birds frequently congregate in large numbers over mussel beds or other areas 

 supplying rich food resources (Cramp et al. 1977). 



Winter and Offshore During the winter Greater Scaup prefer salt and brack- 

 ish bays and estuaries, as well as large areas of open marine and nearby fresh 

 water (Palmer 1976b). Habitats used by non-breeding birds in the Old World are 

 usually marine and may be tidal and exposed to severe weather. These habitats 

 include partially landlocked, low saline seas, such as the Baltic. Brackish and 

 fresh waters are used less extensively, and rivers are uncommonly frequented 

 (Cramp et al. 1977). Scaup wintering off the coast of Connecticut did not feed 

 on mudflats but were seen feeding in breaking surf (Cronan 1957 in Palmer 1976b). 



FOOD AND FEEDING BEHAVIOR 



Greater Scaup feed primarily by diving using only the feet for propulsion, 

 but they occasionally tip-up and dabble as well. They feed throughout the day, 

 often in large flocks, and may also feed at night, particularly when disturbed 

 (Cramp et al. 1977). One study conducted off Connecticut (Cronan 1957 _in Pal- 

 mer 1976b) reported that these birds made dives of up to to 23 ft (7 m) but 

 that most dives were much more shallow. These dives averaged 20.4 sec, with a 

 range of 9-33 sec. 



Summaries by Palmer (1976b) and Cramp et al. (1977) provide detailed ac- 

 counts of the foods eaten in the New and Old Worlds, respectively; these should 

 be consulted for more extensive listings of foods eaten by Greater Scaups. Our 

 remarks below are largely condensed from these two sources. 



Food may be either vegetable or animal in origin and may vary considerably 

 from area to area and from season to season. It was nearly equally divided 

 (46.5% - animal) in one study of 752 stomachs from North America. Pondweeds 

 ( Potamogeton , Ruppia , Phyllospadix , etc.) were the principal plants eaten and 

 constituted 18.9% of the diet. Bivalve molluscs (23.2%), snails (15.9%), aquat- 

 ic insects (7.2%), and crustaceans (6.8%) were the principal animal foods con- 

 sumed. 



In some areas (e.g., along coastal lakes and streams in British Columbia), 

 fish and fish eggs may be important items of diet. In other areas, muskgrass 

 ( Chara ) may form the bulk of the food. A number of studies indicate that bi- 

 valve molluscs constitute the major food of birds wintering on saltwater. 



Little quantitative information on the food habits of Greater Scaup in the 

 southeastern United States is available. We summarize this material by state 

 below. 



Florida Stieglitz (1967) reported the foods eaten by four Greater 

 Scaup wintering near Cabbage Island in Apalachee Bay on the Florida Gulf coast. 

 These birds had eaten almost solely gastropods (85.2% by volume) and mud crabs 

 ( Rithropanopeus sp. - 13.8%). Molluscs consumed to the greatest extent were 

 greedy dove-shell ( Anachis avara - 35.4%), variable nassa ( Nassarius ambiguus - 

 26.3%), and Atlantic modulus ( Modulus modulus - 20.0%). The only plant food 

 found was shoalgrass ( Diplanthera wrightii - 1.0%). 



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