As early morning dawns, snow flakes and a strong north wind pound relentlessly against bobbing decoys and duck hunters hunkered down in a makeshift blind along the Mississippi River. Flocks of lesser scaup -- bluebills -- whiz by seemingly at speeds faster than an Indy race car. A few shots echo as the bills fly on unscathed. Indeed, many duck hunters can associate with my memories and those of my twin brother, Matt, of this treasured hunting experience.
However, memories such as ours might decrease, as the North American scaup population continues a 30-year decline. In 2007, the United States Fish and Wildlife Service estimated the breeding bluebill population at 3.5 million, down from 7.5 million in the 1970s. This significant decline has perplexed waterfowl biologists for more than a decade, while other duck populations have increased.
Biologists pose numerous hypotheses for the bluebill population decline. One hypothesis purports that contaminants -- specifically chromium and selenium -- are "bioaccumulating" in female bluebills and impacting their survival, reproduction and, ultimately, population growth. Because Matt and I love scaup hunting with our dad, Dale, we remain intrigued by the population decline.
While students at Winona Senior High School, we read the latest research on contaminants in migrating and breeding bluebills and wondered how these contaminants got into scaup habitat. Growing up along the Mississippi River in Winona, we learned about water quality testing for these contaminants and proposed for our high school science projects that bluebills might be eating contaminated invertebrates.
To test our hypothesis, we collected thousands of invertebrates from wetlands and waterways in Iowa, Minnesota, North Dakota, South Dakota and Wisconsin. These included invertebrates commonly consumed by scaup such as scuds, midge larvae, fingernail clams, snails and exotic zebra mussels.
Our results were surprising. Zebra mussels, known for their water-filtering ability, contained low concentrations of chromium and selenium, while amphipods contained the greatest concentrations of chromium. We also found fingernail clams to contain alarming levels of selenium, exceeding the environmental quality threshold for these invertebrates. As we predicted, wetlands surrounded by more developed land harbored invertebrates with increased concentrations of chromium and selenium.
So what does this mean for bluebills? We don't understand the full consequences of contaminants yet, hence research must continue. For example, we need a better understanding of the distribution of wetlands with environmental contaminants, when bluebills are consuming contaminated invertebrates and whether this foraging is impacting scaup survival and reproduction. Unfortunately, we cannot eliminate all contaminant concentrations in our environment, but habitat conservation practices of the Farm Bill and by public and private organizations (Minnesota DNR and Ducks Unlimited, for example) will help restore wetlands and hopefully scaup populations.
Indeed, improved habitat -- and greater availability of invertebrate foods -- can help "heal" duck and other wildlife populations and stimulate population growth. Increased populations of scaup and hunting opportunities will produce steadfast memories of scaup skydiving toward decoys for us and other dedicated waterfowlers and conservationists for years to come.