A University of Washington study published Oct. 12 in the Anatomical Record reports that gannets and boobies survive plunge-dives because their neck vertebrae are stockier than other birds’ and carry an extra contact surface that stabilizes the cervical column. The birds hit the water at about 70 miles per hour.
A northern gannet spots a fish school from 100 feet up, pitches into a nosedive and breaks the surface at 70 miles per hour. Its neck stays intact.
CT Scans Show Gannet and Booby Necks Built Thicker
The researchers began studying the mechanics of plunge-diving years ago. Gannets are built to withstand immense pressure on the head and neck, which compresses the cervical column. The link between beak shape and foraging behavior is well documented, but the connection between neck structure and feeding has received less attention.
“We see that the birds that plunge-dive have more robust vertebrae. They’re thicker, wider, and also shorter, shaped more like a square.”
Megan Vanderberg, lead author
In gannets and boobies, the second through sixth vertebrae also have an additional contact surface, called an articular facet. Researchers think it keeps the neck from bending backward when the bird strikes the water at an angle, so the load passes down the column instead.
Why a Long, Slender Neck Survives Impact
Engineers usually favor short, fat structures for compressive loads, the study’s account notes, yet gannet necks are long and slender, with 15 stacked vertebrae in a gentle s-curve. Earlier work had shown that surrounding muscles lock the vertebrae in place before impact, but few studies had examined the bones themselves. Senior author Bart Boom, a postdoctoral scholar at the UW’s Friday Harbor Labs, said the aim was to figure out what makes gannets so special
.
Kingfishers Have Blocky Bones but No Extra Facet
Kingfishers belong to a different avian family and are much smaller. The researchers still found blocklike vertebrae in them, but no extra facet. Their necks appear to have evolved in a similar way.
Scaling also matched. Larger necks had larger vertebrae, and kingfishers and the bigger plunge-divers experienced the same force per neck area during a dive. Total force rises with neck size, but the stress on tissue stays the same. Both groups hit peak force nearly five milliseconds after impact.
Researchers Plan to Trace Force Down the Neck
The researchers say they want to examine in more detail how force travels down the neck. They also suggest the structure-function link could help paleontologists spot plunge-diving birds among fossils.
Co-authors include Adam P. Summers, Ed Habtour and John Michael Racy of UW, and Alissa Perez of the University of California, Riverside. Funders include the U.S. National Science Foundation and the Beatrice and Samuel A. Seaver Foundation, along with a Friday Harbor Laboratories Research Endowment Fellowship, a University of Washington Friday Harbor Laboratories Award, and Jim and Camille Uhlir. Vanderberg said the finding was something I didn’t previously think about and probably overlooked before
, and that she is curious to look more closely at vertebrae in general, not just in birds
.