Waterfowl Aerial Inventories

In the fall of 1938 and in subsequent years, Frank C. Bellrose traveled by car and boat with binoculars and spotting scopes to record waterfowl numbers 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.

The Illinois River valley from Spring Valley to Grafton and the Mississippi River valley from Alton to Moline have been periodically inventoried in the fall by INHS since 1948, and various other areas of waterfowl habitat have been monitored over the years.

Approximately 214 miles of the Illinois River and 272 miles of the central Mississippi River are aerially inventoried for waterfowl weekly from September through late December.

The purpose of the aerial inventories conducted by INHS 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 by the database of any other state.

Beginning in fall, 2002, the number of areas aerially inventoried for waterfowl were reduced. Analyses of recent aerial inventory data indicated that 37 percent of the 54 areas inventoried on the Illinois River provided an average of more than 91 percent of the peak population of total ducks for the Illinois River region. For the central Mississippi River, 38 percent of the 39 areas inventoried held an average of 94 percent of the peak population of total ducks inventoried. Based on these analyses we currently aerially inventory 20 locations on the Illinois River and 15 locations on the central Mississippi River.