Our guest contributor Ben continues his story from last week…
We had now spent months observing and monitoring these juvenile Banded Stilts as they grew from eggs to nearly-fledged birds in one of the harshest environments on earth. The newest generation was finally old enough to be banded.
It is one thing to observe where birds nest but the real mystery of waders is where they go and how they move when they’re not breeding. A cheap and easy way to track wader movements is to catch them and apply a coloured leg flag. The combination of colours indicates where and when the bird was banded. Birds are still being recorded that were banded more than ten years ago. Birds banded in the Coorong have been spotted at Avalon Saltworks in Victoria and as far away as Yalgorup National Park in WA!
When the time is right, adult birds lead newly hatched chicks off the nesting island and spread out across the shallow water. As winds build across the bare surface of the lake, the water is blown around. In one instance, I walked hundreds of metres through ankle deep water and on returning to my starting point only an hour later, the water was gone. Thousands of stilts move with the water making it a daunting task to try and predict where they’ll be and how to catch them for banding.
As the scheduled banding dates drew near, a flight over Lake Torrens bore bad news. The stilts were spread far and wide at distances that made getting to them for banding near impossible. We had to postpone the trip. But with every week the chicks grew closer to fledging and opportunities were running out.
A short time later, the plane was sent up again. This time the Stilts were co-operating and were seen in areas relatively close to the shoreline. Our eager group of 5, lead by expert bander Maureen (of Friends of the Shorebirds South East), set off to band as many birds as possible over 5 days.
For weeks prior, we had discussed how to catch the birds. Nets were painstakingly designed to herd the birds into and, in theory, make them easy to catch. In practice, stilts came within centimetres of the net at which point they’d jump over the top and keep going. It looked like we’d need to find another way to catch the birds.
So we took dab nets and banding gear and headed out toward the invisible horizon where the shallow water reflected the sky and at times made it appear that we were walking through the clouds. The next few days were spent (once again) getting covered in salt and mud. But more importantly, by the end of it 332 immature stilts were sporting orange and yellow leg flags!
Two weeks later we returned to determine the fate of the colony. As water evaporated the massive increase in salinity had killed off the brine shrimp (and all other life in the water) and all the birds that could fly were gone. Amazingly, the majority of immature birds fledged in time to move off and find food elsewhere.
So how do the birds know when it rains in the desert from hundreds of kilometres away? And how do they know that the water won’t evaporate before all the young birds can fledge? The long flight, breeding and laying up to five eggs soon after arriving represents a massive energy investment for an exercise that seems so fraught with the potential for failure. Finally, where do all the young birds go?
The answer to the last question is something you can help with. If you happen to see a Banded Stilt in your neighbourhood, make sure you look closely and take note of any coloured leg flags. Report the leg (left or right), colour and shape to the Australasian Wader Studies Group.
The table below lists the leg flag combinations for banded Banded Stilts:
|1995||Lake Ballard, Vic||Single yellow, right upper leg|
|2000||Werribee, Vic||Single orange, right upper leg|
|2006||Coorong, SA||Orange above yellow rectangular flags, right upper leg|
|2010||Lake Torrens, SA||Orange above yellow rectangular flags, left upper leg|
|2011||Lake Torrens, SA||Orange above yellow triangular flags, left upper leg|