Calidris pusilla
Order Charadriiformes
Family Scolopacidae
Subfamily Arenariinae
Other names: Peep
Adult in spring.— Under parts brownish-gray, mixed with black; breast spotted with black; rest of lower parts white; legs black.
Adult in fall.— Upper parts plain grayish; breast unspotted.
Immature.— Upper parts gray, mixed with black and a little reddish-brown; under parts white, a dusky wash across the breast.
The Semipalmated Sandpiper is a common migrant along the sea-coast in May, July, August, and September. It not infrequently occurs on the shores of inland lakes, and is an abundant fall migrant in the Hudson Valley. Gunners call this species and the Least Sandpiper, with which it often associates, “Peep.”
The Least prefer the sloughs or muddy pools in the marshes; the Semipalmated frequent the beaches, but both species may occur in either place. Both species associate with Sanderling on the beach, and with White-rumped Sandpipers and Ring-necks [Semipalmated Plover] both on the beach and in the marsh. When with Ring-necks, the difference in behavior is amusing: the Ring-necks scatter about and stand in thoughtful attitudes; the Peep feed with nervous haste, head down, and bill in the sand.
When startled, the Semipalmated Sandpipers utter a little rough peep, and fly in compact bands further up the beach; they have also a very pretty whinnying note, and in May occasionally utter the love-song, a series of sweet notes delivered in the air. When the Least and Semipalmated Sandpipers occur side by side, it is evident that the former has more chestnut-brown in the back, and a darker wash on the sides of the neck, but it is almost impossible to distinguish the two without shooting them, unless one can get near enough to see the color of the legs. Dr. C. W. Townsend has called my attention to the fact that the legs of the Least Sandpiper are greenish-yellow, while the Semipalmated Sandpiper has black legs.
Hoffmann – A Guide to the Birds of New England and Eastern New York (1904)