Replicas of gannet skulls from the collection at the Smithsonian Institution allowed researchers to measure the forces a bird’s skill experiences during a dive. (Photo by Sunny Jung/Virginia Tech)

The title may seem silly, but I can’t help that a whole family of birds are alternatingly called boobies or gannets – most of us have heard of the Blue-footed Booby, but there are several other species, all of which hunt for fish by diving, head first, at extremely high speeds from many meters above the water. For a human entering water at fifty miles an hour, a neck injury would be a certainty, and even organ damage could occur, but boobies/gannets accomplish the dives plenty of times during a day’s hunting, with no apparent problem. It seems that their physiology, as well as the way they contract their muscles during the plunge, save them from harm. From the Smithsonian Insider:

New research from Virginia Tech, the Smithsonian’s National Museum of Natural History, the National Museum of Rio de Janeiro and the North Carolina Museum of Natural Sciences 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, Smithsonian ornithologists Lorian Straker and Carla Dove and their co-authors 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’s National Museum of Natural History, 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.

Their analysis revealed that the transition from stability to buckling depends on the geometry of the head, the material properties of the neck, and the impact speed; at typical gannet diving speeds, the birds’ narrow, pointed beak and neck length kept the drag force in a safe range.

“What we found is that the gannet has a certain head shape, which reduces the drag compared to other birds in the same family,” Jung said.

The researchers also discovered that the birds further reduce the risk of buckling by contracting their neck muscles before impact, straightening the S-shaped neck.

The team is already extending their work to other species.

“One implication of this study is safety criteria for human divers,” Jung said.

Read the rest of the original article here.