Effects of light intensity on circadian activity behaviour in the Indian weaverbird (Ploceus philippinus).

ABSTRACT

Circadian (locomotor activity/perching) behaviour of the weaverbird (Ploceus philippinus) under different light intensities was studied. Six groups of birds were subjected to 12L12D (L = 1000 and 10 lux and D = 0.3 lux) for two weeks, and thereafter released into constant dim illumination (LLdim = 0.3 lux). After two weeks of LLdim, birds were given a 2 h light pulse of 1000 lux at circadian time (CT) 12, 17 and 20, and exposure of LLdim was continued for another two weeks and the activity pattern was monitored. As expected, all birds were entrained under 12L12D showing dense-activity in the group that was placed under light phase of 1000 lux. Under LLdim birds exhibited circadian activity rhythms with periods longer or shorter than 24 h. Light pulse at CT 12 caused small delay shift in the activity phase, but a larger delay in phase shift occurred when the pulse was given at CT 17. A pulse at CT 20 caused small advanced phase shift. Thus, photoperiodic weaverbird appears to show circadian system regulated behaviour as seen by activity-rest pattern under programmed light cycles.