Dowitchers: Oh, For the Love of Birding!

Figure 1

Whenever I go to Merritt Island, I cross the Max Brewer Bridge and stop just after the bridge in the little parking lot on the north side of the road.  It doesn't look like much, but I frequently see Dunlins, Sanderlings, Ruddy Turnstones, Dowitchers and other shorebirds, as well as Gulls, Black Skimmers, Ospreys and a few herons.  A couple weeks ago, some Dowitchers graced us with their presence.   There are two species of Dowitcher, the Long-Billed and the Short-Billed, and it's notoriously difficult to distinguish between them, especially in their winter (basic) plumage.  On average, the Long-Billed (LB) has a longer bill than a Short-Billed (SB), but there is variation in the sizes of the bills in both species.  Female bills tend to be longer than male bills in both. This means that male LBs have bills that significantly overlap in size with female SBs.  Since their bill sizes overlap in length so much, they are not a very reliable indicator of the species.  So I did what I suspect most bird photographers do; I studied the birds, took a bunch of pictures of many of them, and then studied the photos at home.  A gallery with more photos of these birds can be seen here.

Figure 2

I try not to spend too much time in the field consulting field guides. I do use them,  but too many times I've been excited about identifying a bird, and while consulting the field guide, the bird flew away, leaving me with nothing to go on.  So now I spend my time studying the birds, photographing them in as many positions as possible.  It's particularly helpful to photograph a full profile.  This is the best way to see the bird's bill shape and length in relation to its head, the length of the wings with respect to the tail, and many other features.  These helpful diagnostic clues can be obscured when photographs are taken at an angle.  Compare figure 3 with figures 4 and 5 (these are 3 different birds).

Figure 3

Figure 4

Figure 5

With these photographs, I consulted my field guides and Stokes excellent Beginner's Guide to Shorebirds, but I was still undecided.  So I searched the internet. I found a couple articles about how to distinguish between them, one by Cin-Ty Lee and Andrew Birch (pdf version) and the other by John Takekawa and Nils Warnock (this is a free summary of the article).  Comparing my photos to these articles led me to conclude several things:

1. In figures 1 and 3 (same bird), the bill length about twice the length of the head; this suggests they may be LBs. In figure 1, it looks to be even more than twice the length of the head.
2. In figures 1,2,3,5, the primaries (wing feathers that come from the birds "hand") in these birds do not extend to the end of the tail, also suggesting that they may be LBs.  Some, but not all SBs have primaries that extend 2-3mm beyond the tail.  And feathers wear, so this is not a perfect guide either.
3. In figure 5, the tail appears to have thicker black banding than white, suggesting LB, but figures 1 and 3 do not appear this way, suggesting SB.  There is variation and overlapping in this field mark, so this again is not decisive.
4. In figure 3, the best profile shot I have, the "loral angle" appears to be very shallow. The loral angle is the angle created by drawing a straight line along the bill and another line from the eye intersecting with the bill at the base. See this photo to see a visual portrayal of the loral angle of fig. 3; Jay W (in the comments below) drew the angle on the image. The LB has a shallower loral angle (averaging about 15-16 degrees) than a SB (averaging about 21 degrees).  This is a fancy way of saying that the eye of the SB is higher on the head than with a LB.  
5. In figure 5, the bill appears to droop slightly downward, which is more likely in SBs.

After looking at all this, I was leaning to Long-Billed, but I was still a little undecided.  So I swallowed my pride and asked for help.  I submitted a few photographs to the Florida "Birdbrain" listserve.  The responses were extremely helpful, though some thought these were Long-Billed and some Short-Billed.  Here are some observations they made that went beyond what I had observed.

1. Since I found these birds by salt water, many believed these are more likely to be SBs.
2. In these photos, the birds appear to have flatter backs, like SBs.  LBs tend to have a hunch-backed look, like the bird had swallowed a grapefruit.  This is particularly the case when the birds are probing for food.
3. Another measured the loral angle of the bird figure 3 to be about 13 degrees (I got the same measurement for figure 1, but it's not a pure profile view).   While there is significant variation in the loral angle of these birds, a 13 degree loral angle on a SB would be very unusual.
4. LBs should have a darker chest without streaks or spots, giving a stronger contrast between chest and belly than SBs.  To me, this leads me to think that figures 1 and 3 are more likely a LB.

So with this added help from the listserve, here's what I now think.  While none of the above are definitive individually, collectively they lead me to think that the bird in figures 1 and 3 (they're the same individual) is a Long-Billed Dowitcher.  I'm still undecided with the others; it may be that I photographed a mixed flock of LBs and SBs.  I'd love to hear other thoughts on these.  If you have any insights, please let me know in the comments below.

This is what we do "for the love of birding," and this experience has reminded me of three important points: 1) birding can be both fun and hard work, 2) birding is better done with the help of others and 3) it's okay to say "I don't know."

***

UPDATE 11/30/2011 - I've gotten some great feedback from Cameron Cox through the FL Birdbrain listserve.  The bird in figures 1 and 3 has a long, straight bill with consistent thickness throughout the length of the bill and a more pointed tip.  It also has a dark chest contrasting with a white belly.  It's a female Long-Billed Dowitcher.

Figures 2 and 4 have birds with grey spotting on the the breast that cause a more gradual change form grey to white on the belly.  Their bills are thicker at the base and thin toward the tip with a slight downward droop.  These are Short-Billed Dowitchers.

Figure 5 is a little more tricky. The bill is probably too short for a female Long-Billed, but within the range of a male, and the barring on the tail suggests it's also a Long-Billed Dowitcher.  It has a thicker bill at the base (more like a Short-Billed), but a more pointed tip (more like a Long-Billed). So he's tentatively calling it a male Long-Billed Dowitcher.