The following is a guide for beginning shorebird watchers.  It assumes that you are:
    a) interested in sorting out sandpipers
    and
    b) don't already have a fairly good grasp of the process

If you know enough about shorebird identification to critique this website, then you
probably don't need it.  I am also relying heavily on the sameness principle
which assumes that any shorebird one is likely to see is most probably a commonly
occurring one (Paulson 1993).  Since most birders are interested in finding new species
which by definition are different, any birder, independent of their experience, will
find things that look different if predisposed to do so.  The sameness principle predicts
that even if it looks different, it is probably a variant of a commonly occurring
species.  There is great value in making the assumption that a bird is common until
proven otherwise (rather than uncommon until proven otherwise).  Becoming very
acquainted with the range of variations in the few common species, before tackling
the less common ones, will help keep the wolves from your door.

This site assumes you own at least one good bird guide that you can look at while
reading through the flow charts and that you are looking for shorebirds in North
America somewhere west of the Rocky Mountains and south of the 49th parallel.

Information you need to collect (by whatever means suits you) while looking at
shorebirds:
    1. What is the date- since probability of occurrence depends on time of year this
        is a remarkably useful way to eliminate possibilities.
    2. How many are there- the sameness principle predicts that the more there are
        the more likely they're common ones.
    3. What they're standing on- some shorebirds are more habitat specific than others.
    4. Calidris sizes- which only work when comparisons are possible
                            Small = Western Sandpiper sized or smaller
                            Medium = Sanderling or Dunlin
                            Large = not covered at this site (knots, pects etc)
    5. Leg color
    6. Webbed (partially webbed, actually) toes- not always easy to see, but useful.
    7. Bill shape- is it straight or curved; tapered or uniform; thick or thin.
    8. Breast-  is it speckled, smudgy or clear.
    9. Back- does it have bright "vee" shaped braces; do the feather tips look rounded
        or pointy.

As you sort through flocks of the four most common species look for transitional
individuals.  Overtime birds molt out of one plumage and into another and will show
some bits of one description and bits of another.  These transitional birds will look
different and are very likely the main source of misidentification errors.

Four most common medium to small species

Legs green to greenish-yellow

small bill often droopy always brown, usually looks hooded can have very bright cream colored braces possible just about any time of year,    usually in wet green places (algae    mats, flooded fields) Least Sandpiper

Legs not green to greenish yellow

small longish droopy bill webbed toes either plain medium gray-brown (fall/winter) or  brown with black speckling on breast (spring) or  grayish-brown with rufous vee braces  on back (fall youngsters) unusual in winter east of Coast Range Western Sandpiper medium long droopy bill either plainly dark grey-brown (winter) or red-brown with distinctive black belly (spring) unusual between May 31 and Sep 1 Dunlin medium straight bill with little or no taper either very pale with black shoulders (winter) or  varying amounts of rufous on head,  breast and back (spring) unusual off sandy beaches or east of  Coast Range Sanderling

Next most common species if you've tried as hard as you can to follow the sameness
principle, but the bird (and it's more likely to be bird than birds) just won't go into one
of the common pigeon holes....
 

Looks like a big Least Sandpiper  with dark legs (that is, bigger than a Western, but smaller than Sanderling)	Baird's Sandpiper
Same size as a Western but lacking  the rufous vee braces (or much rufous  in the back at all).  Back feathers often look smallish, rounded and scale- like. Bill thick at base and straight.	Semipalmated Sandpiper

Species that you're probably not ready for if you need these flow charts
(and unlikely to be taken seriously about by others if your description looks
anything like the very abbreviated one's provided below)
 

Green to greenish-yellow legs

small Looks impossibly like a Least Sandpiper, but with marginally longer toes. Long-toed Stint small Totally lacking in any field marks (which, in theory, should make it pretty easy to  identify). Temminck's Stint

Look kind of like a Least Sandpiper some parts of the year (but having dark legs) and kind of like a Western at other parts of the  year, but without webs between toes.

small and short-legged Rufous hood or lacking brightly contrasting braces Red-necked Stint small Very much like a Least  Sandpiper, but with white  throat or  Like little tiny Sanderlings with no shoulder bar Little Stint Looks like a Western Sandpiper wearing a Pectoral Sandpiper's bill Broad-billed Sandpiper Looks like a cross between a  Western Sandpiper and a Platypus Spoon-billed Sandpiper Sanderling sized with a white rump White-rumped Sandpiper Looks kind of like a Dunlin with a white rump Curlew Sandpiper

References
Chandler, R.J. 1989. North Atlantic Shorebirds.

Hayman, P., J.Marchant and T. Prater. 1986. Shorebirds: an identification guide.

Paulson, D. 1993. Shorebirds of the Pacific Northwest.

Rosair, D. and D.Cotteridge. 1995. Photographic Guide to Shorebirds of the World.

Sibley, D.A. 2000. Sibley Guide to Birds.