Wednesday, February 14, 2018

Greater Scaup: An eBird problem child

[Click on images to see larger versions.
Immature male Greater Scaup, Cape May Pt., Cape May Co., NJ; 7 January 2012. Photograph by Tony Leukering.]

Greater Scaup is of regular occurrence in our two-state region, but is both over- and under-reported, due to the extreme difficulty that many birders -- even skilled ones -- have at identifying scaup.  Leukering has treated this subject in some detail elsewhere (Leukering 2011).  We strongly recommend reading that paper first, but we know you won't, so this essay is meant to point out a few factors in scaup identification that are over-looked or ignored by -- or unknown to -- many birders.

We start with some bulleted cautions:

  • If the scaup that you are ogling is foraging; beware!  Head shape is not a useful differentiating feature of foraging scaup.
  • If the scaup that you are ogling has water drops on its back and/or elsewhere; beware!  That bird has recently been foraging; see previous caution.
  • If the scaup that you are ogling does not have bright yellow eyes; beware!  Dull eye color is a sign of immaturity, and head shape in scaup with juvenile head feathering is not a useful differentiating feature.
  • If the scaup that you are ogling is a male that lacks complete adult-like plumage, particularly after December; beware!  Males lacking complete adult-like plumage after December are probably immatures; see previous caution.
  • If the scaup that you are ogling is brown; beware!  The timing of the molt out of juvenile plumage is quite variable across individuals of both species, such that immature males still with juvenile head feathering can be found very deep into winter.  Additionally, eye color may change well ahead of plumage change, such that even scaup with yellow eyes may still hold juvenile head plumage; see previous caution.
  • If the scaup that you are ogling is brown and large and has a slight peak in front of the eye; thin-but-distinct eye rings; thin, pale post-ocular line; and looks like this; beware!  The bird that you are ogling is a female Redhead.
  • If the scaup that you are ogling has an apparently green head; beware!  The iridescent plumage of male scaup is not, WE REPEAT, NOT, a reliable differentiating feature of scaup -- or of any other similarly plumaged species.  Note the head color of these males: 

               November, California

               January, Florida

               January, Colorado [the best of the lot]

Scaup ID has always been difficult, with, perhaps, the majority of birders not being able to consistently ID them correctly.  Even skilled birders have trouble with this duo, so do not be afraid to use the "Greater/Lesser Scaup" entry in eBird.  In fact, we will make it more plain:  Use the "Greater/Lesser Scaup" option unless you are certain of the ID of the scaup (singular or plural) you are ogling.

Okay, one more caution, and then we'll get to the meat of this essay.  Finally!


  • If the scaup that you have ogled is represented in your photos/eBird checklist by a single picture; beware!  Head shape is changeable and ephemeral, and as with identification features, the more of them you have, the better.  The more photos, the more likely that you will have captured the "true" head shape.

  • One of the problems that birders create for themselves concerning scaup ID is not knowing the difference in sizes of various duck species.  For whatever reason or reasons, many or most birders seem to think that diving ducks are large, particularly relative to dabbling ducks.  However, the reverse is true.  Paying attention to neighboring ducks when ogling a scaup and determining the scaup's comparative size is very helpful.  If that scaup is among other "bay ducks" (genus Aythya), size can be quite helpful, as:

    Canvasback > Redhead > Greater Scaup > Ring-necked Duck ≥ Lesser Scaup.

    If that scaup is among dabbling ducks, then:

    Mallard > Northern Pintail > Gadwall ≥ American Wigeon > Northern Shoveler > 
    Greater Scaup > Lesser Scaup ≥ Cinnamon Teal > Blue-winged Teal > Green-winged Teal

    Combining all of these species results in:

    Mallard > Northern Pintail > Gadwall ≥ American Wigeon > Northern Shoveler > Canvasback > Redhead > Greater Scaup > Ring-necked Duck ≥ Lesser Scaup ≥ Cinnamon Teal ≥ Blue-winged Teal > Green-winged Teal

    Of course, the above comparisons are over-simplifications, as I created them from the "average" size values presented in Sibley (2014) [Yes, actually reading the field guides can prove quite useful in bird ID] and the wing-chord values in Pyle (2008).  Unfortunately, there is variation in size in all species, with males averaging larger than females and, at times, adults being larger (at least, bulkier) than immatures.  So, again, determining your mystery scaup's age and, particularly, sex can be critical to slapping the correct ID on the bird, and, below, we present a great example.

    The recent incredible increases in both the number of birders and in the ease with which information about bird occurrences can be shared has exacerbated the problem of mis-identification of scaup.  Additionally, one of those sharing venues -- eBird -- has particularly exacerbated the problem, as anyone can report bird occurrence to eBird, even when the identifications that result in those bird-occurrence data are incorrect.  Thus, the fact that a single birder incorrectly reports a Greater Scaup from a location can create a situation of circular logic about that occurrence, with many other observers visiting that location and also incorrectly reporting that "Greater Scaup."  These sorts of things then take on a life of their own, as few observers then critically examine the bird in question, because "the bird has been reported by others," so one of these scaup must be the Greater.

