Virginia Tech's Sunny Jung spilled the beans on how he and his colleagues studied the physics of gannets diving into the sea to capture prey. Some may recognize Jung's name from prior work his lab has done on the physics of how dogs and cats drink water. A diving bird, from a physics standpoint, is essentially an elastic body impacting the water's surface, but the two mediums -- water and air -- are vastly different mediums in terms of density.
And that means the birds must be able to tolerate very strong forces upon impact. There's a huge stress on the animal body," says Jung. This is especially true for gannets, who hit the water moving as fast as 55 MPH in search of underwater prey, often up to 60 times.
They're like "torpedoes hitting the water," Jung said. Check it out:. Professional divers who participate in the Red Bull high dive competition typically make dives from heights of around 50 meters, and Jung estimates the impact force of such dives at around Newtons. It's quite dangerous; even a professional diver can fracture a leg or a couple of thoracic vertebrae if they don't hit the water in perfect position.
So how do the gannets manage to make high-speed dive after dive after dive without injury? Jung and his students collaborated with researchers from the Smithsonian's Natural History Museum to find out.
Jung et al. It is an ex-gannet! So they carefully arranged the gannet corpse in peak diving position and froze it -- manmade rigor mortis -- then dropped the frozen bird repeatedly into the tanks. Cameras captured the impact and mechanics of the bird's movement through the water.
This revealed three distinct phases of the dive. Phase 1 is the initial impact force on the head as the bird first hits the water's surface; this produces a slight compressive force on the animal's long neck as downward gravity pushes against the neck in one direction, and the upward impact force pushes in the other direction.
Phase 2 is when the head is fully immersed in the water but the body is still in air. At this point, the downward gravity pull becomes a drag force caused by the water, thereby producing a very strong compressive force on the neck. An air cavity also forms around the bird's neck. Phase 3 is when the animal's entire body is underwater with steady drag on both the head and body, so once again there is very little compressive force.
The danger zone from a diving standpoint is Phase 2. Jung's team then made 3D printed models of gannets based on CT scans of the dead bird courtesy of a local veterinary hospital and repeated the experiment.
They also made 3D printed models of what can only be described as "spherical gannets": reducing the biological reality to an elastic beam neck with a cone head and beak on the front end and a sphere body on the back end, and tried the experiment again, varying the length of the elastic beam, as well as impact speed, and the angle of impact with the water.
Physicists are nothing if not thorough. They then modelled how frequently the gannets travelled in flocks, the sizes of those flocks and the positions of young and adult birds. Birds travel in flocks for a number of reasons, including to reduce aerodynamic drag and therefore save energy. In addition, travelling in a group can improve hunting efficiency, navigational accuracy and predator avoidance.
The research also demonstrated that travelling in flocks may also facilitate social learning too. Habitats Coastal. Did you know? Bass Rock in Scotland is a famous nesting colony where masses of birds can be seen and, very definitely, heard!
How you can help As a charity we rely on memberships. Species Sandwich tern Found around our coasts during the breeding season, the large sandwich tern can be spotted diving into the sea for fish such as sandeels….
Gannets Over half the world's northern gannets nest on UK shores, with our coastal cliffs being home to some of the most important seabird…. Identify gulls Gulls are among our most difficult birds to identify. Birds are lured to the bait and get caught on the hook. Other fishing techniques can also form a threat to gannets.
Gannets are also susceptible to marine litter. A fishing crate containing three gannets washed ashore on Terschelling in August Because the birds need space to spread their wings in order to catch the wind and take flight, they were unable to get out of the crate. In November of that year, a gannet entangled in kite-surfing equipment washed ashore on Texel. Gannets like to follow fishing vessels, just like gulls. They go after the fish refuse and bycatch thrown overboard.
Luckily, when gannets have chicks to feed, they go after this healthier and natural source, even though it means diving more than twice as often than eating junk food. Sometimes you can see hundreds of gannets migrate along the North Sea coast from the beach on Texel.
If you notice that they are diving a lot, then there is lots of fish to catch. With a bit of luck, you may even spot a group of porpoises in the water! There is a permanent population of gannets at Ecomare. These birds were once brought there because they were unable to fly and therefore could not be returned to the wild.
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