I’ve added this page to provide an explanation as to how we were able to conclusively identify the Western Sandpiper at Morningside Park. Peeps in general are often confusing with age, molt, basic, transitional and alternate plumages all coming into play. As soon as I saw the sandpiper, I knew it was something different than the peeps I’d been seeing so far this season. The bill was too long and droopy for a Semipalmated Sandpiper and the bird was in adult transitional plumage, very pale, had black legs with noticeable orange/rufous bases to the scapulars which of course ruled out Least Sandpiper. The bird was also in the company of a Least and Semipalmated Sandpiper which gave a clear indication that the bird was just slightly larger than the Semipalmated Sandpiper. With two peeps ruled out, now we had to determine whether or not it was a Western Sandpiper or White-rumped Sandpiper. I had the advantage here because I was able to view the bird in flight several times, seeing it had a brown rump. Unfortunately, I was unable to get a photo of the bird in flight. That meant that I had to prove its identity with other characteristics. White-rumped and Western Sandpipers are very similar, and it can be difficult to tell them apart, especially when only one species is present. The White-rumped is a full inch larger than the Western and its wings are so much longer that they project a half an inch or more beyond the tail tip. (note that the primaries don’t project beyond the end of the tail in photo below) This extension almost always results in the tips being crossed, forming a wedge.
Now to our bird. The bird was just larger than the Semipalmated Sandpiper. Close inspection quickly revealed that there was no primary projection beyond the tail tip. I already knew it had a brown rump. The bill was the next determining factor. The bill was long and droopy, by not extensively so. This meant that if it was a Western Sandpiper, being it was an adult, it was a male bird. Females have extensively long bills and are pretty much unmistakable. Superficially however, the bill still resembled a White-rumped Sandpiper. This is where taking extensive photos (I took 140 photos of this bird) if at all possible, becomes crucial. A White-rumped Sandpiper’s bill shows a distinct “< ” at the base of the bill, whereas the Western’s bill is basically “l” in other words, straight up and down. The other diagnostic feature of the bill is that the White-rumped has a distinct orange tinge to orange base of the lower mandible. The Western’s bill is dark black. You will note both the straight edge to the base and the dark black color in the shot below.
Another distinctive feature of a Western Sandpiper is the orange/rufous base to the scapulars. This is dependent on the bird being in either alternate or transitional plumage. A basic plumage bird does not have them. Though hard to get in a photo, you can easily see them in the shot above. The bird still retained orange/red feathers in its face and on its crown further ruling out White-rumped since they are very gray at this time of year. They may show a little rusty red in dark gray feathers in breeding plumage, but that wasn’t what was being seen with this bird.
In summary, we had a peep slightly larger than a Semipalmated Sandpiper with orange/rufous based scapulars, short wings that did not project beyond the tail, a long droopy bill that was dark black with a straight edge at the base of the bill. The bird was in a progressed molt with many back feathers already having molted into the pale gray winter plumage (Western Sandpiper molts during migration). Conclusion: Adult male Western Sandpiper!
I hope this may be of help to someone trying to make an identification between these two birds. I have to admit that my situation at Morningside is unique in that I practically have the birds sitting in my lap, enabling me to take many close-up photographs. The more photos the better!
PS. I’d like to thank Lance Verderame, Zach Schwartz-Weinstein and Shai Mitra for their help with the identification!
Bashakill Birder 