The work of a Simon Fraser University graduate student may have helped solve a bald eagle mystery on Vancouver Island.
Chris Gill, a master's student in biological sciences, has spent the last two summers studying bald eagles near Duncan, B.C. in an effort to find out why an alarmingly high number of nests are failing to produce healthy chicks.
The area of concern lies just south of the Crofton pulp and paper mill, and is part of a zone closed to fisheries in the 1980s due to high levels of dioxins -- toxic byproducts of the pulp bleaching process. Although the mill significantly reduced its dioxin output about 10 years ago, the bald eagles have failed to rebound. A 1995 study showed that three out of four nests in the closure zone failed, compared to an almost 100 per cent success rate for nests outside the zone.
"'Failed' means that there were eggs but they didn't hatch, or there were chicks but they died," says Gill. Dioxins seemed the most likely culprit, he says, yet that same 1995 study didn't find similar patterns near other coastal pulp mills. "This suggested that Crofton was different, but we didn't know why."
Gill looked to the eagles themselves for answers. He worked at two sites -- one near the mill, and the other, for comparison, on the west side of Vancouver Island near Bamfield. Over two summers he captured 24 eagles -- 10 adults and 14 eaglets -- and took blood samples to assess levels of pollutants such as dioxins, PCBs and DDEs (a form of DDT). He conducted aerial surveys by helicopter, counting the number of incubating birds and the number of nestlings produced. And he watched eagle nests, from dawn to dusk, for a total of 850 hours.
He also filmed eagle family life. With the help of a professional tree
climber -- eagle nests are typically 30-40 metres off the ground -- Gill mounted a
video camera above a nest and programmed a battery-powered VCR at the base of
the tree to record nesting
Contact: Marianne Meadahl
Simon Fraser University