A Night in the Life of a Giraffe
How Giraffes Sleep to Escape Predation
Background
Energy use is the master key that unlocks the reasoning behind everything an animal does. If an animal is foraging for food, they must save a bit of energy to harvest the food once they find it. In the same way, if animal decides not to forage for food, they will begin to lose energy. However, animals must also sleep, which can pose a deadly predicament. To giraffes, who must be concerned about predators, they must also produce effective defense mechanisms to avoid predators. Like humans, giraffes are suspected to enter a REM sleep cycle every night, during which they are susceptible to predation. The nocturnal life of a giraffe consists of balancing vigilance (or attentiveness to their surroundings), eating, and sleeping.
Giraffes are listed as vulnerable by the ICUN and their population numbers continue to decline. Any information about giraffe habits, especially during a time of night when they are most prone to mortality, is important to the species’ survival!
Summary: Long-Legged Lookouts
Scientists discovered that giraffes gather in groups of up to twelve at night, with at least one giraffe remaining awake at all times. The “lookout” giraffe constantly watches for danger. This watch post would cycle to different members of the group, as giraffes must continue to eat throughout the night to replenish energy spent on sleeping. No more than three giraffes would sleep at a time, with the oldest staying on the outskirts of the group. A giraffe was classified as in a REM sleep cycle when their neck was tucked over their back in an unguarded, relaxed fashion.
The scientists recorded a total of 152 REM sleep posture (RSP) events for 50 giraffes.
To observe the giraffes at night, the scientists attached four thermal imaging cameras to a mini iPad mounted onto a tripod. It is difficult to collect video data in the dark, which is why they had to track the heat imprint of the giraffes. The scientists also had to stake out their study from a car so that enough distance would be between them and the giraffes to prevent disturbing the animals or skewing data. This made it difficult (and sometimes impossible) to follow the giraffes when they decided to move, which was every 3–5 hours. To confirm data, the scientists would observe imprints left in the grasses once morning came.
The scientists noted that the giraffes slept less in Namibia’s wet season than the dry season, with 73 RSP (shorter periods) recorded in the wet season and 79 (longer periods) in the dry. They speculate that because of increased vegetation during the wet season, the predators have more cover, and the safe resting areas are scarcer. Typically, the giraffes chose to rest in more open sites with fewer trees, or plant flora that grew close to the ground, which gives them a more cohesive view of their surroundings.
The giraffes are also more likely to remain active during the rainy season nights because of the ample food sources. When there are more plants, it is worth the energy to forgo sleep and eat.
The natural predator of giraffes is the lion, and although this particular study was done at a game reserve in Namibia that prevented giraffe-lion interactions, it is possible that coevolution is involved in giraffe anti-predator sleeping behaviors. With male lions hunting in dense undergrowth and female lions more likely to hunt in the open, the giraffes have shown an innate preference towards more open areas. However, their sleeping behavior might be altered in the presence of a real threat, unlike in this study.
The more humans are active during the day, the more mammals tend to increase otherwise abnormal nocturnal activity. With this said, whenever the sun began to set, scientists observed giraffes beginning their choppy sleep routine. The scientists emphasized the importance in defining the giraffe’s nocturnal behaviors. It is essential to understand what conservation actions to take so giraffes may continue surviving, especially as their habitats continue to fragment and decline alongside human population growth.
