Where have all of the scaups gone?

Hey there, time traveller!
This article was published 20/01/2008 (6756 days ago), so information in it may no longer be current.

A recent acute decline in two closely related Manitoba duck species remains unexplained. The lesser and greater scaup are widely distributed diving ducks whose steep continent-wide population losses are so substantial that they warrant significant worry. Western Canada is the North American breeding hub for both species.

“The decline in continental scaup numbers continues to be of great concern,” said Jane Austin, a U.S. Geological Survey scaup specialist based at Northern Prairie Wildlife Research Center in North Dakota. “Estimates show record-low numbers since 1999.”

The combined decline of both scaup species is especially substantial in Manitoba. According to breeding ground surveys conducted jointly by the Canadian Wildlife Service and the U.S. Fish and Wildlife Service, there has been a 49 per cent scaup decline in southern Manitoba, and a 56 per cent loss in northern Manitoba in the past four decades, but primarily since 1989.

Combined scaup population data derived from continental mid-winter counts, breeding ground surveys and Audubon Christmas bird counts, suggest a population decline from about six million scaup to roughly three million in the past five decades. The most substantial losses have taken place in lesser scaup; five million down to 2.5 million. The National Audubon Society lists the greater scaup as one of the 10-most declining species in North America, with an estimated 75 per cent population loss in recent decades.

“Lesser scaup populations have not responded to improved breeding conditions in the past few years in western Canada,” said Kathy Dickson, a senior Canadian Wildlife Service biologist based in Hull, Que. “The breeding population is about 50 per cent of the population goal.”

Preliminary data suggests that reproduction failures might be at least partly responsible. According to USGS figures, juvenile recruitment in lesser scaup has fallen in North America by 10 per cent per decade since 1970. U.S. Fish and Wildlife Service biologist Robert Smith has estimated that banding data shows scaup juvenile mortality rates are 70 per cent per year, a substantial portion of which is due to hunting loss.

Scaup hunting has been permitted in Canada under the Migratory Birds Convention Act since 1918. Canadian Wildlife Service harvest surveys reflect the magnitude of the scaup decline in recent years. Data accumulated by Jean-Francois Gobeil shows greater scaup harvest in Canada has fallen from 44,000 in the 1970s to 8,500 at present; the lesser scaup harvest declined from 108,000 to 32,000 in that same period.

“We have not yet felt that harvest is driving a population trend,” Dickson explained. “We don’t think that either scaup species would particularly benefit from restrictions to Canadian hunters, but we continue to evaluate.”

The USFWS agrees. “We acknowledge that the decline in scaup is most likely driven by large-scale changes in environmental conditions, but smaller populations have less harvestable surpluses.”

So far, however, the scaup decline has not been specifically linked to habitat changes or to climate change.

According to wildlife toxicologist Birgit Braune of the National Wildlife Research Centre in Ottawa, “levels of concern” of mirex, photomirex, polychlorinated biphenyls and other contaminants have been confirmed in scaup in Canada, but so far it is not clear if contaminants impact on scaup survival or reproductive success.

Hydroelectric initiatives involving major river diversions in northern Canada also are of concern because they could significantly impact on critical scaup breeding habitat, according to David Trauger, a scaup specialist at Virginia Polytechnic Institute.

“Most major northern Canadian rivers are slated to diversions, and since greater scaup seem to focus their breeding activities at the mouths of these rivers, any habitat changes could impact directly on the scaup. The Churchill River diversion is a case in point.”

Preliminary data suggests a 50 per cent greater scaup breeding population loss in the Churchill area since the Churchill River was diverted. The reasons are unclear.

Scaup are late-nesting waterfowl. Ongoing research in northern Manitoba indicates that increased intensity of mosquito harassment has resulted from warming summers and that the onset of such harassment has significantly advanced to encompass the entire incubation period for nesting scaup. Biologists suspect that such harassment might be responsible for substantial nest desertions by incubating female ducks since severe blood loss can be debilitating, and in some cases, fatal.

Robert Allison is a Victoria-based wildlife

biologist and writer with a PhD in zoology. He has been conducting research in Churchill since 1969. In 2002, the Humane Society of the United States commissioned him to write a report on the scaup.