The fact that bats use tunnels for hibernation is not new. In the 1930's, bat researcher Charles Mohr documented thousands of bats using several tunnels in the southern portion of Pennsylvania. Although the tunnels that Dr. Mohr documented are no longer available to bats, there are many other tunnels across the state which might be used by bats.

In 1986, the Pennsylvania Game Commission (PGC) began a multi-year study to determine winter bat populations in Pennsylvania. Now, with thirteen years of data to draw from, some trends are beginning to become noticeable. One of these trends is that bats are using the majority of the abandoned tunnels surveyed.

It is unknown exactly how many tunnels there are in Pennsylvania, or how many of them are not currently being used by either cars or trains. However, the PGC has been able to survey 25 abandoned tunnels for bats so far. These surveys took place during the winter months when the bats were hibernating in the tunnels, usually between January 1st and March 1st. Almost every year since the surveys began we have found at least one more tunnel to survey.

Surveying bats in a tunnel is not an easy job, although it is somewhat simpler than crawling through a cave to count bats. Most of the tunnels have a high ceiling, ranging up to 30 feet high, which requires the use of binoculars and a portable 12-volt spotlight to correctly identify the bats. Additionally, many of the tunnels are flooded to some degree, and in some cases can only be surveyed by canoe. Since this type of survey can only done in the winter, cold weather sometimes makes for an espicially unusual trip. Finally, given that some of the tunnels are a mile long, the result at the end of the day is usually cold, wet feet and a sore neck.

Of course, the surveys have been very productive, and we are beginning to get a picture of which bats use the tunnels and which seem to avoid them (Table 1). By far, the most common bat found was the big brown bat (Eptesicus fuscus). Of the 20 tunnels that had at least one bat, all had big browns, and typically more than 10 individuals. In 17 of the 20 tunnels with bats, it was the most numerous bat. In order to put these numbers into perspective, consider that tunnels in Bedford County and in Clearfield County are the second and fifth largest known hibernacula of big browns in the state. From the perspective of total bats, 22% of all known hibernating big brown bats in Pennsylvania occur in tunnels, yet less than 7% of all hibernation sites surveyed were tunnels.

Small-footed (Myotis leibii) bats appear to use tunnels at the same rate as any other type of hibernaculum. About 12% of the 368 total sites surveyed in Pennsylvania during this time contained small-footed bats, and exactly 12% of the 25 tunnels surveyed had small-footed bats present. The remaining three species of bats, the little brown bat (Myotis lucifugus), northern long-eared bat (Myotis septentrionalis) and the eastern pipistrelle (Pipistrellus subflavus) did not seem to like tunnels as well as other available sites. Indiana bats (Myotis sodalis), although present in two tunnels in the 1930's, have not been recorded in a tunnel since our surveys began in 1986. Surprisingly, analysis shows that the length of a tunnel is only mildly correlated with the size of the bat population within.

The next step in this research should be to determine the answer to some of the remaining questions. For example, why do two of the tunnels attract large numbers of little brown bats while the others do not? What makes tunnels a preferred site for big brown bats to hibernate? Can we manage these tunnels to encourage an increase in bat populations? Hopefully, within the next few years we will have the answers to these questions and will have an active management plan for conserving the populations of hibernating bats in Pennsylvania's tunnels.

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