Anthropogenic stressors, such as artificial light at night (ALAN), increasingly affect the sleep behaviour and physiology of wild birds, particularly in areas where human activity is prevalent. To understand the consequences of the resulting sleep deprivation, it is essential to investigate whether the effects of sleep deprivation on cognitive performance, observed in humans, also occur in birds. Here, we studied the impact of sleep deprivation, induced by intermittent exposure to ALAN, on inhibitory control, vigilance behaviour, and exploratory behaviour in great tits. Furthermore, we hypothesised that the effect of ALAN could depend on an individual's natural sleep duration and the timing of sleep. To achieve these goals, we measured emergence and entry times from/into the nest box in the wild, before capturing the great tits. In captivity, half of the birds were exposed to intermittent ALAN, and cognitive performance was assessed the following morning for all birds. ALAN-exposed birds were less successful on the detour reach task and when they started pecking at the test tube, they pecked more often. However, neither of the effects was related to the natural sleep duration or timing, in contrast to our hypothesis, and there were no differences between the ALAN-exposed and non-exposed group in vigilance and exploratory behaviour. Thus, even one night of exposure to ALAN can negatively affect cognitive performance in wild birds, possibly with negative effects on their performance and survival.
