Here is a Black-bellied Plover in the process of molting from breeding (alternate) to non-breeding (basic) plumage. The result is an interesting patchwork of different feather generations. At this time of year, different individuals have different combinations, some being less advanced and some more advanced than others as their molt progresses.
This is one reason why it's impossible to illustrate every possible plumage in a field guide. The solution is not to expect every bird to look exactly a picture in your book, but to spend time with the birds and get to know the common variations as they change their appearance through the seasons. In this individual, the black smudges on the underparts and face and the black centered feathers on the back are old alternate feathers which grew in last Spring. The dull, gray colored feathers are new and have recently grown in to replace the breeding (alternate) feathers. This drab feathering and will eventually dominate as molt continues. It won't take
this bird too long to look like the next bird below.
Shorebirds are migrating through from their Arctic breeding grounds. Adults usually migrate first. This Black-bellied Plover has already molted into winter (basic) plumage.
In some parts of the world this species is called the "Grey Plover." It was formerly in its own genus, Squatarola, but was merged into Pluvialis by the AOU in 1973.
Digiscoped with Panasonic DMC-LZ5 | Nikon FieldScope 3 | 30X WA | hand-held (no adapter)