Gannets are supremely adapted for plunge-diving. They lack external nostrils and have air sacs under their skin to cushion the impact of striking the water. The full force of the strike is further minimised by their streamlined body form, and miniature accelerometers attached to gannets reveal that there is little effect on the birds as they hit the water, allowing them to maintain their momentum beneath its surface. Indeed, gannets typically slow their descent when they reach their prey by flaring their wings and feet.
The depth to which gannets plunge depends on the speed at which they enter the water and this is related to the height from which they dive. When feeding on prey that is well below the sea surface, gannets climb to some 40 metres above the water and then rely on gravity to accelerate up to 90 kilometres an hour and penetrate the water almost vertically. However, they can also dive at shallow angles, speeding up by flapping until just before they enter the water, when they extend their necks and stretch their wings back to smoothly break the surface.
この記事は African Birdlife の March/April 2022 版に掲載されています。
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この記事は African Birdlife の March/April 2022 版に掲載されています。
7 日間の Magzter GOLD 無料トライアルを開始して、何千もの厳選されたプレミアム ストーリー、9,000 以上の雑誌や新聞にアクセスしてください。
すでに購読者です? サインイン
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