And Fi­nally

Gan­nets leave fish with nowhere to hide

World of Knowledge (Australia) - - Contents -

This is the mo­ment Bri­tain’s largest seabird turns into a two-me­tre ar­row. The North­ern gan­net an­gles its wings just above the wa­ter to stream­line its body be­fore break­ing through the sur­face like a bul­let. Plum­met­ing from 30 me­tres up, the bird can dive to a max­i­mum depth of ten me­tres. Gan­nets hunt in a flock, so when they dive it’s like a ma­chine gun pep­per­ing the sur­face of the wa­ter.

Each bird ex­erts an enor­mous amount of en­ergy dur­ing a dive: tak­ing in seven sec­onds’ worth of air, Morus bas­sanus grabs a fish from the rapidly di­vid­ing shoal of her­ring, avoids col­lid­ing with other birds or dol­phins un­der the wa­ter and races back to the sur­face. The slight­est er­ror in cal­cu­lat­ing the en­try an­gle and the 100km/h hunter would be­come just a pile of feath­ers float­ing in the At­lantic.

The gan­net’s en­tire anatomy (in­clud­ing closeable nos­trils and a ster­num that acts as a shield to pro­tect its or­gans) is geared to­wards its kamikaze-style hunt­ing tech­nique. Closely re­lated to the booby, the birds share many of their hu­mor­ously monikered cousin’s idio­syn­cra­sies. Like them, gan­nets wad­dle a bit when walk­ing on land, but only be­cause their feet are lo­cated to­wards the back of their body. Their hunt­ing tech­nique is also al­most iden­ti­cal, and though their wing­span is larger at an im­pres­sive 180cm, they are sim­i­larly eco­nom­i­cal when it comes to their flight mus­cles. Both species use them only around 13% of the time. But does this in­hibit the per­for­mance of the largest bird in the North At­lantic? Not at all! In­deed, ev­ery year, 150,000 of them glide their way to Bass Rock in Scot­land’s Firth of Forth, mak­ing it home to the largest colony in the world.

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