Field Notes
U.S. Fish & Wildlife Service
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Understanding Diving Duck Distribution and Abundance in the Upper Mississippi River and Great Lakes Joint Venture Region
Midwest Region, March 1, 2014
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Many diving duck aerial-survey transects were established by Michigan waterfowl researchers on Lake St. Clair.
Many diving duck aerial-survey transects were established by Michigan waterfowl researchers on Lake St. Clair. - Photo Credit: Greg Soulliere

The Upper Mississippi River and Great Lakes region is important to continental waterfowl populations, especially migrating diving ducks and sea ducks. Abundant high-energy food resources, coupled with warmer weather and the adaptability of some species, has resulted in increasing lengths of stay during migration periods and growing numbers of waterfowl spending the winter. Estimated annual "duck-use days" (number of ducks multiplied by number of days in area) for the Midwest region now total about 800 million for winter and spring periods combined according to the Upper Mississippi River and Great Lakes Region Joint Venture (JV) Waterfowl Habitat Conservation Strategy.

 Toward the eastern side of the Great Lakes region, where the St. Clair River empties into Lake St. Clair, lays one of the world’s largest freshwater deltas, a wetland and open-water system shared by Canada and the United States. Historically, the Lake St. Clair complex and nearby western Lake Erie have hosted peak numbers of 750,000 diving ducks during fall, with canvasbacks, redheads, lesser scaup, and greater scaup being prominent species. Associated with high duck use is a long tradition of diver hunting in U.S. waters of Lake St. Clair, but hunter success declined in the early 2000s while populations of diving ducks using the lake appeared to be increasing, prompting research to better understand the system.

Using historic (1983-2009) and current (2010-12) diving duck aerial survey data, researchers (Michigan DNR and Michigan State University) compared scaup, canvasback, and redhead abundance and distribution on U.S. and Canadian waters of Lake St. Clair. GPS locations were recorded for all diving duck flocks and for human activity on the lake, allowing development of spatial models to investigate the effects of past and current environmental and anthropogenic variables on diving duck distribution.

This effort uncovered a relationship between colonization by exotic Dreissenid (zebra and quagga) mussels, increased water clarity, and human disturbance (e.g., pleasure boating, anglers, and waterfowl hunting via open-water layout boats), but with some species-specific differences. For example, although continental scaup populations declined during the assessment period, fall-staging scaup numbers increased at the study area, likely related to an abundant new food source (Dreissenid mussels) available to the largely carnivorous scaup. In addition, increased water clarity of the lake associated with mussel invasion resulted in expansion of submerged aquatic plants and increased canvasback (largely a vegetarian) use of new and deeper vegetation zones.

Unfortunately, U.S. hunters enjoyed only limited benefits from these lake-wide increases in diving duck populations. High disturbance from boating activity (always in U.S. waters) resulted in diving ducks shifting from U.S. to Canadian locations for a majority of their activity during day-light hours.

Decreased use of U.S. waters by diving ducks in the past 10-15 years was likely a result of system-wide changes on Lake St. Clair initiated by Dreissenid mussels. The entire lake appears to have transitioned to a food-rich system, and consequently, diving ducks no longer tolerate the level of disturbance and hunter-related risk they did historically to exploit available forage. Rather than exclusively using the relatively shallow but highly disturbed U.S. portion of Lake St. Clair, expanded food resources and higher water clarity have allowed diving ducks to 1) feed more efficiently, 2) loaf in secluded, offshore Canadian waters during the day and forage in the U.S. nocturnally, and or 3) simply forgo using U.S. waters entirely because of increased food abundance in the relatively deeper Canadian waters of the lake.

Although food availability undoubtedly plays the primary role in distribution and abundance of migrating waterfowl, researchers in the Great Lakes region found negative correlations between boats counted (disturbance) and abundances of diving ducks. Diving ducks had options at this study location, but obviously disturbance must be an important management consideration at most waterfowl stopover sites. Like other regions important during the non-breeding period, waterfowl conservation planners in the Upper Mississippi River and Great Lakes region assumed food energy was the factor most limiting duck use during migration and winter. Great Lakes diving duck researchers supported by the JV identified considerations and pitfalls of this simple assumption. The Lake St. Clair research team pieced together a much better understanding of the complexity and dynamics of a system critical to non-breeding waterfowl.

Contact Info: Gregory Soulliere, 517-351-4214, Greg_Soulliere@fws.gov
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