    This essay is the direct result of one of those situations. Someone (I know not who, and it does not matter) reported a male Greater Scaup at Belmar Park in Jefferson Co., CO, in January.  Others followed, some reporting a Greater Scaup; still more others followed.  Kathy Mihm Dunning, Scott Somershoe, and Tony Leukering, due to eBird-review duties, had seen a number of photos from the location of the purported Greater Scaup, and were sure that the various reports were in error, as none of the photos embedded in eBird checklists provided definitive proof of ID.  In fact, many photos were obviously of Lesser Scaup; some were less-obviously of Lesser Scaup.

    Kathy and Tony visited Belmar Park on 3 February to attempt to solve the problem.  As can be seen in the resultant checklist, they found ten individual scaup.  The number of Lesser Scaup reported on the other 41 checklists that reported scaup from Belmar Park in January and early February 2018 ranged from one to ten.  Greater Scaup were noted on 14 of those checklists, with all but one checklist reporting a single bird.  Thus, it seems unlikely that the "Greater Scaup" in question was/were not present for their visit.  In fact, some of the photos of the purported Greater Scaup were more-than-good enough for us to determine that we saw the same individual birds.  Unfortunately, those birds were Lesser Scaup.  BUT, there was a very interesting brown scaup.  In fact, it was one of the birds depicted in the single checklist that reported brown Greater Scaup.

    When endeavoring to identify a scaup, as with identifying most birds, determining the bird's age and sex are quite helpful when hoping to arrive at a correct ID.  Conversely, if one is not hoping to arrive at a correct ID, then age and sex don't play any useful part.  The primary reason that ageing scaup is critical for species identification is that the head shape of juvenile scaup, particularly that of Lesser, is somewhat to quite different from that of adults.  Yes, the heads of juvenile Lesser Scaup are often fairly rounded.  Here are some examples of immature Lesser Scaup in fall:

    November, El Salvador

    September, Idaho

    September, Idaho [we particularly like the great variety of head shapes depicted in this photo]

    October, Ontario

    Of the Lesser Scaup at Belmar Park on 3 February, there was just a single male wearing complete (or nearly so) adult-like plumage; it is depicted in Figs. 1-2. All other male scaup present were obvious immatures (such as the second bird in Figs. 1-2).


    Figures 1 and 2. Adult male (right) and immature male Lesser Scaup. Note the peaked crowns of both birds, but that the immature's crown is less-peaked. Also note the immature's mix of juvenile and adult-like plumage. Belmar Park, Jefferson Co., CO; 3 February 2018. Photographs by Tony Leukering.

    The only scaup present that caused a slight increase in heartbeat rate was the bird presented in Figs. 3-6 and which provides the aforementioned great example of the usefulness of size comparison when identifying ducks.

    Figure 3. The interesting brown scaup. Note the disheveled plumage on the crown that makes the bird look like it's having a bad-hair day; that plumage is almost certainly juvenile crown plumage, and worn juvenile crown plumage, at that. Also note the handful of grayish feathers present on the sides, which present as whitish streaks. Also note the oddly orange color to the plumage encircling the bill. We do not know what that color means, but it makes for a distinctive scaup. The brown eyes indicate that this bird is an immature. The bits of gray side plumage indicate that this is a male, not, as one might think, a female. Note that it appears quite a bit smaller than the male Northern Shoveler behind it. Finally, note that that male Northern Shoveler's head is purply-blue, not green. Again, the color of iridescent plumage is highly unreliable as an identification feature. Belmar Park, Jefferson Co., CO; 3 February 2018. Photograph by Kathy Mihm Dunning.


    Figure 4. The interesting brown scaup. Note the bird's apparently blocky head, non-peaked crown, and steep forehead. Part of that appearance is due to ephemeral posture, part due to retained juvenile head plumage. Since by this time that juvenal head plumage has been adorning the bird for, perhaps, 7-8 months, it is getting quite worn. That means that the feathers are becoming shorter, which may account for a few of the apparent Greater-like head features presented in this photo. This photo is also highly relevant to the above caution about using a single photo to describe your scaup. Belmar Park, Jefferson Co., CO; 3 February 2018. Photograph by Kathy Mihm Dunning.


    Figure 5. The interesting brown scaup. Note the bird's relatively narrow head and shallow angle created by jowls that do not bulge much (compare with birds on back cover comparison in this essay). Belmar Park, Jefferson Co., CO; 3 February 2018. Photograph by Kathy Mihm Dunning.



    Figure 6. The interesting brown scaup. Note that the scaup looks noticeably smaller than even a female Northern Shoveler. Belmar Park, Jefferson Co., CO; 3 February 2018. Photograph by Kathy Mihm Dunning.

    If you've slogged all the way through the essay: Thanks!  If you've skipped ahead, the solution set to the murder is:  Colonel Mustard, in the kitchen, with the wrench.

    Literature Cited

    Leukering, T. 2011. Greater and Lesser Scaup: Beyond crown shape. Colorado Birds 45:75-78.

    Pyle, P. 2008. Identification Guide to North American Birds, part II. Slate Creek Press, Bolinas, CA.

    Sibley, D. A. 2014. The Sibley Guide to Birds, 2nd ed. Alfred A. Knopf, New York.


    Tony Leukering, Steve Mlodinow, Kathy Mihm Dunning, and Scott Somershoe (half of the Colorado eBird review team)


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