Decline and Recovery of an Isolated Prairie Chicken Population
The greater prairie chicken, Tympanuchus cupido pinnatus, is a grassland-dependent bird that formerly numbered in the millions throughout the Midwest. Now, its population and habitat are greatly reduced throughout its former range. Illinois for example, was originally 60 percent suitable habitat, but today less than 0.01 percent of the state’s area is suitable prairie chicken habitat. In the 19th century there were several million birds in the state; by 1962 there were about 2,000 birds scattered in patches in the southern part of the state; by 1994 about 46 birds remained in two remnant populations in Jasper County, Illinois, 640 kilometers away from the nearest viable population.
The eastern subspecies Tympanuchus cupido cupido, also known as the heath hen, has been extinct since 1931, and Attwater's prairie chicken, Tympanuchus cupido attwateri, which is restricted to Texas, is near extinction.
If one were to write an instruction manual on how to drive a species to extinction, the first order of business would be to deprive it of places to live and reduce the population size. Theory and practice tell us that there is a minimum number of individuals below which a population is not likely to endure. One of the main reasons is inbreeding depression, whereby adults are less likely to produce viable offspring, and the offspring that are born are less likely to survive and thrive.
In 1992 prairie chickens were brought into Illinois from outside populations, and both the fertility of eggs and the success rate of hatching increased, indicating there was indeed a genetic component to the long term decline of the population.
We spoke with Dr. Jeffrey Brawn about this project and how it applies to conservation efforts in general.