Diving is a lot of pressure for a bird. Take the Northern Gannet, which is often likened to a torpedo, as it plunges hundreds of feet to spear fish from the ocean, sometimes reaching 60 miles an hour.
Plummeting from sky into water is a huge force, “especially when you’re moving so fast,” says Sunghwan Jung, an assistant professor who studies fluid dynamics at Virginia Tech. He and a team of Virginia Tech engineers and staff from the Smithsonian Museum of Natural History including Carla J. Dove of the Division of Birds, were curious why humans get injured by high impact dives, but seabirds do not.
Since the scientists couldn’t catapult live birds into the ocean, they dropped dead and mock seabirds into a four-foot tank of water. Their study subjects included a dead gannet (a frozen specimen donated by the North Carolina Museum of Natural History) and 3D-printed seabird replicas.
After testing out the dead specimen, the team discovered that the highest probability of the gannet’s neck snapping came mid-dive—with the head fully submerged and the body still above water. “There is was a very strong compressive force on the bird’s neck at this point,” says Jung, who recently presented this research at the American Physical Society meeting.
When the team tried out their next subject, a 3D bird model, they saw that the longer the “neck” was, and the faster the “bird” fell, the more likely the neck was to buckle and break.
Jung thinks this could mean that birds have an ideal ratio between neck length, diving speed, and other factors that ensure survival during dives: “Evolution helps to choose the right speed,” he says.
The one element that Jung’s team could not account for is the form a live bird takes upon diving. “A gannet folds itself up into an arrow,” says Iain Stenhouse, the Marine Bird Program Director at the Biodiversity Research Institute. This streamlined shape allows the bird’s body to absorb some of the impact, taking a little pressure off the neck.
Jung’s team’s research is still preliminary, and they’re devising a final paper that Jung hopes to publish this summer.
Stenhouse says that gannets compensate for their long necks in many ways, including internal air bag-like structures and resilient skulls. There must be a maximum force that these birds can bear, he says, but they can dive from almost any height (very low to over 200 feet high)—we just can’t seem to find their limit.