Spectacular (and elusive) sightt of a gannet diving
Published 14/07/2015 | 00:00
I received a 'phone call from a photographer asking if I could suggest where he might go to get shots of Northern Gannets plunge-diving. It was a difficult question to answer as it was like asking where to go to get a good shot of a rainbow.
With a wing span of about two metres, Northern Gannets are the biggest seabirds that we have in Ireland. They feed on surface-shoaling fish and range far and wide searching for prey. When they find prey they plunge-dive and to see a number of birds fishing is indeed a spectacular sight.
However, like seeing a lovely rainbow, happening upon an impressive display of plunge-diving is a matter of chance and even then it is a fleeting experience soon over and maybe never repeated in the same spot.
A lot of birds have their eyes where we have our ears. That arrangement gives them better all-round vision but it is no good for hunting by sight. Birds like owls that hunt by sight have eyes that are positioned side by side and face forward.
Northern Gannets have the same arrangement of forward pointing eyes and binocular vision. Birds fly aloft with their necks bent and their eyes pointing down as they scan the sea surface for fish.
When a shoal is spotted near the surface the bird goes into a head-first power dive often from a height of 30 to 40m. The long, dagger-like bill points down, the long neck stretches straight, the wings fold back and lock in an arrow shape and the long, spiky tail feathers fan out as the now perfectly streamlined bird hurtles towards the water.
The results of experiments suggest that gannets hit the water at a speed of about 100km/h. Many must have broken their necks along the evolutionary journey before natural selection perfected the many adaptations that modern birds possess.
Adaptations include an extra thick, reinforced, crash-helmet-like skull, air sacs in the face, chest and shoulders, throat pouches that inflate like air bags to absorb the shock of impact and nostrils that are located inside on the roof of the mouth.
The impact may stun unsuspecting fish and carry the bird down 10m where it 'flies' underwater snatching prey.
The sight of Northern Gannets plummeting into the sea is indeed a spectacular one and is something to watch out for on a visit to the seaside. However, like the rainbow, it's a chance occurrence.