Comparison of Greater and Lesser Scaup
Separating Greater from Lesser Scaup is a real challenge. Some individual birds in certain postures can be relatively easy. Other individuals can be a greater challenge. Head shape is considered the key to separating the two species, but changes based on the activity, such as resting or diving (the wet head). The color of the head is not generally a good field mark as it is variable based on lighting conditions. Take comfort in the fact that correctly picking a Greater Scaup out from a group of Lesser Scaup might be next to impossible. It takes a lot of experience and skill to correctly ID the less common Greater Scaup.
Lesser Scaup are more wide spread and far more common in many parts of the country.