HIBERNATION AMONG BATS

The hibernating habits of different species of bats differ so much that it is difficult to generalize. There is some evidence that some bats migrate upon the approach of winter, but most of them hibernate. Bats live on winged insects and must catch their prey in the air. Their feeding days are limited, except in the South, where insects fly about for a longer season. Indeed, their feeding days must be very short if frost comes early in Autumn. Their period of hibernation may be more than half a year. Their death-like inactivity is made necessary because of the need to make their meagre supply of stored food hold out over such a long period of time. In the long winters of the north, hibernation often means going without food for five, six and seven months. If bats are to survive, it is essential that their food resources be made to hold out as long as possible.

Bats cluster in masses, usually in caves, old barns, and other places that offer protection from the inclemencies of winter. The hibernating bat appears in all respects dead. Its temperature sinks very low, its heart beats so feebly it is barely perceptible, and it takes long to awaken from its sleep. One naturalist describes the "winter sleep" of bats in the following words: "Most bats when fallen into their winter sleep look dead as nearly as may be. They grow cold, their heart beats feebly, and when they hang themselves head downward on some dusty beam or crouch in some smouldering wood, they might be taken for lumps of leather. Nothing about them suggests a living creature, and no one would imagine for a moment that they would presently be flying with a dash and a skill and a command of quick turns beyond the power of a bird."

Griffin says of the hibernating bat, "the heart rate slows to a point where it cannot be detected. Breathing almost ceases. The blood moves sluggishly. The body temperature falls almost to that of the surroundings.

"Bats hibernating in a cave where the air temperature is 33° F. may have a body temperature of 33.5° F. They feel cold to handle, and are stiff and unresponsive. It requires close observation to distinguish a hibernating bat from a dead one."

There is evidence that bats may awaken spontaneously during the winter and fly around in their cave, even in rare instances, flying considerable distances to other caves. Griffin says that "they are not continuously dormant throughout the whole winter. On successive visits to the same cave we usually found the bats in different parts of the passages, even when they were not disturbed on the previous visit. Probably they wake up from time to time and fly about a bit, perhaps occasionally wandering out of the cave to see whether spring has come yet, and then hang themselves up again for another long sleep." "Flying from cave to cave in winter seems to be a rare occurrence, but we obtained three returns of banded bats which had flown 55 to 125 miles from one cave to another during a single winter."

Date: 2015-01-11; view: 767