Measuring behaviour with salt, light & air
Since 2009, the Victorian Wader Studies Group has been tracking the migration movements of Ruddy Turnstones on King Island using light-level geolocators. These ingenious devices weighing only 0.65g (1.2g once fitted to a small plactic leg flag) measure light-levels, conductivity and air temperature.
From these data, researchers from Deakin University are able to determine when the birds are in flight and when they are standing in salt water. They can even tell when and for how long a bird is incubating eggs from temperature and alternating light and dark signals.
Over the 10 year period, over 400 geolocators have been deployed. Geolocators are a much cheaper option for tracking migration when compared to satellite transmitters, which come in at 10 times the price. However, geolocators must be physically retrieved to obtain the data they hold within.
The nature of Ruddy Turnstones to return to the same site every year therefore makes them the perfect species with which to use this technology. So far, 206 of the birds fitted with geolocators on King Island have been receptured – a whopping success rate of 52% – some with multiple years of data.
One of these such birds is Ruddy Turnstone with orange leg flag, WMA, sexed as a male on plumage. Interestingly, unlike the other turnstones in this study, WMA has returned to the beaches of Newcastle on its southward migration for the past three years and has once again been sighted by the Hunter Bird Observers Group.