The Willet loudly heralds the arrival of spring from aloft with its ringing “pill-will-willet” call, accompanied by flashing wing-beats. A medium-sized, moderately abundant shorebird, the Willet remains brown and inconspicuous until it opens its wings, displaying an unusually broad white wing-stripe that runs across the primaries and secondaries, bordered in black. This species has one of the greatest latitudinal ranges of temperate breeding shorebirds in North America – from the Canadian Maritimes to Venezuela. This species is composed of 2 disjunct breeding populations differing in ecology, in morphology, and subtly in vocalizations. Populations breeding in inland, primarily freshwater habitats of the western US and Canada belong to the subspecies Tringa semipalmata inornatus, or Western Willet. Populations breeding in the marshes of the Atlantic coast, from New Brunswick to Tamaulipas, belong to the subspecies C. s. semipalmatus or Eastern Willet. The two breeding environments differ in several characteristics. Eastern Willets often have abundant food resources but limited nesting habitat, while Western Willets often have abundant nesting habitat but unpredictable food resources, depending on wetland availability and drought. Ambient sound also differs between the breeding areas of the 2 subspecies, and this has resulted in a divergence in “song” characteristics. The song (“pill-will-willet“) of the Eastern Willet is emitted at a higher frequency and more rapid repetition rate than that of the Western Willet. Calls of both subspecies sound very similar to human ears, but Eastern Willets do discriminate between male songs of the 2 subspecies, responding preferentially to Eastern song. Western Willets tend to be larger and paler than Eastern Willets, with less ornate barring in their breeding plumage. These are average differences, and the 2 races overlap in these morphological characteristics.