According to the Audubon Society's analysis of forty years of multiple sources of data, many common birds are suffering steep population declines. Since 1967, the average population loss has been 68 percent, while some lost as much as 80 percent.
Some of the birds include various common sparrows (averaging over 60% loss), whippoorwills (57%), boreal chickadees (73%) and northern bobwhite quails (82%). Changes in farming and habitat loss are prime suspects in these losses.
Massive, fast losses across such a wide spectrum of common bird species alarms scientists. "Backyard birds" are a bellwether of the state of the planet's overall health, and point to serious problems that affect many other species, including humans.