<span style="font-size:11.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-bidi-font-family: Mangal;mso-font-kerning:18.0pt;mso-ansi-language:EN-GB;mso-fareast-language: EN-US;mso-bidi-language:HI" lang="EN-GB">Effects of light intensity on circadian activity behaviour in the Indian weaverbird (<i style="mso-bidi-font-style:normal">Ploceus</i> <i style="mso-bidi-font-style:normal">philippinus</i>)</span>

Abstract

Circadian (locomotor activity/perching) behaviour of the weaverbird <span style="color:black;mso-font-kerning:18.0pt;mso-bidi-font-weight:bold">(<i style="mso-bidi-font-style:normal">Ploceus</i> <i style="mso-bidi-font-style: normal">philippinus</i>) under different light intensities was studied. Six groups of birds were subjected to 12L:12D (L = 1000 and 10 lux and D = 0.3 lux) for two weeks, and thereafter released into constant dim illumination (LL_dim = 0.3 lux). After two weeks of LL_dim, birds were given a 2 h light pulse of 1000 lux at circadian time (CT) 12, 17 and 20, and exposure of LL_dim was continued for another two weeks and the activity pattern was monitored. As expected, all birds were entrained under 12L:12D showing dense-activity in the group that was placed under light phase of 1000 lux. Under LL_dim 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.<span style="color:black;mso-font-kerning:18.0pt;mso-bidi-font-weight: bold">

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