Abstract
In a former communication 1 to this society it was shown that the absence of food is an important factor in determining the onset of hibernation in the woodchuck (Marmotta monax). In the present note attention is drawn to the fact that the cause of the awakening of these animals from their torpid condition in the early spring is not a rise in the temperature of their surroundings.
A colony of woodchucks was kept in artificial burrows a little over four feet 2 below the surface of the ground, as already described. 3 At the bottom of one of these burrows, the oil bulb of a Friez thermograph was placed, and connected with the recording clockdrum contained in a box at the top. All the burrows were packed with dry straw, while the one containing the bulb was shut off from the central court, to prevent the woodchucks having access to it.
A continuous record of the temperature at this depth has been kept from January 1, 1912, till the present time. It shows that the lowest temperature is reached late in March or early in April— just about the time when the hibernating woodchucks are beginning to wake up. There is no appreciable rise in temperature till well on in April.
The diurnal variation, so marked at the surface, is almost completely abolished at this level, all the year round, and this is a circumstance which greatly favors animals with an imperfectly developed heat regulating mechanism, such as the woodchuck possesses.
Records of the air temperature taken at the Ithaca station of the U. S. Weather Bureau, situated about half a mile from the burrows, show that in 1912 the coldest month of the year was January, and in 1913, February, the average mean temperatures for the first four months being as follows:
Notwithstanding the fact that the weather in these four months was much milder in 1913 than in 1912, the temperature at the depth of four feet, in March and April 1913, as indicated by the thermograph, was about 2° F. lower than in the corresponding months of 1912. The snowfall, however, was greater in 1912 than in I913 and this will probably explain the apparent anomaly.
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