The Lesser Scaup (Aythya affinis) is considered the most abundant diving duck in North America. However, it has been identified as a focal species of management concern due to serious declines in the combined breeding population of Greater and Lesser Scaup in North America. The combined population has fallen from an estimated 5.7 - >7 million scaup in the 1970s to a record low of 3.25 million in 2006. Population estimates for Lesser Scaup alone are difficult to determine because they cannot be distinguished from Greater Scaup (Aythya marila) during surveys. Lesser Scaup are estimated to constitute about 90% of combined continental population of scaup, based on their known distribution in the western boreal forests of Canada and Alaska, and the northern prairies; hence, concerns about the declining scaup population have largely focused on Lesser Scaup. What may have contributed to the scaup decline is uncertain, but major concerns include declining breeding habitat due to climate change and human development, changes in food resources and contaminants on migration and wintering areas, invasive species, human disturbances, and degraded habitat in important migration and wintering areas. Warming trends in the northern boreal forest may be causing long-term loss of wetland habitat important to scaup for nesting and brood-rearing. Degraded wetlands, particularly in the upper Midwest, provide poorer quality foods to scaup during spring and fall migration than they did historically. Exotic zebra and quagga mussels that have invaded important migration and wintering habitat of the Great Lakes and Upper Mississippi River system concentrate pollutants and have largely replaced native mollusks as scaup foods. An internal parasite introduced into the Upper Mississippi River system has resulted in repeated die-offs during migration. Development pressures along the Pacific, Atlantic, and Gulf coasts have degraded freshwater and estuarine wetlands important to wintering scaup. Habitat losses, changes in distribution, and declining numbers also have reduced opportunities for diving duck hunters in many areas.

Date: July 2009

Sources:
Afton, A. D., and M. G. Anderson. 2001. Declining scaup populations: a retrospective analysis of long-term population and harvest survey data. Journal of Wildlife Management 65:781-796.

Austin, J.E ., A. D. Afton, M. G. Anderson, R. G. Clark, C. M. Custer, J. S. Lawrence, J. B. Pollard, and J. K. Ringelman. 2000. Declining scaup populations: issues, hypotheses, and research needs. Wildl. Soc. Bull. 28:254-263.

Austin, J. E., C. M. Custer, and A. D. Afton. 1998. Lesser Scaup (Aythya affinis) . The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology. Retrieved July 2009 from http://bna.birds.cornell.edu/bna/species/338.

Badzinski, S. S., and S. A. Petrie. 2006. Diets of Lesser and Greater Scaup during autumn and spring on the lower Great Lakes. Wildlife Society Bulletin 34:664-674.

Bellrose, F. C. 1980. Ducks, geese, and swans of North America. 3rd ed. Stackpole Books, Harrisburg, PA. 540pp.

U.S. Fish and Wildlife Service. 2009. Waterfowl population status, 2009. U.S. Department of the Interior, Washington, D.C. USA.