The expression “a canary in a coal mine” serves as advanced warning of danger, and it is a fitting phrase for a recent study that finds the United States and Canada’s massive loss of nearly 3 billion birds, or 29 percent of their bird populations, since 1970.

Overall, 10 habitats were analyzed, and findings across the board have proven worrisome. Grassland birds registered the steepest drop, with nearly 720 million lost — or over 50 percent decline — in the past 50 years. Boreal forest birds suffered a loss of 5 million individuals, while birds classified as forest generalists registered a 20 percent decline with 482 million individuals lost.

Related: Bird deaths from skyscrapers reaches into the hundreds of millions

Ninety percent of the loss has occurred among many common, widespread species — like blackbirds, finches, sparrows, swallows, warblers and other backyard favorites — all of which have significantly wide-ranging seed dispersal and pest control roles in ecological food webs for ecosystem equilibrium. Feeder birds, for instance, plummeted by an estimated 170 million, and the white-throated sparrow population lost 90 million. Other sobering data conclusions include a 14 percent decline in nocturnal spring-migrating birds in the past 10 years alone.

Habitat generalists, which are birds that thrive in more than two different habitats, similarly dropped by 20 percent, with 417 million birds gone. Another 20 percent loss occurred within the Eastern forest bird populations, which is noted for its many forest songbirds and migratory species, with an estimated 167 million individual birds lost. Unfortunately, the Western forest birds have not fared better, especially with the growing wildfire threats, thereby causing a decline of about 140 million birds. Arctic tundra birds, by reasons of warming temperatures melting permafrost in addition to dwindling food supply and nesting grounds, have suffered a loss of 80 million birds since 1970.

Of the 10 habitats surveyed, only two experienced the smallest relative declines, but their losses are still in the millions. Arid lands birds, like those in the Southwest, tallied a loss of 35 million birds. Coastal bird populations — which are menaced by increased tropical storm erosion, rising sea levels and nesting ground disturbances — documented a loss of 6 million individual birds. All this avian loss spells catastrophic shifts in the ecosystems.

What’s causing the drastic populations reductions? Climate change, habitat loss via agricultural and urban development, logging, pesticide use and the accompanying insect decline, widespread forest fires, even clearing for fossil fuel development are all important vehicles. Other direct threats include outdoor cats and skyscrapers. As for hazards faced by migratory species, these include fireworks, aircraft, light pollution causing flight confusion, the alteration of migration stops by human development and especially habitat loss. All evidence ultimately points to human influence as the driving factor to avian population decline.

On a brighter note, not all bird species declined. Wetland conservation benefited the waterfowl populations, which gained about 34 million waterfowl individuals since the 1970s. Bald eagles and other raptors increased by 15 million, largely due to the 1972 banning of DDT.

The findings were published by the American Bird Conservancy (ABC), the renowned bird conservation body in the Western Hemisphere. ABC collaborated with the Smithsonian Conservation Biology Institute, the U.S. Geological Survey and the Canadian Wildlife Service.

The overall picture is alarmingly stark, even despite the uncertainty ranges, gaps in the study and outlier gains. It is hoped the research findings will serve as a wake-up call, jolting everyone into greater awareness for the need of both bird-saving solutions and effective action.

+ American Bird Conservancy

Image via Andreistroe