According to a 2019 study conducted by leading ornithologists from U.S. and Canadian government agencies, North America has 29% fewer birds than in 1970. This means that roughly three billion birds have been lost across hundreds of species, including some of the most common feathered visitors to backyard feeders, like sparrows, finches, warblers, thrushes, swallows, and many others.
The reasons for the decline in North America’s bird population and biodiversity are complex, but some of the causes are fairly obvious. Agricultural expansion has equated to habitat loss for many grassland species, which have also suffered from scarcity due to pesticides killing the insects they depend on for food.
Several other factors have undoubtedly contributed to the massive bird loss, including broad ecological threats like pollution and climate change. In the U.S. alone, roaming outdoor cats (mostly feral or unowned) kill an estimated two billion birds yearly. Another billion American birds die after flying into glass doors or windows. Light pollution can also be seriously disorienting for birds, affecting their migration patterns with fatal consequences.
The pervasive decline has surprised ornithologists, who expected adaptable “common” species to be better suited to changing environments and food sources.
Other studies have detected similarly dwindling bird populations in many parts of the world. Yet most of the bird species that are in decline are not in immediate danger of extinction, though some species have been harder hit than others. And some are thriving, especially wetland birds like ducks and geese, as well as raptors protected by endangered species laws.
However, as bird numbers decline from generation to generation, the possibility of extinction becomes more likely. When discussing “shrinking baseline syndrome,” conservationists often point to the sudden extinction of the passenger pigeon, which was once the most abundant bird in North America, numbering at least three billion, but rapidly declined and went extinct around 1900.
The bird's the word:
- Birds play integral roles in their ecosystems, from dispersing seeds and pollinating plants to eating harmful insects. Some are predators, while others are prey, thus keeping the populations of other animals in balance.
- Bird populations in the United States and Canada are well-monitored due to the efforts of birdwatching enthusiasts and citizen scientists who take part in tallies like the North American Breeding Bird Survey and the Christmas Bird Count.
- The decline in biodiversity is unlikely to be restricted to birds. The potential loss of other creatures, like insects, could indicate a broader problem with the health of ecosystems, but, unlike birds, they are very difficult to count.
- Additional data comes from dozens of weather radar systems that can detect the size and movements of groups of migrating birds, which appear as large blobs on the radar imagery. During the 2010s, the volume of birds’ spring migration decreased by 14%.