The Illinois and Mississippi river valleys are major migration and wintering areas for nearly 30 species of waterfowl in the Mississippi Flyway. The INHS, with support from the IDNR and the Federal Aid to Wildlife Restoration Fund through the U.S. Fish and Wildlife Service (USFWS), has conducted aerial inventories of waterfowl along the Illinois and Mississippi rivers since 1948 (flown each year but 2001). This undertaking represents the longest known inventory of waterfowl, preceding even the USFWS breeding waterfowl counts and mid-winter inventories established in 1955. Therefore, 65 years of data exist on fall-migrating waterfowl for these critical ecoregions and has vastly improved our understanding of the chronology of migration, the effects of refuges, and the distribution of waterfowl in Illinois.
Data from this project was published in 1999: Havera, S.P. 1999. Waterfowl of Illinois: Status and Management (and Abbreviated Field Guide): INHS Special Publication 21 and INHS Manual 7. Ill. Nat. Hist. Surv. Rep. No. 358:5, 7.
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 23 locations on the Illinois River and 18 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.
INHS Aerial Inventory Observers, 1948 – Present
2020 – 2021 INHS Waterfowl Aerial Inventory Data
Central Mississippi River
The Illinois and Mississippi river valleys are major migration and wintering areas for nearly 30 species of waterfowl in the Mississippi Flyway. Additionally, these areas provide significant recreational opportunities (e.g., waterfowl hunting and bird watching) and economic support for the local and regional economies. Frank Bellrose of the Illinois Natural History Survey (INHS) began aerial surveys of waterfowl during autumn migration in the Illinois and Mississippi river floodplains in 1948. Initially, these flights were conducted weekly from October through mid-December, and the winter inventory in early January was added in 1955. Today, INHS surveys, with support from the Illinois Department of Natural Resources (IDNR) and the Federal Aid to Wildlife Restoration Fund through the U.S. Fish and Wildlife Service (USFWS), are conducted from early September through early January to include early teal migration and overlap with the USFWS Midwinter Waterfowl Survey in early January. This collaborative undertaking between the INHS and IDNR represents the longest known continuous survey of waterfowl in North America, preceding even the USFWS breeding waterfowl surveys, which were established in 1955.
Why Are Surveys Important?
Data from aerial inventories are used to direct waterfowl management, conservation planning for habitat acquisition, ecological research, and for public outreach. There are many important private, state, and federal waterfowl areas and refuges within these river floodplains, such as the Two Rivers and Great River National Wildlife Refuges (NWR), the Illinois River National Wildlife and Fish Refuges, and Keokuk Pool. Aerial survey results are frequently requested by and circulated among federal and state personnel. Specifically, the IDNR relies on these inventories to guide the establishment of hunting season dates, zones, and other regulations and to prioritize wetland habitat acquisitions. Previously, this database has been used by the Mississippi Flyway Technical Section and Council to monitor abundance and distribution of migrating waterfowl, especially canvasback, mallard, and northern pintail. The Upper Mississippi and Great Lakes Region Joint Venture uses survey data to assist in parameterizing carrying capacity models and identifying priority regions for conservation. Requests for inventory information are received annually from state, federal, and private-sector entities to be used for projects such as Environmental Management Programs, scientific publications, theses and dissertations, formal presentations, education, newspaper and magazine articles, and many other uses.
Considering the varied uses of the data and the fluctuating population levels of many waterfowl species, continuation of the monitoring of waterfowl populations at a baseline level is desirable to maintain the consistency and extension of the long-term data set into the future. Monitoring the distribution and relative abundances of waterfowl and waterbirds over time is critical to detect changes in migration corridors and can be used to identify research needs and indicate changes in habitat quality. Future threats to wildlife habitats and ecosystem services provided by rivers, lakes, and wetlands surveyed each year (e.g., climate change modeling, habitat suitability modeling, flood prediction modeling) may be better understood and their effects predicted using this unique and long-term dataset.
How Are the Surveys Conducted?
Weekly during autumn, a highly-skilled biologist and pilot use a fixed-wing aircraft to visit wetlands and lakes which historically hold >90% of the waterfowl and other waterbirds present in the Illinois and central Mississippi river valleys. Along the Illinois River, these sites are located between Hennepin and Grafton, IL and from Grafton to New Boston, IL along the central Mississippi River. Since 1948, only 4 different biologists have conducted the aerial surveys using standardized counting methods. The pilot often makes two passes around each site during each survey. During the first pass, the biologist estimates the number of birds present at each site. On the second pass, the biologist estimates species composition within each site. Sometimes, individual sites hold more than 100,000 waterbirds and multiple passes may be required for the biologist to count birds and assign species composition. Because it is important to enumerate waterbirds by species, the pilot often circles between 200 and 300 feet above ground level, which requires skill and special permission from the Federal Aviation Administration.
