There are two sub-species or races of Dunlin that are more commonly found in North America. These are the Dunlin (Atlantic) and the Dunlin (Pacific). As the names indicate, these shorebirds are divided up by the location of the birds and the Atlantic and Pacific Oceans. Some of the obvious differences is the Dunlin (Pacific) has a lighter coloured body, whiter neck and face. The black spotted area of the lower breast and upper stomach is noticeably larger.
Dunlin are seen throughout North America and are also seen in Eurasia and Africa, depending on the time of year. This shorebird was once known as the Red-backed Sandpiper. The Curlew Sandpiper is very similar to the Dunlin and is a vagrant visitor to the North American continent. It is a bird to watch out for.
Avibase - the world bird database This site provides the user with a complete list of bird species, broken down per country, or in the example of the US or Canada, per state and province. Here, bird species names are available in other languages, a great asset to be used as a translation of foreign bird names.
ABA - American Birding Association This site represents an organization that maintains official records of all birds species that have been proven to have been seen inside the perimeters of the North American Continent and the surrounding bodies of water. Regular revised versions are posted to keep the bird list current at all times. This is the list used by all serious birders over their lifetime. You may be aware of the movie called the "Big Year". It was with this list that all the competing birders used in an attempt to set a new record as to how many bird species that could be seen by an individual birder in one calendar year.
I hope you will take advantage of these suggested websites. I have used each of them, in one way or another, throughout the years in my quest to better identify and understand our fine feathered friends.