BOSTON — New data show the populations of some of America’s well-known birds in a tailspin, thanks to the one-two punch of habitat fragmentation and, increasingly, global warming. From the heartland’s whippoorwills and meadowlarks to the Northern bobwhite and common terns of the nation’s coasts, 20 common bird species tracked by the National Audubon Society have seen their numbers fall 54 percent overall since 1967, with some down about 80 percent, the group reported Thursday. Most of the trouble lies with loss of bird habitat, and has for decades, due to expanding agriculture and suburban development. The Rufous hummingbird’s population has fallen 58 percent due to logging and development in its Pacific Northwest breeding range – and in its winter range in Mexico. The same thing has happened to whipporwills, whose numbers are down 57 percent due to loss of their forest habitat. At the same time, scientists say changes in migration patterns due to global warming are emerging, too. ‘Habitat loss is still the major concern,’ says Greg Butcher, Audubon’s bird conservation director in an interview. ‘But we’re also seeing increasing impact from large-scale problems like global warming.’ Thursday’s study updates and expands earlier efforts: […]