Thanks to Rob for inviting me to be a guest blogger just as we start one of my favorite times of the year. Waterfowl migration is in full swing so let’s try to answer that age old question: “Is that a Lesser or a Greater Scaup?”
Over the years I have repeatedly heard that head color is a great way to separate the male scaup species; blue for Lesser Scaup (LESC) and green for Greater Scaup (GRSC). There are several problems with this method. First, this does nothing to help us with the females. Second, in poor lighting such as back lighting or heavy overcast, the head will be nearly colorless appearing black even at relatively close range. Lastly, when viewing in good light the green head for male GRSC is quite reliable, however more than 50% of my LESC images show a bird with a green head.
The following images and captions will illustrate a number of other key field marks to consider. Comparison photos will show the Lesser Scaup on left.
|Another aspect of head shape to consider is the large jowls or “cheeky” appearance of|
the GRSC. The LESC has a much finer build. This trait is not as easy to see when
a bird is in perfect profile as in the first head comparison image.
Sometimes with the above clues scaup ID can be quite straight forward. Other times we need to rely on the preponderance of the evidence. While weighing the evidence it is good to keep a few additional things in mind.
|First, head shape is difficult to judge in flight. This is a LESC showing a green, roundish head.|
|Second, preening and scratching scaup sometimes roll over on their sides which at a|
distance will flash what appears to be a very white flank. What may look like a good
indicator for GRSC may in fact be the very white belly of a LESC.
Even with quality optics and a great understanding of scaup identification we are sometimes left with no choice but to label a bird as scaup species and there is nothing wrong with that!