You'll want a binocular that works well where these birds hang out--in open terrain, at greater distances, and under favorable lighting conditions. All of these factors make high magnification binoculars both workable and desirable. If you're seriously interested in viewing shorebirds and waterfowl, you are sure to find yourself out in the rain or sleet along with these birds. Since some of the most interesting sightings are made during inclement weather, you'll want to consider waterproof binoculars.
Practically any binocular can be used for viewing shorebirds, however full-size binoculars are suggested due to their light gathering capability. Binoculars with objective lenses of 30mm up to 42mm sizes gather sufficient light and are very portable. A 50mm binocular may provide brighter images, but because of the large objective lenses, you'll want to consider the size and weight of the binocular.
Viewing birds from small boats like canoes and kayaks is becoming increasingly popular. If you plan to use your binocular from a small watercraft, you'll appreciate waterproof binoculars that can survive an accidental dunking and keep going strong.