Gentle giants

Giraffes are the tallest terrestrial vertebrates (males stand about 20 feet tall, females slightly less), which opens up leafy resources other browsers like the stately kudus lack, but also present a host of problems for survival.

Giraffe feeding on high vegetation

Stretching to reach those last few leaves on the acacia tree–food is scarce in the dry season in Botswana.

That long neck that makes up 50% of their height makes it a challenge to pump blood against gravity up to the brain.  Consequently, their highly muscular, thick-walled heart has to generate more than twice as much pressure as the human heart does. (Giraffe blood pressure runs about 280/180–normal human blood pressure is about 120/80 or lower).  That’s fine for getting blood to the brain, but blood flow is all downhill to the feet, so how do giraffes keep from getting swollen ankles?  With tight-fitting, elastic skin that acts like compression stockings, the kind they give heart patients to wear.

Giraffe in Botswana

The tallest object in this environment, but just look at those skinny little legs that support the massive upper body mass.

Their height also gives them a bird’s eye view of their surroundings, including predators perhaps lying in wait in the grasses below, but that same height advantage becomes a disadvantage when giraffes need to awkwardly bend over for a drink or food on the ground.

Giraffes feeding on a carcass in Botswana

Two giraffes were taking turns getting a bite of a decaying carcass. They eat bones and cartilage left by scavengers to obtain minerals lacking in their leafy diet.  The giraffe on the right has spread its front legs wide to enable its head to reach the ground.

Just getting into position for a drink or a bite of something on the ground is a mechanical problem in itself.  But lowering its head below the level of the heart poses a great risk of cerebral hemorrhage.  To combat this potential physiological disaster, arterial pressure sensors detect changes in head position and cause an immediate decrease in heart rate and heart contraction strength to decrease blood pressure.

Great vertical height poses problems for other organ systems as well.

Male giraffe feeding on acacia

Giraffes are ruminants, and like cattle, they regurgitate what they have browsed to re-chew it into smaller pieces.  That requires a long, very muscular esophagus, capable of returning food from the stomach to the mouth.

Very long necks require very long nerves running from the brain to the periphery.  For example the nerve that stimulates the vocal cords and muscles that enable swallowing is 5-6 feet long!  It better conduct very fast, or food will go down the wrong tube (i.e., the trachea) when they swallow.

Giraffes love to browse on acacia leaves, but the plants have a great plenty of protective thorns, which the giraffes’s almost prehensile lips and tongue seem adept at working around.

Female giraffe, showing tufts of hair on the horns

That soft upper lip is highly mobile. Inside the mouth is a 20 inch long, highly muscular tongue that can delicately wrap itself around tiny leaves but avoid prickly thorns.  And just look at those long eyelashes, and big brown eyes.  Isn’t she a beauty?  (Hairy tufts at the end of her knobby horns indicate this is a female).

With their graceful walking stride and elevated height, giraffes just epitomize the “gentle giant” title.

6 thoughts on “Gentle giants

  1. Like most people I have been familiar with giraffes since childhood but I never thought of the problems their shape could present. I’ll never look at another giraffe in quite the same way. Amelia

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