The gannet’s dive

Gannets have evolved some very strange adaptations that make them some of the best divers in the natural world.

Northern gannet
Andreas Trepte, CC BY-SA 2.5, via Wikimedia Commons

Gannets live on little fish that swim near the ocean’s surface. They catch these fish by taking a perilous dive directly into the ocean at speeds up to a hundred kilometres an hour, and gannets have been observed plunging more than twenty-five metres under the surface. To make such a dive possible, these birds have a range of surprising adaptations that prevent them from a) drowning themselves, b) concussing themselves, and c) breaking their wings off with each dive.

First, when they go under, how do they prevent water shooting up their nostrils at the speed of a car on a motorway? The evolutionary solution delighted me: gannet nostrils are inside their bills. Closing their nostrils, therefore, is as easy as closing their mouths.

Second, when they hit the surface of the water, how do they handle the shock? Gannets have natural airbags. As they dive, they can push air out of their lungs and into air sacs in their face and chest. These inflatable pockets cushion their bones against the impact and ensure the bird’s survival.

Third, how do they stop the dive from shearing their limbs off their bodies? As they plummet, gannets fold their wings up against their bodies. This reduces their ballistic coefficient significantly. The diving gannet resembles nothing so much as a falling bullet:

Diving gannet
Mike Pennington, CC BY-SA 2.0, via Wikimedia Commons

All of this comes on top of the standard seabird adaptations (waterproof feather coating and eyeball membranes). The gannet’s dive is an impressive and refined hunting mechanism. To keep themselves aerodynamic (hydrodynamic?) the gannets even swallow their prey while they’re underwater.

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