Two varieties of scaups frequent east-central Florida. Telling them apart can be a little challenging, especially if they are not seen together, but there are a couple of tips that might help.
Greater Scaups generally have flatter or rounder heads, compared to Lesser Scaups. Lesser Scaups often have a slight crest or point at the top of the head, behind the eye. Head color is sometimes mentioned as a way to tell them apart, and in the photos below you can certainly see how the Lesser Scaup has a redder head. My experience in the field, however, shows that sometimes the head colors are almost indistinguishable.
When seen from the front, Greater Scaups have a wider head bill and nail (the spot at the tip of the bill). The Lesser Scaups’ bills and nails tend to look “squished” sideways. The photo below and to the right isn’t exactly head-on, but you can see how the nail is almost completely round, while the nail on the Greater Scaup (on the left) is a bit wider than it is tall. There is certainly overlap, and viewing angle can complicate things, but at least it is another ID tool that might help with a positive identification.
Remember, not all birds can be positively identified every time. I have ambiguous bird sightings almost every time I’m out (birding or just doing errands). For example, more subtle point between these two species is the amount of white showing on the sides when these ducks are on the water. Normally, more white shows on the Greater Scaup, while less is evident on the Lesser Scaup. In the photos above, you can see more white on the Lesser Scaup. Trying to figure out what’s what is sometimes its own reward. The joy of birding is in the journey.