Some lemurs are active during the day and sleep at night, like adult humans. Others are active night and day, like human teenagers, and sleep in irregular bursts. David Samson at the University of Toronto in Mississauga, Canada, and his colleagues wanted to know whether lemurs that sleep mostly at night — keeping what is known as a ‘diurnal’ schedule — would be more affected by sleep loss than their more flexible ‘cathemeral’ cousins.

In the first protocol, the team woke some lemurs every 15 minutes over the course of 4 hours by playing recordings of noisy events such as storms and falling food dishes. Other lemurs were left in peace. In a second session, some lemurs were subjected to the noises every five minutes for ten hours. The researchers then tested the primates’ recall and other skills.

Long-term memory suffered in all of the lemurs after nights of terrible sleep, supporting the hypothesis that primates consolidate memories while snoozing. The strictly diurnal lemurs in the genus Propithecus saw the steepest decline in their foraging efficiency, hinting that the cathemeral lemurs — such as the ring-tailed lemur (Lemur catta) — are better able to handle sleep disruption.