The Influence of Flicker Rate on Plasma Corticosterone Levels of European Starlings, Sturnus vulgaris

Recent reviews have highlighted the differences between human and avian vision with regard to temporal resolution and the potential problems it may cause for avian welfare and video playback experiments. Birds tend to have much higher critical fusion frequencies than do humans (>100 Hz vs 50–60 Hz in humans), which means that they perceive light as flickering up to and over 100 Hz. This is higher than most television monitors (which have refresh rates of 50 or 60 Hz) and normal fluorescent lighting (100 or 120 Hz), and because humans find flickering light aversive, it has been suggested that birds will as well. If this were the case, then there would be welfare implications of maintaining them under such lighting and also a potential effect on their behavioral responses in video playback experiments. However, there is some behavioral evidence that indicates that birds do not appear to find flicker aversive and may even prefer flickering lighting. The authors aimed to determine whether a passerine, the European starling, found flicker aversive by measuring the corticosterone stress response in birds maintained under high- or low-frequency fluorescent lighting (35–40 kHz vs 100 Hz) for 1 or 24 h. The results suggest that low-frequency lighting is potentially more stressful because, where differences exist, birds in the low-frequency treatment always showed higher basal corticosterone. However, the evidence is not consistent because in half of the blocks, there were no significant treatment effects and, where there were, the time course of the effects was variable.