By Tina Yerkes, Ph.D.

As the old saying goes, you are what you eat. Of course, the same is true for waterfowl. But the bodies of ducks and geese also contain hidden clues about where they eat. By analyzing feathers, blood, and other tissue samples, researchers are able to learn much about the habitat preferences and movement patterns of waterfowl.

The science behind this fascinating and relatively new field of waterfowl research is similar to what you might see on an episode of the popular TV series CSI. But instead of analyzing evidence to track down a murderer, waterfowl researchers use an intriguing combination of chemistry and ecology to trace bird movements over large geographic areas.

Stable isotope analysis helps researchers unravel patterns of movement at geographic scales not previously possible. The inability to track birds as they migrate from breeding grounds to wintering areas and back again has left large gaps in our knowledge of many species. Traditional radio telemetry or leg band returns have limited utility because of the large distances covered by many birds and their use of remote habitat. And some species are rarely banded or harvested. Although satellite telemetry is filling some of those gaps, stable isotope techniques are the newest tool in the waterfowl CSI toolbox.

Stable isotopes are naturally occurring forms of elements such as nitrogen, carbon, and hydrogen, which combined with oxygen produce water. As birds and other animals feed, stable isotopes are incorporated into their body tissues. Isotopes are specific to geographic areas or feeding conditions. Therefore, isotope “signatures” in body tissues can place a bird in the location where it grew a specific body part, such as a feather or toenail. For example, ducklings grow their flight feathers soon after hatching and then fly south. If you sampled a flight feather from a hatch-year bird on the wintering grounds, the isotope signature in that feather would indicate where the duck hatched—the Prairie Pothole Region, the boreal forest, or elsewhere.

Researchers use stable isotope techniques to delineate populations, determine diet, identify habitat preferences, and examine important connections among breeding, wintering, and migration areas. And they are able to get this information without having to follow individual birds from place to place over long periods. This helps conservation planners and habitat managers determine landscape-level conservation practices that will most benefit waterfowl. Because researchers can now track birds throughout their entire life cycle, conservation planners can begin to unravel how events in one season, such as lack of food on spring migration routes, affect events in another season, such as reproductive success on the breeding grounds.