A team of researchers aims to find out what lemurs do all night while the rest of us are snoozing. In today’s post, Lemur Center volunteer and student researcher Joel Bray reports on what happens at the Center after the sun goes down, and what his team hopes to learn about the secrets of sleep:

Two fat-tailed dwarf lemurs peer from their perch in the nocturnal building.

With sunset long past, the Duke Lemur Center is dark and still, a spooky silence to which I’m unaccustomed. For the past four years, I’ve done noninvasive research with lemurs to reveal how they think. But with graduation behind me, I’ve started working with Dr. Charlie Nunn, a new professor in the Department of Evolutionary Anthropology at Duke. And we’re studying sleep, hence my presence here at night.

Lemurs exhibit a great diversity of activity patterns. Some are active during the day (diurnal), some at night (nocturnal), and others show a hybrid pattern (cathemeral) where they are active both day and night. Cathemeral lemurs even show variation in activity across seasons, depending on the weather and food availability.

Through noninvasive methods, we hope to explore the causes and consequences of this variation. For example, are there differences in the timing and duration of sleep/wake cycles? How is sleep quality influenced by sociality, light, and noise? Of particular interest to me, how does sleep quality influence cognitive performance? In the current phase of the project, we are working with about a dozen species here at the Lemur Center. Eventually, we plan to study wild lemurs in Madagascar.

But for now, the real fun is in being with the lemurs at night. We make periodic visits to survey the lemurs and learn what they are up to after the staff leaves. Do they prefer to sleep near group-mates or alone? Do they prefer to sleep on beams, platforms, or in baskets? These seemingly small factors are critical as we make decisions about the design of the project, especially because the answers vary widely between species.

After the sun goes down, we arrive with just red lights and whispers, roaming the halls and peeking in on the lemurs. The sifakas, ring-tailed and ruffed lemurs – traditionally thought to be diurnal – raise their heads as we pass by but otherwise tend to ignore us. In contrast, the cathemeral species of the Eulemur genus perk up immediately and either approach us or socialize amongst themselves. Babies of all species are particularly active once disturbed. It would seem that parental insomnia is not unique to humans.

We’ve recently started to collect pilot data from nocturnal lemurs with piezoelectric film. The material lies beneath the lemurs while they sleep in a nest box or custom-made “Mouse House” and records mechanical stress, allowing us to detect respiratory rate. We’ve also begun to place actigraphy monitors on the collars of larger-bodied species, from which we can acquire a record of animal movement. We’re exploring video amplification technology as well. Slowly, we’re shedding light on the many secrets of lemurs.

When we leave for the night, we pass by the only aye-aye that’s outdoors and on a natural light cycle. Out of the darkness he appears: Norman Bates. Seeing his outline in the moonlight, I stand in awe. Our current animal protocol does not include the aye-aye, though. His secrets, for now, remain safe.




Joel Bray has volunteered and conducted research at the Duke Lemur Center since 2009. He received his Bachelors degree in Evolutionary Anthropology from Duke in 2013. When not prowling the Lemur Center after dark, he cheers on Duke basketball while impersonating a primate.