A study published in the journal Science reveals that since 1970, bird populations in the United States and Canada have declined by 29 percent, or almost 3 billion birds. The results show tremendous losses across diverse groups of birds and habitats - from iconic songsters such as meadowlarks to long-distance migrants such as swallows.
"These data are consistent with what we're seeing elsewhere," said coauthor Peter Marra, former head of the Smithsonian Migratory Bird Center. It's urgent to address ongoing threats, both because the domino effects (多米诺效应)can lead to thedecayof ecosystems that humans depend on for our own health and livelihoods and because people all over the world cherish birds in their own right. Can you imagine a world without birdsong?"
Evidence for the declines emerged from detection of migratory birds in the air from 143 NEXRAD weather radar stations across the continent in a period spanning over 10 years as well as from nearly 50 years of data collected through multiple monitoring efforts on the ground. Citizen-science participants also contributed a lot, for the analysis included citizen-science data from the North American Breeding Bird Survey coordinated by the Canadian Wildlife Service- the main sources of long-term, large-scale population data for North American birds.
The study noted that the largest factor driving these declines is likely the widespread loss and degradation of habitat, especially due to agricultural intensification and urbanization. Other studies have documented death from predation (捕食)by domestic cats; collisions with glass, buildings, and other structures; and pervasive (普遍的)use of pesticides associated with widespread declines in insects, an essential food source for birds. Climate change is expected to compound these challenges by altering habitats and threatening plant communities that birds need to survive.
"It's a wake-up call that we've lost more than a quarter of our birds in the U.S. and Canada," said coauthor Adam Smith from Environment and Climate Change Canada. But the crisis reaches far beyond our individual borders. Many of the birds that breed in Canadian backyards migrate through or spend the winter in the U.S. and places farther south - from Mexico and the Caribbean to Central and South America. What our birds need now is an historic, hemispheric effort that unites people and organizations with one common goal: bringing our birds back.
