Date: October 5, 2016
Source: Virginia Tech
To
surprise their prey, some species of seabirds dive into the water at speeds
greater than 50 miles per hour. A human diver entering the water that fast
would likely sustain serious injuries, but birds, such as gannets and boobies, pull
off these dives safely in spite of their slender necks.
New
research from Virginia Tech helps explain how the birds manage these high-speed
dives.
"We
were interested in what happens when objects plunge into water, so we looked
for examples in nature; the gannets are incredible," said Sunny Jung, an
associate professor of biomedical engineering and mechanics in the College of
Engineering and an expert in fluid biomechanics; he has also studied dogs'
unusual drinking technique and how shrimp use microscopic bubbles to hunt.
In a
new study published in the Proceedings
of the National Academy of Sciences,
Jung and his coworkers investigate the biomechanics of gannets' dives. They
found that the birds' head shape, neck length and musculature, and diving speeds
work in concert to ensure that the force of the water doesn't buckle their slim
necks.
Previous
studies of the diving birds have focused on ecological aspects of this hunting
behavior, called "plunge diving." Jung's is the first paper to
explore the underlying physics and biomechanical engineering that allow the
birds to plunge beneath the water without injury.
To
analyze the bird's body shape and neck musculature, the team used a salvaged
gannet provided by the North Carolina Museum of Natural Sciences. They also
created 3-D printed replicas of gannet skulls from the collection at the
Smithsonian Institution, which helped them measure the forces on the skull as
it enters the water.
The
primary force acting on the gannet's head as it plunges beneath the water is
drag, which increases with speed. To analyze what other parameters affect the
force the bird experiences, the researchers created a simplified model from a
3-D printed cone on a flexible rubber "neck," and plunged this system
into a basin of water, varying the cone angle, neck length, and impact speed.
High-speed video showed whether the neck buckled.
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