The stability of the circadian rhythm of green finches (Carduelis chloris) under the influence of a weak electrical field.

Free-running activity rhythms of nine green finches (Carduelis chloris) were studied under the influence of a 10-Hz square-wave electrical field. With a field strength of magnitude of E = 2.5 V/m in the empty cage, the population had a mean period of 23.64 +/- 0.77 hr. In the same experiment, but without the electrical field, the period was 23.66 +/- 0.80 hr. These results are in contradiction to Wever's description of a field-induced shortening of the period. A series of experiments with 10-Hz pulses of the same square-wave form, yet with various field strengths (8.7 and 65.2 V/m), also gave no effects.