Birders often have to look for structural differences among birds to clinch the identification when plumages give little evidence. I was reminded of this earlier this week when I found some scaup on the lake at Colonel Francis Beatty Park, located just outside Interstate 485 in Matthews.
Scaup are diving ducks that winter in our area. There are two species: the lesser scaup and greater scaup. Both species are extremely similar in plumage. Subtle differences can be seen in males in plumage, bill size and head color when in bright sunlight. Such a setting can aid a birder in making the right call, but there is a range of variability.
The fact that the two birds I saw were females in almost identical plumage narrowed down the field marks that I could use to tell which species I was dealing with. The most reliable way to tell the scaups apart is head shape.
Lesser scaup have a more vertically elongated head that often gives a peaked appearance. Greater scaup have a more rounded head. These differences can be readily seen in typical individuals. And when the two species are seen together, identification can be fairly easy.
One female was clearly a lesser scaup, the most common species encountered in Mecklenburg County. The other bird had a more rounded head, though, and after a while I was pretty sure I was looking at a greater scaup. There are lots of local records for greater scaup, too, but they are very uncommon at best. I can go a few years without seeing one here.
But head shape can vary too. Depending on the demeanor of the bird (relaxed vs. alert, for example) or if the head is wet with feathers slicked back (it was), the identification can be easy or challenging.
I wanted to add greater scaup to my County Year List but recognized this wish may have biased my call. I asked some other local birders to check out these birds. Fortunately, each felt the same way I did. (The greater scaup is the bottom photo.)
Taylor Piephoff is a local naturalist with an interest in the birds and wildlife of the southern Piedmont: PiephoffT@aol.com.
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