Solving the Riddle of One of the World’s Heaviest Flying Birds
Mimi Kessler's studies reveal the surprising migration of the elusive Asian great bustard.
At 40-plus pounds, great bustards are among the heaviest birds that fly. Despite their size, researchers know little about the movements of the Asian subspecies. In part because they're so difficult to catch--get closer than a half-mile and the grassland dwellers take off. But Mimi Kessler, a doctoral candidate at Arizona State University and founder of the non-profit Central Asian Great Bustard Project, and Mongolian colleagues managed to trap three nesting females and affix satellite tags. Turns out, their migrations cover more than 2,000 miles between their northern Mongolian breeding grounds and Chinese wintering grounds--twice as long as previously thought, they report in the Journal of Avian Biology. Kessler spoke with Audubon about these marathon runners of the bustard family.
Why don't Asian great bustards get much attention?
There's been very little research done on this bird in this part of the world in part because of lack of scientific capacity. Mongolia is a country the size of Western Europe but there's only 6 professional ornithologists working there. It's also a country with very little infrastructure, so travel is incredibly time consuming. Additionally, this is a bird that's extremely wary of humans. Typically, it moves away form you before you can observe it with the naked eye. On average, we captured just one bird per every month of work. So it's not a bird that's easy to study.
Tell me more about great bustards.
Great bustards display the largest sexual size dimorphism seen in birds. Males can weigh a maximum of 44 pounds, or up to four times the weight of females. This bird is also a lekking species. The males gather annually at a traditional spot to perform an amazing, elaborate breeding display. The females then chose between the males. So apparently sexual selection has led to males being much larger than the females--that's their preference.
What are the threats to Asian great bustards?
Through satellite telemetry we've been able to identify and are beginning to quantify some of the threats to the birds. We're finding that hunting for both meat and out of curiosity is a major problem for this species. Since this is a rare bird that travels rather unpredictably and doesn't follow set stopovers, sometimes people will shoot it in order to examine it more closely if it's the first time they've seen an individual of this species.
There's also hunting for sport that's carried out by people from the Mongolian capital or provincial centers. Typically, groups of bureaucrats or businessmen come out with other well-to-do people for a bonding-type sports hunting trip.
In China, we found that individuals target this bird for selling the meat in wild food restaurants. These wild food restaurants are illegal, but they continue to operate in many parts of China.
Through your research you found that Asian great bustards migrate more than 2,000 miles. What else did you learn about this subspecies?
One thing is the unpredictability of their movements. We're used to thinking of conservation of migratory species in terms of the paradigm of migratory waterfowl. If we protect certain key lakes that waterfowl always stop over at, we'll be able to successfully protect them as they migrate south or north. But Asian great bustards are grassland birds that aren't dependent on specific habits per se. We haven't seen repeated stopovers between a single bird over the course of multiple seasons or years. This makes conservation planning much more complicated.
We suspect the birds undertake such long distance movements because they're trying to escape severe winters. In northern Mongolia, the average winter temperature is about minus 30 Celsius, though it can get down to minus 40 or 50. Over course single summer day the temperature there can vary by as much as 20 degrees Celsius. So these birds are under much different pressures than the birds in Europe. We suspect that these birds, in addition to their migration, may have other adaptations to deal with the severe cold. We're carrying out genetic research now to look at the degree of differentiation between the European and Asian subspecies.