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Above: Great Knots head off on the mudflats (Image G Chan)
Chris Hassell, from the Global Flyway Network, looks at new research into the migratory shorebirds that inhabit Roebuck Bay at this time of the year. The mudflats of Roebuck Bay in November are teeming with shorebirds that are well-adapted to the 40º temperatures, the mud itself being even hotter. They raise their back feathers (pilo erection) to let the heat escape. Birds like the Oriental Plovers and the Little Curlews do this constantly as they feed on insects and beetles on the grass plains. When it’s really hot, these birds move to and loaf around on the mudflats to stay cool.. Birds of prey regularly cruise over the bay at high tide, disturbing the shorebirds as they roost but they rarely attack unless they see a sick bird. There is also safety in numbers with all the different species taking to the wing at the same time, making any attack less likely to succeed.. The birds of prey don’t bother flying over the feeding birds out on the vast mudflats as they are easily seen from kilometres away and any attack has no element of surprise. There is still a regular banding program, marking individual birds with plastic flags and colour bands to build on the database of sightings, leading to a life history of each banded bird. There is also some satellite transmitter work using solar-powered backpack harnesses. This is being done on one of the larger birds, the Bar-tailed godwit, and on a medium sized bird, the Great knot. The Great knot is under enormous pressure, affected by the loss of mudflats in the Yellow Sea in China and Korea, so this satellite tracking will give a detailed insight into how individual birds use the Yellow Sea, Roebuck Bay and their distant arctic breeding grounds. The Great knots are fitted with handmade transmitters that only weigh 5gm, an innovative product of the company Microwave Telemetry. The transmitters are being used in an experiment into the personality of Great knots and its effects on their survival. It seems some Great knots are explorers, flying from one patch of mudflat to another when feeding. It is hoped that this behaviour will assist them when they fly the 6½ thousand km to China and find their mudflats degraded or gone, forcing them to search for other mudflats. Non-explorers will stay at that site, ‘making do’ or perishing. Scientific papers from Biijeveld et al from the Royal Dutch Institute for Sea Research are proving that the personality of some birds is driving their ecology. Some shorebirds only occupy particular parts of Roebuck Bay, colour banding showing a difference between the western and eastern areas. The transmitters will capture data at different times and those thousands of data points will build a database, giving detailed information about how individual birds use Roebuck Bay and the mudflats in China. Each bird also provides a blood sample, so gender and genetics can be added to the database.
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| Bar tailed Godwit being fitted with a satellite transmitter.
Image by G Chan.
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At present 12 Great knots and 13 Bar-tailed godwits are carrying transmitters and those birds will be tracked at Roebuck Bay, China and their breeding grounds in the Arctic tundra. It is this individual information which is adding exciting new insights to how shorebirds migrate southwards to Australia. One Ruddy Turnstone, fitted with a geolocator, migrated south through the Pacific. It went via the Aleutian Islands and the Marshall Islands before arriving back in Australia, an unexpected route. Some Red knots also make staged migrations south, while others fly the 10,000 km in one go. When the birds do migrate north from Roebuck Bay they fly in flocks of single species, with two exceptions. Chris Hassell has seen Asian Dowitchers mixed in with Bar-tailed godwits in a few flocks and also Grey Plovers with Bar-tailed godwits all observed from the Broome Bird Observatory. The v-shaped flocks mean the birds fly wingtip to wingtip, taking advantage of the turbulence and uplift, making their flight at least 30% more efficient by saving energy. The transmitter project was made possible because Professor Theunis Piersma won a Spinoza Prize from the Dutch Academy of Sciences, a prize worth 2½ million euros without strings attached. This has allowed the project to go ahead, a project on track to reveal a wealth of information about migratory shorebirds. It gives a positive meaning to the term track work.
Chris Hassell was interviewed for A Question of Balance by Ruby Vincent. Images from G Chan. Summary text by Victor Barry, December 2014.
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