(Margaret Voss, Syracuse University, Caren Cooper, Cornell University)
Artificial light at night is increasing as urbanization spreads worldwide. There is increasing evidence that ecological disruptions, such as increased light exposure, might alter the natural environment enough to induce evolutionary changes in some organisms. Behavioral responses to anthropogenic stimuli may result in either a rapid population increase if it improves a species’ fitness or its decline if maladaptive traits are selected for. Based on past lab studies where animals gained excessive weight as a result of extreme light exposure, circadian rhythm disruption is correlated with behavioral responses to light at night. The hormones melatonin and cortisol are the drivers of this biological process. Melatonin, which controls our sleep cycles through light detection, will remain suppressed throughout the day and rise at night while cortisol is active by day and helps regulate glucose metabolism.
Melatonin is also known to regulate body mass, digestive efficiency and metabolic rate. Therefore any negative effects from excessive light exposure should be seen at a physiologic and metabolic level within an organism. In birds, glucose levels are normally elevated to accommodate the need for readily available energy for flight. The avian nervous system also requires higher levels of circulating glucose than other vertebrates. To better understand the implications of light at night on avian stress responses, barn swallow chicks were kept under a 24-hour light exposure and compared with a control group kept under ambient natural light. We followed chick’s hourly growth rate for the first three days after hatch and daily growth rate until they fledged. We compared weights (g), the ratio of the length of the head (mm) to the bill (mm), tarsus length (mm), and wingchord (mm), as well as blood glucose levels (mg/dL) to assess differences between the treatment and the control groups. The results suggest that prolonged exposure to artificial lighting may disrupt circadian rhythms in birds and lead to negative health consequences.