Analysis of isotopes in waterfowl feathers is increasingly informing scientists about bird movements and may help wildlife biologists in efforts to improve duck and goose harvest regulations. The isotopes show unique signatures in feathers and indicate the birds area of origin. (Photo: Courtesy of Wisconsin Department of Natural Resources)
Tagging animals is among the oldest and most valuable techniques in wildlife management.
Before its use, many questions could only be met with guesses. Where does a species migrate? What is the size of the animals’ home range? Do they have fidelity to a breeding site? How long do they live?
According to historical accounts, the first record of bird banding occurred in 1595, when a peregrine falcon owned by Henry IV of France flew off after a hawk and turned up 1,350 miles away.
John James Audubon is credited with the first such activity in North America; he placed silver cord on a brood of phoebes in 1803.
Over the last century the practice has proven particularly important in the field of waterfowl management. The U.S. Fish and Wildlife Service has more than 70 million banding records on file, with most since the 1960s but some dating to 1914.
Any state that offers a hunting season for a migratory species must participate in banding. The information from band returns on hunter-killed birds is used to help protect populations and guide decisions on bag limits and season dates.
The technique has known limitations, however.
It’s not possible to tag ducks in all production areas, for example, leaving gaps in the database. And unless a bird is banded at a very young age, it’s not known where it was hatched.
But a promising new technology has come on the scene that could be a game changer for wildlife managers.
It’s being referred to as a “stable isotope approach” to determining where a bird was hatched or molted.
Drew Fowler, migratory game bird research scientist with the Wisconsin Department of Natural Resources, dedicated a portion of his presentation to isotope tracking at a Aug. 31 waterfowl meeting hosted by the Wisconsin Wildlife Federation.
As birds hatch, eat and grow, the water they consume produces a unique signature of hydrogen isotopes in their feathers, Fowler said. The same is true of adult birds that settle in an area to molt.
Scientists have mapped gradients of these isotopes called a feather isoscape across latitudes in North America, sort of like stripes on a honey bee.
“It’s early, but it looks like this could be really helpful as we seek to constantly improve our understanding of where birds originate and where they are harvested,” Fowler said.
Matthew Palumbo, a researcher with Western University in London, Ontario, is the lead author on two papers published on the technique in the last year.
That work, conducted in Ontario on mallards and blue-winged teal, revealed some striking differences from long-held beliefs about the origins of hunter-killed birds.
In a nutshell, the hunter harvest was made up of a much lower percentage of locally-produced birds than indicated from decades of banding data.
For example in the mallard study, only 3% to 22% of birds killed by hunters in southern Ontario were produced locally, whereas wildlife managers expected it to be well more than half.
Most of the harvested birds were from areas of Canada farther north and west of the sites they were killed.
Would work in Wisconsin produce similar eye-opening results?
“We’re always looking to use the best science we can,” said Taylor Finger, DNR migratory bird ecologist. “We will definitely be looking at ways to incorporate this into our management.”
Since waterfowl biologists attempt to protect local populations from overharvest, the information is very important.
About 200,000 ducks are banded annually in North America, and 90,000 bands are reported. The band returns are important for wildlife managers as they study harvest and survival rates and develop waterfowl hunting regulations.
Banding will likely always play a role in wildlife science.
But since it is labor intensive in the best of circumstances, and impossible in others, the isotope analysis could portend a new era, especially in waterfowl management.
The isotope technique has multiple advantages. It only requires a feather be turned in from a bird, dead or alive, and never requires the bird to be trapped and banded.
Among its disadvantages is its lack of specificity. The feather isoscapes are more than 100 miles wide in most areas.
Still, it represents an exciting potential for waterfowl managers.
The Wisconsin DNR is on the cutting edge of using the technology.
Finger said the agency is developing a library of isotope data from birds known to nest in the state, including mallards, wood ducks, blue-winged teal and ring-necked ducks. It will then analyze feathers from birds harvested by hunters to learn where the birds originated.
“For years we have made the assumption based on band recoveries that 70% of mallards we harvest in Wisconsin were produced in Wisconsin,” Finger said. “This new work may lead us to a whole new understanding of where the birds are coming from.”
I tip my cap to Finger, Fowler and the rest of the DNR waterfowl staff for keeping their eyes open for new technology and, when opportunities arise, continually improving their management techniques.
More on waterfowl
For the second consecutive year Mark Kakatsch, Wisconsin Wildlife Federation migratory committee chairman, organized a waterfowl summit in late August. Due to the coronavirus pandemic, this year the meeting was held virtually.
In addition to Fowler, it included presentations by Finger, DNR chief warden Casey Krueger and Bruce Ross, executive director of the Wisconsin Waterfowl Association.
Freelance outdoors writer Tim Eisele, Wisconsin Conservation Congress member Paul Gettlefinger, WWF executive director George Meyer, Ducks Unlimited member Nels Swenson and I were among those who participated.
I’ll have coverage of other topics from the meeting, but here are a couple of nuggets: Finger said Wisconsin and the other states in the Mississippi Flyway have requested a five bird daily bag limit for Canada geese, possibly to begin in the 2021 season; and a Wisconsin waterfowl expo is being planned for August 2021 in Oshkosh.