Waterfowl researchers have used isotope analysis to answer several interesting questions. For example, we know little about some species of ducks because their habitat is so remote. Sea ducks, for instance, remain in northern areas throughout most of their life cycle. King eiders winter on the northeast and northwest coasts and nest in the high Arctic. Their numbers are declining on both coasts, but wintering birds likely encounter different environmental influences on each coast. Biologists wanted to know whether king eiders wintering on different coasts mixed on the breeding grounds, as well as whether specific wintering areas were affecting reproduction differently. Using band recoveries to delineate these wintering populations was not possible because few king eiders have been banded. On the breeding grounds, researchers wanted to be able to determine if an individual hen king eider wintered on the east or west coast. They collected hens’ head feathers, which are grown on wintering areas, and examined them for stable isotope differences. The results allowed biologists to delineate eastern and western wintering populations on the breeding grounds.
Another waterfowl mystery has been whether the locations selected by hens in winter and spring have an effect on their condition when they arrive on the breeding grounds. Hens that arrive on the breeding grounds with good fat reserves are more likely to nest and successfully raise ducklings. Using isotope analysis, waterfowl managers can identify wintering and migration areas where hens fail to build adequate fat reserves and can then focus conservation efforts on improving habitat conditions and food availability in those areas.
One hypothesis for the decline in the northern pintail population is that the arrival condition of breeding hens may be limiting their reproductive success. DU researchers studied pintail hens arriving in Alaska during spring by analyzing breast feathers (grown in winter) and blood (which reveals the bird’s activities over a small window of time during spring migration). The results showed that pintails that wintered or staged during spring in coastal habitats with more agriculture nearby arrived with less fat than those wintering and staging in freshwater habitats with less agriculture nearby. As a result, researchers might focus efforts on the Gulf Coast and in western Mexico and the Pacific Northwest to determine if food resources are inadequate in these vital coastal areas.
Advances in stable isotope analysis have resulted in large gains in our understanding of waterfowl and other wildlife, but this fascinating field of science has also been used to track sources of pollution and oil spills, trace contaminants in food, identify the origin of illegal drugs, and even determine the diet of Neanderthals.
Dr. Tina Yerkes is director of conservation planning at DU’s Great Lakes/Atlantic Regional Office in Ann Arbor, Michigan.