Anthropogenic night light affects the muscle histology of redheaded bunting (Emberiza bruniceps)

Artificial light at night (LAN) often disrupts the nocturnal behaviors and physiological responses of migratory birds. En route to their migratory journeys, birds come across adversities pertaining to weather, food scarcity, temperature, and several anthropogenic factors. Among these factors, exposure to LAN has garnered much attention in the past decade. Artificial manipulation of daylength is known to cause differential effects on the behavior and physiology of photoperiodic organisms. To test the effect of exposure to different colors of light at night on the histomorphometry of the pectoral and cardiac muscle of birds, we subjected photosensitive redheaded buntings to all LAN (Light at Night) or No LAN treatments under 10L:14D photoperiod for 10 days. All LAN (~5 Lux) treatments comprised two groups having white and blue light at night, namely WLAN and BLAN, respectively. While the group having dark night i.e., 0 Lux at night was named the NLAN group. The daytime illumination with white light was set at 200 Lux. Food and water were ad-libitum in all the groups. We found that the pectoral muscle fiber and cardiac muscle fiber width increased under the LAN exposure, but the white and blue color of night light equally affected the muscle morphometry. However, the lipid accumulation in the cardiac muscle fiber showed the differential effect of colored light at night in which the WLAN group showed the highest lipid accumulation. We did not find any significant difference in the density of muscle fiber comprising the fascicle. So, these results suggest that the redheaded bunting showed a differential response to different colored LANs with respect to muscle fiber thickness and lipid accumulation in muscle fibers.