of thousands of migratory birds to NSW wetlands.

IT IS ONE OF Mother Nature’s spectacular sites – enormous flocks of migrating birds coming in to land, exhausted from their long journey and needing to rest and refuel.

This year one of our wetlands of international significance – Narran Lake Nature Reserve, about 60km south west of Lightning Ridge in NSW – was the site chosen by straw-necked ibises.

By the tens of thousands, they trampled lignum, a spindly shrub that sticks up out of flood waters, forming floating pontoon neighbourhoods of nests. 

It’s the fourth year that rains have travelled through the Condamine-Balonne River system to the Murray Darling Basin, triggering a straw-necked ibis breeding event at Narran wetlands.

“Narran would be one of the best wetlands, certainly in the Murray Darling Basin, and in Australia, for colonial nesting water birds,” says Robert Smith, the regional manager of Northern Plains National Parks and Wildlife Service.

The impact of drought and irrigation on wetlands

Four years ago, concern about these straw-necked ibises was at its peak. These migratory birds live of average eight to 10 years, breeding opportunistically in wet years.

When rains in 2008 led to the first breeding event since 2000, after a decade of drought, concern was raised about the possible abandonment of fledglings as waters dried up. The Murray-Darling Basin Commission intervened and agreed to fund a $2 million acquisition of water supply to supplement Narran’s wetlands – a resounding success possibly saving up to three-quarters of the chicks.

Subsequent good years have created a healthy, multigenerational population of birds. “It’s a phenomenal spot…particularly where it has been quite wet through parts of the Murray Darling Basin,” says Rob.

In 2008 there were about 70,000 nests at Narran Lake – a big year. Each subsequent year has increased in the order of 20,000 nests – each attached to a mating pair of birds. It means that during a breeding season between 40,000-140,000 birds jostle for space on the 8447ha park.

Documenting the Narran bird wetlands

Despite the prettiness of this flurry of feathers, the reserve isn’t open to the public and only researchers have access, due to its significance as a breeding site and drought refuge for waterbirds.

The straw-necked nesting site itself is compact because the birds nest quite closely, occupying less than 100 hectares, explains Rob. “They nest out in the water because it protects them from predators,” he says. 

It’s an incredible community to see, which is why national parks invited photographer Josh Smith to document the ‘flood pulse’ from a helicopter in March. 

“It’s like a little urban community springs up, full of birds, and what happens is other species tend to come and sit inside the nesting site,” says Rob.

A range of species can be seen alongside the straw-necks, he adds, including  royal spoonbills, wide ibis, pied cormorants, great cormorants, darters, and nankeen night herons.

Josh, who spent most of his time up in a helicopter documenting the ibises says “watching the straw-necks soaring on the thermals means sometimes you’ll be 300-400ft up in a chopper and they’ll be above you.”

“The locals tell me that pelicans also come here to die, but you’ll also see baby pelicans – it’s an interesting life and death thing,” he says. 

The mystery of wetland birds

Despite ongoing research, the habits of migratory birds are something of a mystery. “There’s lot of different theories about what are the cues that bring birds into these large colonial events,” says Rob. “It is felt that there are sort of landscape triggers,” says Rob.

“When they’re quite mobile and migrating they can see the landscape cues [and] they can see the waterholes linked up through river paths and they’ll follow that to their site. One of the curious things is they tend to go back to exactly the same sites every time, I mean exactly the same sites…same spot,” he says.

It’s still not entirely understood where they disperse to after the breeding event. They’re probably dispersing up to northern Australia, following resources, says Rob.