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See Inside January 2011

Do Giraffes Float?

Two scientists and a computer weigh in on a long-standing mystery about giraffes



Courtesy of Donald Henderson and Darren Naish

If you dropped a giraffe into a deep pool of water, would it float, or would it sink? If it could float, would it swim briskly and confidently to the nearest bit of land, or would it flail around helplessly and drown?

Strange as it may seem, the floating and swimming abilities of giraffes—or rather their supposed lack of floating and swimming abilities—have often been written about by experts. It has been asserted that giraffes “sink like stones” and “cannot swim, even in an emergency,” and that “rivers are an impassable barrier to them.” Although a few rare photographs and segments of film show that giraffes will wade into deep rivers when they have to, definite observations of them swimming have yet to be reported.

One way to examine the behavior of giraffes in water would be to push one into a deep pool and observe the results. Ethical and practical concerns make this hypothetical experiment impossible, so I thought of another solution. Inspired by sheer curiosity, I approached Donald Henderson of the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta, who had created a three-dimensional computational model of a giraffe for another project and had also tested the buoyancy of assorted living and extinct animals by using flotation-simulating software. Could Henderson, I wondered, test the buoyancy of his “digital giraffe” in the same way? If he could, we might be able settle this question once and for all.

To compare the model’s aquatic behavior with that of other animals, we performed calculations to determine an immersed giraffe’s centers of mass and buoyancy, the resistance it encountered when moving its limbs, and the friction it encountered across its whole surface. We had to take account of the giraffe’s unusually shaped lungs, the size of which has been the subject of disagreement among experts. Having tweaked the model to make it as plausible as possible, we were ready to see whether the giraffe could float and swim. Our analysis and conclusion appear below:

  • The heavy forelimbs and shoulder region would pull the front half of the animal downward, thereby forcing the neck into a near-horizontal posture.
  • The giraffe’s relatively high density, particularly in its limb bones, would make it sit very low in the water, and it would suffer from high drag.
  • The animal would have to hold its head upward at an uncomfortable angle, and it would be unable to move its neck up and down in concert with its limb movements.

Conclusion
Giraffes can float, but they would be clumsy and unstable in the water.

Discussion
Testing the swimming abilities of a giraffe might seem like a frivolous exercise. But analyzing the question is of great interest to anyone engaged in the biology or management of the animals. Our study also showed that scientists could rely on computer simulations to help examine fascinating questions in biomechanics.

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