At over 100 km/h, the northern gannet hits the sea headfirst without breaking its neck.
From the air, this seabird spots a school of fish, folds its wings and dives like an arrow. It can enter the water at around 113 km/h. At that speed, a human would risk serious injuries. So how does a bird with such a long neck withstand the impact?
Northern gannets
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Researchers from the University of Washington wanted to understand what happens in its skeleton. They examined the vertebrae of several birds preserved in a museum, then compared them with those of species that do not dive in this way. Scans allowed them to observe the bones in three dimensions.
The first difference is immediately obvious: in northern gannets and their close relatives, the neck vertebrae are shorter, wider and thicker. They look more like small solid blocks than the elongated vertebrae of many other birds. Their shape could distribute the forces experienced on contact with the water more effectively.
But the researchers also spotted a less visible detail. Between several vertebrae, there are additional contact surfaces that act as small supports. They are found in particular between the second and sixth cervical vertebrae. These supports could prevent the neck from suddenly bending backward during a slightly misaligned dive.
The bird does not rely on its bones alone. Before touching the water, it stretches its neck and contracts its muscles to keep its head aligned with its body. Its pointed beak and highly streamlined position also help reduce the force of entering the water.
The researchers found fairly robust vertebrae in other diving birds, such as kingfishers. However, they did not observe the same additional supports in them. Very different species therefore appear to have developed several solutions for performing a similar movement.
This study mainly shows that the shape of the vertebrae is closely related to the way these birds hunt. The researchers now want to study more precisely how forces travel through the neck at the moment of impact.
These features could even help identify the lifestyle of extinct birds. A fossil containing a few well-preserved vertebrae could reveal that an ancient bird also dived at high speed to catch its fish.