How can scientists be so sure the years are so many? There are several ways in which they have been able to establish that the centuries have been numerous since the bats first discovered this haven.
One of the best is by the guano deposits found on the floor of the cave. Observations have shown that the excrement from the bats accumulates at the rate of approximately one-half inch per year. Thus 25 years is required for a foot of the substance to materialize. This would indicate it would require about 1,000 years for 40 feet to accumulate.
Unfortunately, the exact thickness or depth of the guano deposits was not carefully measured when my father first discovered them, but I have heard him describe them many times as being at least 100 feet deep in places. That would be almost conclusive proof that the bats had been living in the cave for at least 2,000 years!
It should also be remembered that as guano ages and dehydrates, it sort of packs down, so that although a half inch of guano might be deposited in a year's time, several years later this guano will have decayed and packed down to half that thickness.
This would extend the time to far more than the estimated 2,000 years, but just how much is extremely difficult to estimate.
Also, the amount of guano growth varies with the years, for when insects are plentiful, bats gorge themselves and the guano deposits are much greater than in lean years when their food supply is low, sometimes to the extent that the bats will go elsewhere for one or two seasons, at which times there is no guano accumulation at all.
At one time, during an exploration of the cave some years ago, a scientist discovered the remains of a bat sticking out of the side of a stalagmite where it had undoubtedly fallen from its perch above, having perchance died of old age.
With no disturbance to blow its remains away, it rotted there and the stalagmite grew over it, so to speak. Scientists, estimating the rate of growth of stalagmites, were able to calculate approximately how long ago the bat had fallen. The head and wing bones were barely discernable.
It is also known that the bats have moved around in the cave, for their tiny skeletons have been found in remote sections at points where the bats are no longer found clinging to the ceiling for their daytime sleep. Such findings indicate one of two possibilities; one, that some bats might have gotten lost in the cave and died there, away from their normal resting place, and, second, that previous openings have since been closed, due to various earth movements, forcing the bats to use new openings and thus change their location within the cave.
Scientists place little credence on the former possibility because bats seldom get lost. They can find their way in any dark cave or passageway and know how to get out the same way they went in.