For the Birds Radio Program: Trends in bird populations
Why don’t we see as many birds as we used to? (4:01) Date verified.
Trends in Bird Populations
(Recording of a Western Meadowlark)
For the past few years people have been asking me why there don’t seem to be as many birds around as there used to be. It’s easy to chalk up their concerns to simple nostalgia for the old days—to think that their memories of abundant bird life are akin to memories of bigger snowfalls in the olden days. There were few reliable counts of birds taken in the 1800’s, though anyone who has ever read the “Little House” series of books by Laura Ingalls Wilder knows darn well that there must have been a lot more birds back then than there are today.
There was no effort to accurately count breeding bird populations in North America until just 23 years ago, when my personal hero, Chandler Robbins, of the U.S. Fish and Wildlife Service, started the North American Breeding Bird Survey. Every year since 1966, 2,000 skilled volunteers have surveyed a network of permanent roadside transects spread throughout the United States and Canada, using standardized techniques, in an effort to learn exactly what is happening to bird numbers. Now it is possible to look at their data to find out whether bird numbers are dropping everywhere, or whether their apparent losses are in fact simply a very localized phenomenon.
According to the Breeding Bird Survey data, in both Wisconsin and Minnesota between 1966 and 1986, the populations of 34 species of birds declined more than 2% every year. The declines were greatest in waterfowl and other game birds, and grassland species, like bobolinks, meadowlarks, and native sparrows. In Minnesota the most notable decline was in the Red Crossbill, which has declined by an average 27% every year over the 20-year period. The Ruddy Duck showed another dramatic decline–over a 10% drop every year. Worst hit in Wisconsin was the Dickcissel, which showed an average annual decline of 14%, and the Grasshopper Sparrow, which dropped over 12% each year.
Cowbirds, nest parasites which are considered a major factor in the declines of some forest-nesting species, are themselves slowly decreasing now–perhaps because their hosts are declining. In both states their population has dropped by over 2% each year.
Naturally some species are increasing. Ring-billed Gulls have been increasing an average of about 8% in both states over the period. Bald Eagles are up by about 18% every year in Minnesota, where small lakes are less subject to pollution because of the Boundary Waters area than in Wisconsin. In that state eagles are up a mere 2% a year. Crows seem much more abundant now than they ever did, but that’s because they are now exploiting the urban habitat, bringing them to the notice of people who never noticed them back when they were wilder. Overall crow numbers have increased over 2% each year in Minnesota, but in Wisconsin the numbers have remained pretty stable over the period—apparently urban areas gained no more crows on average than wilder areas lost.One bird I expected to have dropped dramatically, the Scarlet Tanager, apparently was just as rare 23 years ago as it is now, because its numbers have hardly changed at all.
If you’re interested in seeing the Breeding Bird Survey data from Minnesota or Wisconsin in greateer detail, drop me a line, in care of this station.
(Recording of a Western Meadowlark)
This is Laura Erickson, and this program has been “For the Birds.”