Photoperiodic response of a subtropical Passerine, the red-vented bulbul, Pycnonotus cafer stanfordi Deignan

Abstract

: In the present study, photoperiodic response of red-vented bulbuls, Pycnonotus cafer stanfordi Deignan was studied at Lumami (26oN), Zunheboti district, Nagaland. In birds kept under natural lighting, testicular and follicular developments began in February (daylength 11.5 hr/day); gonads developed progressively through March-May period (12-13 hrs/day), peaked in June (13hr, 34min/day) and thereafter declined to reach smaller in size during September. Seasonal changes in the size and activity of gonads were abolished in birds transferred to fixed duration of 10L/14D during December (quiescent phase). Under constant 16L/8D and 20L/4D photoperiods, gonads developed almost at similar pace, peaked in 3 months of exposure and thereafter, regressed fully during next 3 months owing probably to the development of photorefractoriness. Absolute development of gonads was not significantly different in groups kept under natural lighting (13hr, 34min/day), 16L/ 8D and 20L/4D daylengths. Body mass cycles of birds kept under NDL, 16L/8D and 20L/4D were temporally similar to gonadal cycles. No significant change occurred in the body mass of birds exposed to constant 10L/14D. It may be suggested that some common mechanisms engender photoinduced changes in gonad and body mass of red-vented bulbuls and daylengths higher than what birds experience naturally are superfluous in impacting the neuroendocrine and metabolic mechanisms.