Birds turned out to be a good indicator for several reasons. Different species of birds prefer different environments. So if you find many water-loving birds and few birds adapted to drier habitats, that's an indication that the wetland environment is thriving. Birds are also fairly easy to track. The problem is there aren't many good records of butterflies and insects in an area.
Birders also tend to keep very detailed records of what they see.
Working with Professor Styer, Coleman learned to identify species commonly found in the Greater Cincinnati area. Then, he tracked bird occurrences in five Indiana and Ohio wetlands as well as three Cincinnati parks for a dry land comparison. Coleman used his own observations as well as the records of well-known birders. With Styer's help, the two then developed a mathematical formula which can be used to evaluate the ecological condition of wetlands. When they tested the model, they found significant differences in the bird populations of dry areas such as Mount Airy Forest and French Park and wetland areas such as the Oxbow region near the Indiana-Ohio border.