June 17, 2009

World’s Oldest Raptor Nest Discovered

Scientists have uncovered a bird's nest believed to be 2,500 years old on a cliff in Greenland. The discovery is the oldest raptor nest ever recorded, and the site is still in use today by gyrfalcons, the largest falcon species in the world. Three other nests, each over 1,000 years old, were also discovered, one of which includes feathers from a bird that lived more than six centuries ago.

But ornithologists worry that climate change could soon drive the falcons from these ancient sites.

Gyrfalcons live near the Arctic, ranging in color from nearly all white in Greenland to nearly all black in Labrador in Canada.  Instead of constructing nests out of twigs and sticks, they lay eggs in circular depressions they create in existing ledges or old nests made by other birds. 

While stick nests are frequently damaged, precluding their repeated use, gyrfalcons often revisit some ledges and potholes year after year.

To determine how long the birds return to the same site, University of Oxford ornithologist Kurt Burnham and his colleagues carbon dated the guano and other debris that birds leave behind at various nest sites in and around Greenland.

Greenland's cold, dry climate slows the decomposition of the falcons' droppings, with some nest sites having levels of guano nearly 6 feet deep.

Nevertheless, Burnham was still surprised to learn just how old these nests are.  Indeed, one in Kangerlussuaq in west-central Greenland is between 2,360 and 2,740 years old, the carbon dating revealed. Three other nearby nests are more than 1,000 years old, the youngest of which was first occupied 520 to 650 years ago.

The gyrfalcons still routinely use these old nests today.

"While I know many falcon species re-use nest sites year after year, I never imagined we would be talking about nests that have been used on and off for over 2,000 years," BBC News quoted Burnham as saying.

Burnham's team also found interesting clues about the past inhabitants from within the nests, with three feathers discovered within the 13 nests the researchers had sampled.  The youngest feather was 60 years old, while the oldest was from a falcon that had visited the next nearly seven centuries ago.

The old guano samples provided clues about what the birds had eaten centuries ago.  For example, gyrfalcons living in the central-west part of Greenland, which is closer to the ocean and further away from the Arctic ice sheet, had diets with much more marine animals. Meanwhile, falcons living further to the north in closer proximity to the ice ate much more terrestrial prey, such as arctic hare.

"These findings put new emphasis on just how important nest site characteristics can be for raptor species, particularly large raptors," said Burnham.

"Something, be it nest ledge depth, or the amount of cliff overhang above the nest, is so attractive at these locations that gyrfalcons are re-using them for thousands of years."

The fact that gyrfalcons tend to return to certain sites for hundreds of generations suggest they may be particularly susceptible to climate change, according to Burnham.

"As a result of a warming and ameliorating climate other bird species, such as peregrine falcons, are moving further north."

"As peregrine populations continue to increase in density they will likely use more and more of these traditional gyrfalcon nests, forcing gyrfalcons to find alternate locations to nest in which may not offer the same amount of protection from the harsh Arctic environment in Greenland."

Similar research has revealed when entire colonies of birds initially took up residence at certain sites. Using carbon dating of solidified stomach contents, peat moss deposits and bone and feather samples from a number of moulting sites, scientists discovered that colonies of snow petrel have returned to the same nesting sites for 34,000 years, and adelie penguins for 44,000 years.

The research was reported in the Ibis International Journal of Avian Science.


Image Credit: Wikipedia


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International Journal of Avian Science