Anthropogenic noise is an ubiquitous disturbance factor, which, owing to the extensive nature of transportation networks, and ability of sound waves to penetrate distances, has wide-reaching impacts on biological communities.  Research effort on biological effects of anthropogenic noise is extensive, but has focused on waking behavior, and to our knowledge, no published experimental study exists on how noise affects sleep in free-living animals.  Sleep plays vital functions in processes such as cellular repair and memory consolidation.  Thus, understanding the potential for noise to disrupt sleep is a critical research objective.  Whether different noise regimes exert distinct effects on behavior also remains poorly understood, as does intraspecific variation in noise sensitivity.  To address these knowledge gaps, we used a repeated-measures field experiment involving broad-casting traffic noise recordings at great tit (Parus major) nest boxes over a series of consecutive nights.  We evaluated whether increasing the temporal variability and amplitude of traffic noise increased deleterious effects on sleep behavior in free-living great tits, and whether individuals differed in the magnitude of responses.  We found that traffic noise reduced sleep duration, proportion, and bout length, and induced birds to exit nest boxes earlier in the morning.  There was some support for a stronger effect of more variable noise, and relative to lower amplitude noise, higher amplitude noise resulted in less and more fragmented sleep.  Effects of noise on sleep duration were stronger in older adults, and substantial, repeatable variation existed in individual responses. We demonstrate for the first time that anthropogenic noise can have strong effects on sleep in free-living animals, which may have cascading effects on waking behavior, physiology and fitness.  Results suggest that reducing the amplitude of traffic noise may be an effective mitigation strategy, and that differences in individual sensitivity are important to consider when evaluating effects of noise exposure.  

The effect of anthropogenic noise on the sleep behavior of free-living great tits (Parus major) was assessed using infrared cameras installed inside nest boxes.  A repeated-measures experimental design was used in which sleep behavior was first recorded in the absence of noise on the first night (baseline).  The following two nights sleep behavior was recorded in the presence of either temporally consistent or variable traffic noise, with the order of the presentations determined in a semi-balanced random fashion.    

ES1= exploration score as measured the first time the bird was ever tested.  The sleep behaviors assessed were sleep duration (SleepDuration), sleep proportion (SleepProp), sleep bout frequency (number of sleep bouts/hr; SboutFreq), sleep bout length (hrs).