It is the nesting season for American oystercatchers, the harlequin-colored shorebirds with large reddish-orange bills.

Like piping plovers, the migratory birds return to the Vineyard in the late spring and nest in coastal areas. As the name suggests, the birds eat bivalve mollusks.

Ten years ago, surveys showed the American oystercatcher population was in decline. A coalition was formed to protect the birds, and the population has rebounded; an aerial survey in 2013 found 11,200 birds. In Massachusetts, they are a species of concern.

Here is a rare closer look at four American oystercatcher nests on the South Shore last week. Shorebird nesting areas are restricted. The photographer was accompanied by a shorebird monitor.