Illinois Department of Natural Resources
August 2021
August 2, 2021
Photo by Michael R. Jeffords.

Illinois Cooper’s—Both Residents and Migrants Depending on the Season

By Robert J. Reber

Illinois has both a resident breeding population throughout the state as well as spring and fall migrants. Spring migrants usually begin coming through in March, although some have been noted as early as mid-February. Fall migration starts as early as August. 

A reddish brown, gray, and white hawk perched on a tree branch. A blue sky is in the background.
Photo by Pete Nuij.

How does one tell the difference between a resident or a migrating Cooper’s hawk? Where do migrants come from and where do they go? About the only way such questions can be answered for sure is by identifying individual birds via tagging and tracking movements with state-of-the-art electronic methods. Such endeavors are expensive, take considerable effort, and are sometimes not a high priority task to do. 

Reliable information on the trends and movements of bird species is extremely important when prudent management suggestions and decisions have to be made. For example, state-threatened or -endangered classifications (listings) are usually based on the resident breeding population assessments as was the case for placing Cooper’s hawks on the state endangered list in 1977.

In lieu of state-of-the-art individual bird or animal identification, much information about numbers and movements of wildlife species is very anecdotal in nature, such as the bobcat sightings reported by deer hunters in the field. While valuable, such information does not always account for the variable conditions under which observations were made. Still, anecdotal accounts are about all we have to go on much of the time.

A graph indicating the population trend for Cooper's hawks as estimated by the Illinois Spring Bird Count data.

Even at a local level, an observation may be biased depending on the time of day, weather conditions at the time, or what habitat was being observed—just to name a few of the often-occurring variable factors. For example, a resident population of overwintering birds may have appeared to decrease when some of the local birds moved to more protected habitats such as heavily timbered river bottomlands as is often the case for red-headed woodpeckers. A person not aware of such behavior may conclude that the species is declining. Or, some birds in Illinois do shift a bit south but remain in state to overwinter, even though they don’t enter a full-blown migration to the Gulf States. 

Historically, such questions about trends and movements of species such as Canada geese and white pelicans were somewhat easier to answer because of their large body size, numbers and established traditional habitats. Flocks of flying Canada geese are easy to see, track and estimate flock size. Not so for smaller birds such as Cooper’s hawks which are fewer in number, harder to track, and do not migrate in large groups. Even now we no longer can rely on historic traditional knowledge. For example, Canada geese have taken to overwintering in shopping mall retention ponds that remain unfrozen in winter. 

A graphic with a photo at the top with a bird guide book opened to the owl section with a pair of binoculars sitting on top of the book. Below the photo is some text describing the online research collaborative tool, eBird.
Interested in participating in eBird?
Check it out here!

Where and how can the backyard birder gather data, be it somewhat sketchy in nature, to at least assist? The Illinois Spring Bird Count, conducted the first Saturday in May, gives some sense of the local breeding populations as well as migrant activity. This timing usually corresponds to peak spring migration. The National Audubon Society’s Christmas Bird Count is a 24-hour count between December 14 and January 5. You can volunteer to count a defined area. The Society gives volunteers some training and guidelines to make gathered data more valuable. Another option to participate in this Audubon count is to record all the birds that visit your backyard feeder on that day. 

Of course, a backyard birder doesn’t have to be part of an undergoing event. Simply keeping a daily log of species that visit your feeder can be worthwhile and entertaining. The parameters you set for collecting can be as simple or as detailed as you wish. Visit the eBird Cooper’s Hawk page for additional information status and trends. Be all that as it may be with a lack of hard scientific fact, most current data suggest a somewhat brighter future for the Cooper’s hawk’s world, unless perhaps you happen to be the slowest dove at the bird feeder.

Robert J. Reber is an emeritus faculty member in the Department of Food Science and Human Nutrition of the University of Illinois at Urbana–Champaign. He has been a lifelong student of many aspects of the Natural World, including archaeology. Bob has served as a managing editor and author for publications such as “The Illinois Steward” magazine and the “Illinois Master Naturalist Curriculum Guide.”