How Does a Giraffe Stoop to Drink?
Because of its long legs and neck, drinking is a difficult chore for the giraffe. The neck of a giraffe has only seven neck bones (or vertebrae). Each vertebra, however, is very long. Because of this, a giraffe always has a stiff neck. In order to drink, it must spread its legs far apart or bend its front knees until it can reach the water.
When you watch a giraffe feed, you can see at once how it’s peculiar build enables it to get food. Because it is so tall, a giraffe is able to eat the tender leaves from tree-tops nearly 20 feet above the ground.
To drink water giraffe have to adopt a very ungainly position with legs widely spread as shown in the image. This places them in a position of extreme vulnerability to predators for it requires much effort and precious time to get into this position and regain an upright posture when they have finished drinking.
Giraffe seem to be aware of this because they are very circumspect before they actually commit themselves to taking up the drinking position and will stand for a long time at a waterhole carefully observing the surroundings before they will finally move to the water’s edge and drink.
How a giraffe, the tallest animal on earth, then propels that water up its long neck to reach its stomach has been a mystery. Now, new research suggests the secret may lie with a simple device known as a plunger pump.
Typically, a plunger pump uses one stroke to draw water or other fluids into a cavity through one valve and then another stroke to push the liquid out again through a second valve. Variations of the pump are common in wastewater treatment and the oil and gas industry.
But where do giraffes store their plunger pumps?
In the model proposed by the researchers, the giraffe’s lips form one valve of the “pump” while the animal’s epiglottis, located at the back of the mouth, is the other. To start, the giraffe sinks its puckered lips into the water and then pulls back its jaw, allowing water to rush into the mouth while keeping the epiglottis “valve” closed. Next, the giraffe clenches its lips, relaxes the epiglottis, and pumps its jaw so that the captured water is pushed into the esophagus.
The cycle repeats, moving more and more water into the esophagus. At some point, the giraffe lifts its neck, and the water sluices into its stomach, thanks to gravity and the wave-like muscular contractions known as peristalsis.
The researchers estimate that the giraffe pumps water in at a speed of about 6.7 mph — fast enough to overcome the pressure from the water that’s already stored in the esophagus and preventing it from rushing back out.
Based on the dimensions of a giraffe esophagus, the researchers estimated that a full one can hold about 1.3 gallons. Additional calculations revealed that each pump probably sends about 10 ounces of water into the throat and that a long drinking episode of about 25 seconds could involve up to 17 pumping cycles.