Projects and Research
The West Tennessee Refuges Complex manages over 3,000 acres of waterfowl impoundments, and approximately 52,000 acres of bottomland hardwoods and permanent water, which provide the necessary food resources and other habitats required by waterfowl. These Tennessee refuges are located on the northern edge of the wintering grounds, and host several species of ducks and geese from October through March. During this period, selected areas are surveyed once every two weeks from the ground; however, once per year each refuge is surveyed from the air to ensure that birds in inaccessible areas are counted and to contribute waterfowl survey numbers to the nationwide Mid-Winter Waterfowl Survey. The purpose of these surveys is to document the number of waterfowl species observed as well as the number of birds utilizing the refuges, and to help natural resource professionals understand the continually changing migration patterns of waterfowl.
Many times we are asked as to how we count waterfowl. Counting large numbers of birds is a skill that is developed over many years, and is mentored from one biologist to another. Initially, an inexperienced observer is taught to recognize what a small number of birds looks like, and then to increase that number incrementally. For example, a surveyor learns what five birds look like, then ten birds, all the way up to one thousand birds. Realistically, as the number of birds to be counted rises, so does the margin of error, as it is much more accurate to count five birds than to count one thousand birds. Thus, waterfowl survey numbers are simply estimates which are highly influenced by the bias and expertise of the observer. Generally, birds do not gather in large concentrations, but are scattered in smaller groups over several impoundments. Because the birds are in smaller groups, the count is more accurate as the surveyor counts the birds in each impoundment and then combines the totals to arrive at a final number. However, with extremely large numbers, such as the estimated 90,000 ducks observed sitting together within the West Tennessee NWR Complex in 2010, the surveyor counts in one thousand duck blocks and then totals the number of blocks. Ultimately, the most important information derived from these surveys is not the actual number of birds, but the population trend, as managers need to know if bird numbers are increasing or declining, not only within one year, but also from year to year.