Selected CBC data

Most Numerous Species Summary by Species Summary by Year

Global Warming?

Quite a few species whose winter ranges once ended just south of us are now being seen more regularly or in larger numbers on the count. This trend is more likely due to a change in seasonal distributions than to population increases. Good examples are .. Snow Geese, Hooded Mergansers, Common Mergansers, Great Blue Herons, Eastern Bluebird, American Robin, Fox Sparrow, and White-throated Sparrow.

Rough-legged Hawk numbers have plummeted since the early eighties. This species is a winter resident, so perhaps the recent milder winters have resulted in fewer birds coming this far south.

West Nile Virus

American Crows suffered a dramatic decrease in 2002 which corresponds to the arrival of the West Nile virus in northern Illinois.

Pheasants and Coyotes

Ring-necked Pheasants have undergone a gradual decline since the mid nineties. This is probably due to an increase in local coyote populations which occurred at about the same time.

Rising populations

Canada Geese dramatically increased their numbers through the eighties to become the most abundant species in the count circle. Since then the numbers have remained stable despite large year to year fluctuations.

Cooper's Hawk numbers have increased dramatically since the early nineties. This reflects increased numbers throughout the year.

Both Herring and Ring-billed Gulls increased sharply during the early nineties.

Mourning Doves and Red-bellied Woodpeckers increased their numbers dramatically in the late nineties.

The House Finch Invasion

Purple Finches declined sharply in the late eighties this is about the time when the closely related House Finches expanded its range into the region.