A Sleepover At The Zoo: The Best Bits

The BBC teamed up with Bristol Zoo to rig the zoo with cameras in a first of its kind experiment to find out what their residents get up to at night. Presented by Liz Bonnin with the help of animal sleep expert Bryson Voirin the show gives us an exciting, never before seen insight into the sleep behaviours of a wide range of wild animals. We’ve picked out some of our favourite bits from the show… For many animal behaviour experts “there are a few gaps in our knowledge, and one of the greatest mysteries has been the nature and function of sleep.” says Liz as she introduces the show. This is the first experiment of its kind using night vision cameras and motion sensors to track the movements and behaviour of animals during the night. After setting up the cameras and reels and reels of cables the team set up their headquarters in the zoo theatre. A panel of lights at the HQ signal when the motion sensors have been triggered. A green light means the animal in that enclosure is moving and a red light means they haven’t moved “for 30 seconds or so”. Unfortunately the Pygmy Hippos are not a part of the study as Serana the hippo didn’t adjust to the camera being in her cage and hid for three days. It’s essential to give the subjects time to get accustomed to the intrusion so as not to interrupt the experiment. A part from Serana the camera shy hippo the other animals were initially curious but quickly adjusted. One silver back gorilla recognises cameras and is upset by them so they had to use cameras already installed in the gorilla house to record their nocturnal movements.

Gorillas are among the first animals to fall asleep, particularly one female gorilla cuddling her baby just after she collects wood chippings from the floor to build a nest for the night. She builds a new, fresh nest every night. It takes mother and baby just 30 minutes to settle down to sleep. The gorillas begin preparing for sleep as soon as the sun sets. This programme looks at some of the causes of sleep – light changes, internal body clock and the urgency of our brains needing sleep.

For many animals in the zoo they sleep not only when they need to but when it is safe to sleep, a natural survival instinct. Ants use ‘doormen’ to stop certain ants from entering the nest and disturbing the other ants who are being in-active or what we would call sleeping. Their society is structured in a way so as to maximise the amount of individuals who can experience inactivity at a given time. This structure to preserve a sleep-like behaviour for the good of their society is similar to how flamingos behave. Flamingos cluster together at night with individuals of the flock keeping vigilant for predators to protect the rest of the flock. The difference between the two is that ants have assigned sentries whereas flamingos share sentry duty between individuals of the flock. Liz and the team conducted an experiment to test the alertness of meerkats whilst they are sleeping. The group of meerkats – called a Mob – sleep piled on top of one another in a nesting box. A night vision camera was placed in the box to monitor the Mob’s responses as different sounds were played to test how alert they are. They used wind sounds and meerkat alarm noises at different volumes and these were the results… The sound of wind, even at the highest volume showed no response from the mob, but the meerkat alert noise (the noise meerkats make when a predator is near) at a medium volume and above provoked a response. Each time one member of the Mob left the nest box to poke its head outside and look for predators. Once satisfied there was no danger the meerkat returned to the nest box and snuggled back in.

Dolphins’ sleep patterns are particularly interesting as they do something called unihemispheric sleep which is where one half of the brain can sleep while the other half stays awake enough to breathe and swim. They do this by closing one eye which ‘switches off’ the corresponding brain hemisphere. Bihemispheric sleep (both brain halves sleeping together) may have been caught on camera as they film one dolphin resting at the surface of the water to breathe then it drift down towards the bottom and wakes just before it hits the bottom. This is the first time a sign of bihemispheric sleep has been observed in dolphins.

Sleep Terminology

Cathemeral “cat naps” – sleep during day and night in intervals e.g. lions

Nocturnal – sleep during the day e.g. red pandas

Diurnal – sleep at night e.g. Flamingos

Monophasic – sleep in one go

Polyphasic – sleep in short phases