Three types of hibernacula have been designated depending on the amount of use each receives from year to year. Priority one hibernacula are those that consistently have greater than 30,000 Indiana bats hibernating inside each winter. Priority two hibernacula contain 500 to 30,000 bats, and priority three hibernacula are any with fewer than 500 bats. At least 50% of Indiana bats are thought to hibernate in the eight priority one hibernacula, which can be found in Indiana (three), Missouri (three), and Kentucky (two). Estimates of hibernating populations in 2001 suggest that priority one hibernacula have experienced a 48% decline since 1983. Overall, populations have fallen around 57% since 1960 across all hibernacula.