Avocet, and Knot Your Basic Dunlin - 05 Jun 2014
I took a late-afternoon ride to check shorebirds in Cell 3 at Pointe Mouillee SGA. I parked at Roberts Rd and rode the bike over to Cell 3. Interestingly, I found a patch of mudflat in the NW corner of Cell 1 that could be productive for shorebirds later this summer. It's about an acre in size with water deep enough to support a couple dozen Mallard and several Blue-winged and Green-winged Teal.
As I arrived at the SW corner of Cell 3 I took a moment to digiscope an Eastern Kingbird along the shoreline.
As I looked out over the large mudflat I found only a few Caspian Terns at the tip of the peninsula and a pair of peeps along the waterline. One was a Semipalmated Sandpiper while the other looked like a Dunlin, but it appeared to be a bird in complete basic plumage. This had me concerned that I might also be looking at a Curlew Sandpiper(?) as I didn't expect to see a Dunlin in nonbreeding plumage this late in the spring. A scope view of the NW corner of the cell showed numerous Dunlin, and all of those birds were in alternate plumage, so this bird was going to need some extra attention.
The mudflat was dry enough to support my weight so I hiked out so that I might get close enough to get some pics for verification. As I walked out toward the tip I noticed the American Avocet that Kim Diel Leedom reported earlier in the day on Facebook. So I paused to digiscope the bird before it flew off to the NW corner of the cell.
The Dunlin was foraging in deep water all by itself. The uniform brown bird with the long, decurved black bill showed evidence of a white supercilium that is distinct in the much rarer Curlew Sandpiper. I only managed a few long distance photos before it flushed and headed toward the NW shoreline. I was lucky enough to grab a couple of flight shots that gave me a view of its rump, as it would be important for verifying ID. While walking back to the dike I could a Yellow-headed Blackbird calling from the Humphries Unit.
I caught up with the Dunlin and got a few more digiscoped images before it flew back toward the SW corner.
Meanwhile, I scanned the NW mudflats and found breeding-plumaged Dunlin, Least and Semipalmated Sandpipers, couple of Pectoral Sandpipers and a pair of Lesser Yellowlegs. Along the waterline about 100' out I spotted a single Red Knot. I decided to digiscope it for record.
As I photographed the Red Knot the avocet wandered into view, giving me the opportunity to get both birds in the same scope view! I then spent the next 20 minutes digiscoping the avocet as it foraged in my direction. I kept thinking that I needed to spend more time verifying the identification of the basic-plumaged sandpiper, but it's not everyday that an American Avocet is posing 30' away during the "Golden Hour", so I stayed a while longer.
I finally headed back to the SW corner for one last look at the basic-plumaged shorebird.
When I finally got home I consulted my shorebird guides to compare Dunlin and Curlew Sandpiper traits. O'Brien, et. al. (2006) lists the Curlew Sandpiper (Calidris ferruginea) and Dunlin (Calidris alpina) as overlapping in length and weight, so size-wise, they are very similar. Dunlin subspecies C. a. hudsonia are known to show streaking along the flanks that are visible in eclipse (non-breeding) plumage (Paulson, 2005). Things to look for in a Curlew Sanpiper in basic plumage include: distinct white supercillium, white belly w/o spotting or marks on flanks, 'slender' look and 'taller' appearance with slightly thinner bill relative to Dunlin, and 'white rump' that is larger in coverage than a White-rumped Sandpiper. Wing projection also extends beyond the tail, whereas Dunlin wing projection is just short of the tail.
Things to look for in a basic plumaged Dunlin include: smoky gray / brown plain plumage with distinct hood appearance, lack of distinct supercillium, chevrons or spots along flanks, bulkier appearance, and dark rump w/ little white. From the images above you can see wing projection just short of the tail.
Late summer / early fall is typically the time when confusion between Dunlin and Curlew Sandpipers can occur. I found a couple of good articles that summarizes their differences and what to look for when trying to identify 'mystery' birds: http://www.dublinbirding.ie/pages/features/Curlew%20Sand%20ID/getting_to_grips_with_curlew_san.htm and http://www.oceanwanderers.com/BSmallSHorebird.html. Both are worth looking at, as well as the slew of photos that are available online. Just Google 'basic plumage Curlew Sandpiper'.
In the end I think there's no confusing this bird as anything but your basic Dunlin. But I'm glad I spent some time chasing it and learning a bit more about what to look for when that Curlew Sandpiper does show up at Pt. Mouillee. After all, we're overdue for another one...
Hayman, P., Marchant, J., and Prater, T., Shorebirds, An Identification Guide, 1986, Houghton Mifflin Co., Boston.
O'Brien, M., Crossley, R., and Karlson, K., The Shorebird Guide, 2006, Houghton Mifflin Co., Boston, New York.
Paulson, D., Shorebirds of North America, The Photographic Guide, 2005, Princeton University Press, Princeton and Oxford.