Christmas Bird Count Confirms Some Dramatic Declines

American crows, blue jays, and black-capped chickadees showed a big decline in this year's six-county Christmas Bird Count (CBC). The count confirms the findings of two fall surveys by Audubon-Chicago Region and the Bird Conservation Network that local populations of crows and chickadees have been decimated.

The National Audubon Society has sponsored Christmas counts across the country for more than 100 years. Teams of volunteer birders scour circles 15 miles in diameter over the course of a given day and report their results. An Audubon-Chicago Region study looked at eight of these circles. Comparing 2002 numbers for eight species with an 11-year average, the study showed dramatic declines in the populations of three local bird species. American crows were down by 81 percent, blue jays by 66 percent, and black-capped chickadees by 35 percent in the Illinois counties of Cook, Will, Lake, DuPage, and Kane, and in Lake County, Indiana.

A large network of trained and dedicated bird monitors make these findings possible. "Much of what we know about the distribution and abundance of birds — and especially the dynamic nature of this — comes from sight records of amateur birders," states Doug Stotz, conservation ecologist and ornithologist at the Field Museum of Natural History. A decline in chickadees, confirmed by the CBC analysis, had not been noted anywhere else in the country.

"The striking declines in some species, the lack of declines in other species with similar diets and habits, and the concentrations of the declines in the areas where humans were hardest hit by West Nile virus — strongly suggest that the virus is the cause," states William Moskoff, professor emeritus of economics and biology at Lake Forest College, and author of the Audubon report. Moskoff's analysis ruled out normal annual fluctuation in the numbers — due to such things as weather and number of observers — as a cause of the declines.

According to Kevin McGowan, an ornithologist with the Cornell Lab of Ornithology, crows may continue declining as more birds are exposed to the West Nile virus. The number of breeding crows, however, may stay relatively stable even with crow numbers cut in half. Young adults who previously assisted parents with nest duties may now move into newly open breeding areas. But young born last year won't breed for three or four more years.

"It will be interesting to see if the Spring Bird Count and censuses done next summer show the continued declines," Stotz noted, "or whether this will have been a one-year deal. The summer censuses will be especially interesting because it will be our first chance to see if some of the more sensitive migrant species such as ovenbirds and rose-breasted grosbeaks may have been affected."

Not all species showed similar declines. The study also examined other year-round resident landbirds — mourning doves, American goldfinches, downy woodpeckers, Northern cardinals, and white-breasted nuthatches. All of these species showed increases over the 11-year average at the 2002 Christmas Count.