Lesser scaup breed and raise their young may be tied to some specific ecological conditions—such as abundance of key food items—which shifted winterwards due to global warming, without the ducks being able to adapt. In this regard, it is alternatively or additionally possible that greater scaup, which may be increasing in numbers, is putting the lesser scaup under increasingly severe competition. However, it seems that greater scaup eats larger food items on average, and the species are sympatric in part of their range and presumably have been for millennium without any problems due to competition. The experience of the past as well
Greater scaup greater tends to be more rounded, and the white wing stripe is more extensive. The greater scaup has a circumpolar distribution, breeding within the Arctic Circle both in the Old World (the Palearctic) and in North America (the Nearctic). It spends the summer months in Alaska, Siberia, and the northern parts of Europe. It is also found in Asia and is present in the Aleutian Islands year round. The summer habitat is marshy lowland tundra and islands in fresh water lakes. In the fall, greater scaup populations start their migration south for the winter. They winter along the Pacific and