Human development and beach tourism have drastically reduced the number of piping plovers, a small shorebird that lives east of the Rocky Mountains.

The plover is one of 59 birds in the continental U.S. cited as a "red list" species of greatest concern in a new report by the National Audubon Society and the American Bird Conservancy.

The report says efforts to protect the plovers' beachfront nesting grounds, which have successfully increased bird numbers in some areas, must be expanded to protect the species.

An additional 39 birds species found in Hawaii were placed on the red list, while 119 species in the continental U.S. were put in the "yellow" category of seriously declining or rare species.

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