Light at night reduces digestive efficiency of developing birds: an experiment with king quail

Artificial light at night (ALAN) exposes animals to a novel environmental stimulus, one that is generally thought to be maladaptive. ALAN-related health problems have received little attention in non-model species, and we generally know little about the nutritional-physiological impacts of ALAN, especially in young animals. Here, we use a novel application of the acid steatocrit method to experimentally assess changes in digestive efficiency of growing king quail (Excalfactoria chinensis) in response to ALAN. Two weeks after hatching, quail were split into two groups (n = 20-21 per group): overnight-light-treated vs. overnight-dark-treated. When the chicks were 3 weeks old, the experimental group was exposed to weak blue light (ca. 0.3 lux) throughout the entire night for 6 consecutive weeks, until all the chicks had achieved sexual maturation. Fecal samples for assessing digestive efficiency were collected every week. We found that digestive efficiency of quail was reduced by ALAN at two time points from weeks 4 to 9 after hatching (quail reach adulthood by week 9). The negative effect of ALAN on digestion coincided with the period of fastest skeletal growth, which suggests that ALAN may reduce digestive efficiency when energetic demands of growth are at their highest. Interestingly, growth rate was not influenced by ALAN. This suggests that either the negative physiological impacts of ALAN may be concealed when food is provided ad libitum, the observed changes in digestive efficiency were too small to affect growth or condition, or that ALAN-exposed birds had reduced energy expenditure. Our results illustrate that the health impacts of ALAN on wild animals should not be restricted to traditional markers like body mass or growth rate, but instead on a wide array of integrated physiological traits.