|Bar-tailed Godwit. ©JARI PELTOMÄKI/VIREO|
The Bar-tailed Godwit is a large shorebird (very similar to California's Marbled Godwit) that breeds on the tundra, from Alaska east to Scandinavia. Of particular interest to our research group is the subspecies that breeds in northern and western Alaska, Limosa lapponica baueri. Following breeding, this bird stages (prepares for migration) along the coast of western Alaska, from the Yukon-Kuskokwim Delta down to the Alaska Peninsula. In September and early October, after gorging on clams, marine worms, and other food--and then carrying the greatest fat load of any migrant bird known (having doubled their body mass)--these godwits head east and south out over the Pacific Ocean. Some fly continuously for ten straight days, covering more than 11,000 kilometers (6,600 miles), the longest migration of any shorebird. Their destination is New Zealand or Australia, where they spend their winter season.
|PHOTO ©IAN HUTTON/VIREO|
One thing we want to learn more about is how these birds migrate back to Alaska from New Zealand. From past studies by others, it appears that birds may fly north from New Zealand in late February through April, some then stopping in Australia, others in New Guinea, before they continue on to sites in China, Korea, Japan, and eastern Siberia. Finally, by early May, they cross over to Alaska to breed.
The use of PTTs will greatly aid our efforts to understand how these shorebirds move through their global landscape. The transmitters beam a signal to a series of orbiting satellites, where the bird's location is plotted and the information beamed back to a company in France. Via computers, we get the daily locations of tagged birds, which we will use to map out their migration routes over about half the world.
A problem we face is getting the transmitter tag to stay on the bird over the time and distance of its travels, such that it does not interfere with the animal's behavior. One technique we can use is to implant the transmitter in a bird's body cavity. Our research group includes one of the most experienced teams in the world for implanting PTTs in birds (expert veterinarian Dan Mulcahy of USGS in Alaska and shorebird biologist Bob Gill). We will also try out a solar-powered transmitter, attached to the bird with a harness. These radios have the advantage of being lighter and lasting longer than PTTs but are unable to transmit as many locations daily. Learning how to obtain the information we seek is clearly a big part of the research endeavor.
This new telemetry study of large, far-traveling shorebirds will continue beyond my winter field stint Down Under. In April and May of this year, PRBO will work with others on tracking Long-billed Curlews from their breeding grounds in the western United States to wintering grounds in California and Mexico. In June, colleagues in western Alaska will put satellite tags on Bristle-thighed Curlews to better understand that species' migration to the far Pacific Islands. Next winter, we hope to put PTTS on Hudsonian Godwits in southern Chile.
In two years time we aim to be able to map all the tracks of these far-ranging godwits and curlews. I predict a criss-cross pattern connecting locations throughout the Pacific Basin in amazing and intricate ways.