A new analysis, published in the journal Science, reports that the number of birds in the United States and Canada has fallen by 29% since 1970. There are 2.9 billion fewer birds in the two countries now than there were 50 years ago.
The analysis is the most comprehensive attempt to date to look at the status of avian populations. The results were a shock to researchers and conservation organizations.
It is well-known that some bird species have become vulnerable to extinction, but the new study, which surveyed more than 500 species, uncovered steep losses even among such traditionally abundant birds as robins and sparrows.
There appear to be multiple causes for the steep declines. The largest ones are likely habitat loss and the wider use of pesticides. Rachel Carson’s 1962 book Silent Spring warned of the dangers of pesticides and took its title from a world that has lost its birds.
The survey includes 76% of all bird species in the US and Canada, but actually represents almost the entire population of birds. Grassland species have suffered the biggest declines by far, as a result of modern agriculture and development. Pesticides, such as neonicotinoids, make it harder for birds to put on weight needed for migration, delaying their travel.
There are a few bright spots: bald eagles are thriving, and falcon and waterfowl populations are on the upswing. These are species that have been the subject of conservation measures in recent decades.
Stopping the bird decline will require a great deal of effort to defend habitats, restrict chemicals, and redesign buildings. Without that effort, birds will continue to disappear.
Photo, posted April 1, 2012, courtesy of Barry Skeates via Flickr.