Early on a cool June morning, heavy dew lies on the grass of rolling farm country somewhere in Tennessee, or Missouri or Pennsylvania. Small patches of fog hang in low-lying pockets of these fields.

In the distance, hardworking farmers are starting their day. Farm equipment clangs, tractors roar to life and voices lining out the day's work drift on the air.

This pastoral scene is repeated thousands of times each morning across rural America. But something is missing: the exuberant "Bob bobwhite!" call of the bobwhite quail that for generations was the soundtrack to summer mornings.

Once abundant across the eastern U.S., bobwhite populations have declined by 85%. Calculations suggest that the remaining population could be cut in half within the next decade.

Many other grassland birds, such as grasshopper sparrows and eastern meadowlarks, also are disappearing at an alarming rate.

Taken together, grassland birds have experienced the worst population declines among all North American birds.

Why is this happening? In a word, habitat.

Native grasslands in the U.S., especially those east of the Great Plains, which once covered millions of acres, have almost completely disappeared. Some have been converted to croplands.

Others have been allowed to grow back up into forests, where shade from the tree canopy prevents the growth of these grasses.