Behavioural responses to barking and other auditory stimuli during night-time sleeping and waking in the domestic dog ( Canis familiaris)

Abstract

Urban dogs have previously been shown to have approximately 3 sleep/wake cycles per hour during the night. In this study the sensitivity of dogs to night-time stimuli at different stages of these sleep/wake cycles was tested. Twelve dogs were filmed at night in their usual urban habitats, whilst alert, in quiet sleep and in active sleep. In each state they were given six pre-recorded auditory stimuli of the same intensity, namely two barking stimuli (a single bark and repeated barking), two stimuli of concern to owners (rowdy young people discussing burglurizing, and breaking glass) and two other stimuli of common urban sounds (a motor cycle and a bus). When responses during quiet and active sleep were treated as a single group, dogs were found to be significantly more responsive to auditory stimuli when alert than when asleep, which was to be expected ( χ 2, P<0.005). However, there were no significant differences between the responses when the dogs were in quiet and in active sleep. This is unlike the situation in humans who are more responsive to auditory stimuli during rapid eye movement than during non-rapid eye movement sleep. Dogs barked on 29% of occasions in response to the 180 auditory stimuli. Dogs were more likely to bark or become more alert in response to barking than to other auditory stimuli ( P<0.001). Individual dogs which lived in groups were more likely to bark than were single dogs ( P<0.001). Within such groups, one particular dog barked consistently more than its companion(s) ( P<0.001). Dogs apparently perceived the significance of auditory stimuli, even in active sleep, because in that state they responded more to alarm-barking than to the stimuli of concern to owners. They did not bark at all stimuli and responded most to the sounds of other dogs.