Gannets are not only the largest, but also one of the most impressive looking of Britain’s seabirds with a 2m wingspan, long neck and pointed beak and tail. They are perhaps best known for their highly specialised hunting technique, which has led them to develop a number of remarkable adaptations. Gannets are plunge divers; their shape is remarkably streamlined to enable penetration of both air and water and they have binocular vision, which enables them to spot their prey from heights of up to 30m. They will initiate their dive, dropping from the sky and hitting the water at an astonishing speed of up to 60mph; the deepest dive recorded from a Grassholm gannet was 22.2m.
The impact associated with hitting the water at that speed is immense and to minimise this, a split second before they enter the water, gannets fold their wings back against their bodies to increase their streamlining, their pointed bills breaking the surface tension as they pierce the water like a feathered dart. They rely largely on their momentum to carry them through the water, but can also use their feet and wings to propel themselves deeper to reach their prey. Further adaptations include internal nostrils that can be closed when in the water to stop water ingress, reinforced skulls, air sacs in their body which inflate to cushion the impact with the water, and a secondary eyelid which comes across to protect their eyes. All in all they are a highly adapted hunter. Gannets may come back to Grassholm as early as February and will lay their eggs in mid April, incubating them for 43 days. It takes an incredible further 90 days before the chick is fully-fledged and ready to leave the nest; they will finally start leaving the island in early September. When they first hatch, gannet chicks are black, leathery and slightly prehistoric looking, until they turn into white powder puff balls, with their juvenile plumage eventually turning dark brown. This latter colour has the disadvantage of not being camouflaged for hunting, but it is thought to protect them from the unwanted attentions of naturally aggressive adults, as it marks them out as youngsters.
Despite being doting parents, gannets are hostile neighbours and life in the colony often involves a lot of squabbling, particularly during take off and landing which, despite their aerial prowess, is a pretty clumsy affair with a distinct lack of spatial awareness. Fledgling gannets weigh about 4kg and are too fat to fly when they first leave their native colony. An ungainly scramble and tumble, often causing chaos with the neighbours on the way, will take them to the water’s edge where they will take the plunge and bob about, looking slightly bemused in their new environment. Once on the water, and initially paddling, they will start their migration to the coast of western Africa where they are likely to spend their first couple of years before returning to their native colony.
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