Saturday, August 27, 2005

When two separate flocks of geese, totalling more than 200 birds, were found dead in Manitoba farmer's fields, poisoning was immediately suspected.

But a newly published study has offered a stranger explanation: the geese may have become disoriented on dark and moonless nights and flown, en masse and at up to 100 kilometres an hour, into the ground.

The fowl were so unaware they were on a crash course for earth, they did not even have their legs extended for landing.

Researchers suspect the birds fell victim to something like the "spatial disorientation" that sometimes afflicts pilots and was blamed for the 1999 plane crash that killed John F. Kennedy Jr.

"I'd never seen it before," said Dr. Gary Wobeser, a veterinary pathologist at the University of Sasktachewan in Saskatoon, about the goose kills in 1985 and 2003.

"People often jump to conclusions when birds are found dead -- that they were poisoned.... It's important to look at it and find out what's really going on."

About 150 lesser snow geese were discovered dead in a corn field near Carman, Man., on April 10, 1985. Then on May 30, 2003, 62 Canada geese were found in a field seeded for spring wheat a few kilometres south of Winnipeg.

Poisoning was suspected, but necropsies done later revealed they had not eaten anything in the fields where they were found.

The examinations did find serious injuries, such as ruptured organs, fractured ribs and massive hemorrhage.

Most were lying on their breasts with their wings spread, and did not have the injuries that would be expected if they tried to extend their legs before landing.

"We believe that most of the dead birds died immediately," the paper said. "The force of impact of a goose weighing several kilograms collding in flight with the ground would be considerable."

Other research has clocked migrating goose flocks over Manitoba at an average of 76 to 106 kilometres an hour.

The night was clear but very dark, with minimal moonlight, in the 1985 incident. There was a thunderstorm and poor visibility the night of the 2003 mishap.

"They probably lost sight of horizon for some reason," Dr. Wobeser said.

Flights from a nearby U.S. Air Force base caused sonic booms the night of the 1985 crash, which could have prompted the geese to take evasive action, the paper also speculates.

The researchers compare the birds' confusion about their position in the sky to spatial disorientation among pilots. It usually occurs when weather or other conditions cause the aviator to lose sight of the horizon. Those who are not trained to fly solely with instruments -- about 80% of non-commercial pilots -- can lose perception of up and down. Unable to see the horizon, they must rely on the inner ear, but its sense of movement is prone to errors.

As errors build up, the situation can lead quickly to a "graveyard spiral," where the pilot loses control of the plane and it goes into a deep, diving spin. The pilot is usually unaware he or she is turning, believing the craft to still be flying straight.
http://www.canada.com/national/nationalpost/news/story.html?id=b0fe977a-0454-424a-b9cb-d3242ad92d1c