What Should You Do If You See the Plane?
If you see our biologist counting ducks, feel free to watch and wave. If you notice our airplane as you are boating or driving near large groups of waterfowl, we would appreciate you stopping, when it is safe to do so, to prevent birds from flushing in front of the airplane. After the count is completed, our biologist might even have time to wave to say “thanks!”
Do the Surveys Affect Waterfowl Distribution?
We have little information to indicate that ducks and geese leave areas en masse following our surveys. In fact, we have conducted ground surveys simultaneously with aerial surveys along the Illinois River and determined that approximately 13% of waterfowl exhibited a response to the airplane and that only 6% of waterfowl abandon an area and did not immediately return during or following an aerial survey. Only 8% of ducks exhibited a response during aerial surveys and <3% abandoned survey areas. Typically, aerial grid surveys last <4 minutes/site. Anecdotally, other sources of disturbance (e.g., raptors such as eagles, boats, hunting groups, barges, etc.) have a much greater effect on distributions of waterfowl and other waterbirds during autumn than do aerial surveys.
Why Are Surveys Conducted Multiple Times in One Week?
During autumns and winters of 2014–2016, the INHS is conducting additional aerial surveys of waterfowl along the Illinois River to help assess new methodologies for improving this long-term project. Traditional aerial surveys conducted along the Illinois and Mississippi Rivers provide an index of population size rather than an actual population size. New methods may allow researchers to determine actual population sizes within our survey area along with estimates of variance (i.e., confidence intervals around those estimates). However, changing to a new methodology may have implications for the use of 65 previous years’ worth of index counts. Thus, we are conducting a new “grid” survey following each traditional survey to ensure that we maintain a relationship between the new estimates and those from previous years. Each week, we will conduct aerial surveys of approximately sixty 1-mi2“grids” within the Illinois River floodplain from Hennepin to Meredosia, IL. These grids will be randomly placed within the study area and will include portions of traditional “core” survey locations (e.g., Chautauqua NWR, Grass Lake, Rice Lake, Meredosia NWR, etc.) and other “random” survey locations (e.g., drainage and levee districts, Anderson Lake, Pekin Lake, etc.). The aerial grid surveys will be flown each week following the traditional inventory-style aerial survey. Some traditional “core” locations may be surveyed 2-3 times in one week due to random chance and survey protocols. On a small subset of these survey areas, surveys may be conducted twice in one day (e.g., morning and afternoon) in order for researchers to estimate detection probabilities – that is, to correct population estimates for birds not detected during one pass over an area. Other areas may be surveyed only once per week or once every several weeks. This study will produce estimates of detection probability and population size in our study area which will be useful to a wide variety of conservation planners and stakeholders. We will produce thunderstorm maps useful to the general public to interpret and track the abundances of waterfowl through the region during autumn. We will provide a linkage (e.g., conversion factor) between estimates produced by new aerial surveys and counts produced using traditional methodology in order to facilitate simultaneous reference from historical inventory counts and future survey estimates.
Questions or Concerns?
If you have questions or concerns regarding our aerial surveys, please contact Principal Investigators Heath Hagy or Aaron Yetter at the Forbes Biological Station (217-332-DUCK). More information and a weekly aerial surveyor’s blog can be found at https://www.facebook.com/ForbesBiologicalStation/.
Traditional aerial surveys conducted along the Illinois and Mississippi Rivers provide an index of population size rather than an actual population size. New methods may allow researchers to determine actual population sizes within our survey area along with estimates of variance. However, changing to a new methodology may have implications for the use of 65 previous years’ worth of index counts. Thus, we are conducting a new “grid” survey following each traditional survey to ensure that we maintain a relationship between the new estimates and those from previous years. Each week, we will conduct aerial surveys of approximately sixty 1-sq mi “grids” within the Illinois River floodplain from Hennepin to Meredosia, IL. These grids will be randomly placed within the study area and will include portions of traditional “core” survey locations (e.g., Chautauqua NWR, Rice Lake, Meredosia NWR, etc.) and other “random” survey locations (e.g., drainage and levee districts, Anderson Lake, Pekin Lake, etc.). The aerial grid surveys will be flown each week following the traditional inventory-style aerial survey. Click here for more information.