Scientists at Mississippi State are among those who want to know why populations of lesser scaup—or, as they're commonly known, bluebills—continued to decline while most species of North American waterfowl experienced dramatic increases during the 1990s.
Recent joint studies by faculty in the university's Forest and Wildlife Research Center and College of Veterinary Medicine, along with colleagues at Louisiana State University, are homing in on some possible causes.
According to one theory, food and habitat conditions during spring—versus those in the fall and winter seasons—may be contributing to the decline. The lesser scaup migrates and winters primarily in the Mississippi Flyway, named after the Mississippi River which the birds follow during fall and spring migration. (By contrast, the greater scaup winters largely in the Atlantic Flyway along the Atlantic Ocean.)
"Bluebills remain the most abundant diving duck in North America,” said Richard M. Kaminski, waterfowl/wetland ecologist and professor in MSU's wildlife and fisheries department. "Since the late 1970s, however, their populations have been ‘diving.'”
Finding reasons for the decline is important to the 20,000 Mississippi waterfowl hunters who annually harvest more than 400,000 ducks. It's also a compelling economic issue in a state where duck hunters spend nearly $30 million annually.
Joining the combined MSU effort are scientists at LSU and the Louisiana Cooperative Fish and Wildlife Research Unit. During three successive fall and winter seasons ending in 2001, MSU wildlife and fisheries graduate student Josh Vest of West Point collected bluebills throughout the Mississippi Flyway.
Vest's work, compiling information on the birds' body weights and internal parasite levels, was funded by the Delta Waterfowl Foundation through the Delta Waterfowl and Wetlands Research Station, Ducks Unlimited's Institute for Wetland and Waterfowl Research, and the U.S. Fish and Wildlife Service.
"Scaup collected from Mississippi catfish ponds weighed about 60 grams more, on average, than those harvested from traditional wintering habitats in Louisiana,” Kaminski said. "This suggests that catfish ponds may be a healthy habitat for them.”
The research also determined that body weights of collected bluebills were greater than or similar to estimates from birds collected in the 1980s before the precipitous decline. "The finding suggests that in the Mississippi Flyway, current food and habitat conditions during fall and winter may not be affecting scaup populations,” Kaminski added.
Scientists also determined that, while parasite levels generally increased with body weight, current parasite burdens were similar to those in bluebills collected during the 1970s—again before the major decline in populations.
Linda Pote, MSU professor of veterinary medicine, said, "It appears that total parasite burdens have not increased in recent decades and may not be influencing the scaup population decline.” She said few factors were found in the Mississippi Flyway to impact bluebill populations for the fall-winter migration.
By contrast, an ongoing LSU study has uncovered evidence that food resources and body conditions of bluebills along spring migration routes in the Mississippi Flyway and on the breeding grounds are significantly less than 20 years ago.
"The companion MSU-LSU studies are helping to piece together the puzzle of declining scaup,” Kaminski said. "While we have not found the answer, we now know where to direct future research to sustain this important diving duck species.”