Ducks’ chemical signatures point to importance of Canadian delta

By Julia John

Biologists estimate 200,000 mallards migrate through the Saskatchewan River Delta in the fall.

Most people don’t know much about central Canada’s Saskatchewan River Delta, but new research analyzing chemical ratios in duck feathers highlights how this massive wetland between Saskatchewan and Manitoba serves as a critical stopover for hundreds of thousands of waterfowl migrating from northern Canada as they make their way to winter habitat in the United States.

“We view the delta as a funnel,” said Tim Jardine, co-author on the paper recently published in The Condor. “These birds are being pulled in from a large geographic range in northern Canada, funneling their way through and using this delta as an important feeding area before they head to the southern U.S.”

In 2013 and 2014, Jardine, an assistant professor at the University of Saskatchewan’s School of Environment and Sustainability, graduate student Christian Asante and fellow researchers examined the ratio of stable hydrogen isotopes in feathers from five species of ducks harvested on the delta. They focused on mallards (Anas platyrhynchos), American wigeons (Anas americana), pintails (Anas acuta), blue-winged teal (Anas discors) and green-winged teal (Anas crecca). These waterfowl were selected because of their importance to the culture and livelihood of the residents of the nearby community of Cumberland House, who provided specimens for the researchers to study.

“Stable isotope ratios are natural fingerprints that animals pick up through their diet and water,” Jardine said. “Birds acquire this isotope ratio in their feathers and take it with them where they go. We can pluck a bird’s feather, test the hydrogen isotope ratios and figure out where it grew that feather.”

Ducks Unlimited and the U.S. Fish and Wildlife Service had long recognized the delta as key waterfowl habitat, and BirdLife International designated it an important bird area because of the enormous number of birds congregating here, Jardine said, but it had been overlooked by researchers. Biologists knew it was important for birds that had hatched on the delta, he said, but the research revealed that it was also critical to migrating birds from all over northern Canada. The majority had hatched outside the delta, not within it, as the researchers had presumed.

The 10,000 square-kilometer delta faces pressure from upstream dam construction, which changes the flow regime and decreases the summer floods that soak the wetlands so that they can support birds arriving in the fall, Jardine said.

“We can make sure the delta is well looked after so it will provide habitat for birds coming from such a large area,” Jardine said.  “Anyone who likes to look at birds should be thankful to this place because not only does it provide stopover habitat, it’s also important breeding habitat.”

This study also showed that the technique can be an effective means for wildlife managers to trace bird origins, Jardine said, adding to information gained from banding, although unlike banding, the isotope approach can only point to a general area where the birds came from.

Jardine’s team plans to assess stable isotopes in other species that rely on the delta as a stopover site, such as shorebirds, to find out where they’re migrating from.

Julia John is a science writer at The Wildlife Society. Contact her at jjohn@wildlife.org with any questions or comments about her article.

Read more of Julia's articles here.