Studies in Nocturnal Ecology, III. Recording Apparatus and Further Analysis of Activity Rhythm

The first measurement of nocturnal activity by recording apparatus was by Johnson ('26). Relatively heavy animals were used, e.g., forest deer mice, which allowed a simple technique to be employed. This consisted in placing a mouse in a light-weight cage suspended by rubber bands. An indicator fastened to the cage traced the animal's movements on a record made by a paper disk turned by clock mechanism. Unfortunately the apparatus, though simple, was neither figured nor fully explained; neither was the temperature, which varied seven degrees, nor presumably the humidity, adequately controlled. The work was important, however, in that it recorded nocturnal activity, and gave an insight into the behavior of characteristic forest rodents. Quite recently Davis ('32, '33) has reported an improved apparatus of the same general type for recording the activity of small mammals. Turning from mammals to the insects, the only other group of animals in which nocturnal activity has been measured by recording apparatus, significant work has been done by Lutz ('32a, b) on three species of Orthoptera. Here the small weight of the animals necessitated a much more refined technique. This work is so recent that it is sufficient to mention the lprinciple used. The weight of an insect depressed a counter-balanced treadle, completing an electric circuit through an electromagnet, which in turn moved an inked pen which registered the animal's movements upon a moving drum. Unhappily such an excellent piece of equipment was neither described nor figured in the text, nor were the experimental conditions of the cellar, in which the experiments were conducted, fully described. The work, however, is the best that has been done with recording apparatus in measuring nocturnal activity. Four years ago the writer began construction of a recording apparatus' which would measure objectively the activity of small animals. The circular disk of a phonograph, having a diameter of eleven and three-quarter inches, or No. 10 aluminum pan-covers, were threaded at the exact center so that a brass screw, which was lathed to a blunt point, could be inserted from above and adjusted to any required length. This screw point was centered on a dish-shaped table made by cutting off the end of another brass screwv and