A behavioural study of sleep patterns in the malachite sunbird, Cape white-eye and fan-tailed widowbird

The function of sleep in birds is poorly understood, even though birds spend a large part of their lives sleeping. Sleep behaviour in passerine birds has not been looked at as extensively as that of nonpasserine birds. We looked at the sleep behaviour of three passerine birds occurring in southern Africa, namely the malachite sunbird, Nectarinia famosa, the Cape white-eye, Zosterops virens, and the fan-tailed widowbird, Euplectes axillaris. By using an infrared-sensitive camera, we recorded basic sleep behaviour, at various ambient temperatures, of all three species, such as sleep position and eye closure. We also investigated the incidence, or lack thereof, of unihemispheric sleep. Individuals of all three species spent most of the night asleep and woke up intermittently throughout the night, with no significant differences between temperatures. Cape white-eyes and malachite sunbirds showed an increase in back sleep and a decrease in front sleep at 5 °C. Little evidence of unihemispheric sleep was found, suggesting that it is more likely to occur in nonpasserines.