Currently there is only one species of willet (Tringa semipalmatus). Some birders recognize two subspecies, the western inornatus and the eastern semipalmatus, and believe the subspecies should be designated as separate species. Species (and genus) designation decisions are made by the American Ornithologists’ Union (AOU) Checklist Committee and are based on published research. Currently the status of the willet is being considered by the Committee.
The eastern willet is about 10% smaller than the western subspecies. It also has approximately a 15% shorter bill and legs that are also about 15% shorter. The bill of the western willet, in addition to being longer, is thinner and more often upturned.
The western willet is paler (more grey) in all plumages. The eastern is more heavily barred on the chest and back, particularly in breeding plumage. The distinctive black and white striped wing pattern seen in flight has a broader white stripe in the western inornatus.
Western inornatus willets winter in fresh and saltwater marshes along the Pacific Coast. This subspecies moves inland to breed in freshwater and alkaline marshes. The eastern semipalmatus inhabits Atlantic and Gulf Coast saltwater marshes. They do not move inland to breed. There is no contact on between the two populations on the breeding grounds nor do their ranges overlap.
The subspecies can also be differentiated by their calls. Although it is difficult for most people to discern the difference, research shows the two groups easily distinguish between recorded calls. All songs and calls of the western subspecies are lower pitched than those of the eastern.
I expect that before long there will be two species of Tringa willets – the eastern semipalmatus and the western inornatus. This would not be the first taxonomic name change for the willet. Previously the willet was considered the only species in the genus Catoptrophorus, but in 2006 the AOU moved it to the genus Tringa.
No matter what it is called, Leonard and I always await the return of the willets each spring, usually around April 1st in our area. This willet was photographed along the Bieber/Lookout Road in Lassen County CA.