In the fall of 1938 and in subsequent years, Dr. Frank C. Bellrose traveled by car and boat with binoculars and a spotting scope to record waterfowl abundance from various vantage points in the Illinois River valley. When Bellrose initiated experimental aerial inventories in the fall of 1946, he noted that the time required to inventory the Illinois Valley was reduced from a week to a day and that a large part of the Mississippi Valley could be included in the one-day flight. Since 1948, waterfowl aerial inventories have been conducted by the INHS.
Approximately 214 miles of the Illinois River, from Spring Valley to Grafton, and 272 miles of the central Mississippi River, from Alton to Moline, are aerially inventoried for waterfowl weekly from September through early January.
The purpose of these aerial inventories is not to acquire complete counts of waterfowl numbers within specific geographic areas but to estimate the number of each species in order to provide an index of temporal changes within and among years and to document the distribution of the species throughout the monitored regions. Because of the efforts of the INHS with the long-term support of the Illinois Department of Natural Resources, the annual inventory data on numbers and distribution of migratory waterfowl in Illinois is unequaled.
We aerially inventory 20 locations on the Illinois River and 15 locations on the central Mississippi River weekly. Flights are generally scheduled for each Monday beginning in early September and once a flight is completed, results are posted as soon as possible.