Friday, 7 September 2012
Fit for purpose - puffin versus tern
With no visitor boats arriving I was in our visitor centre having a tidy up and looking at the touch table. It struck me about the huge contrasts between the wings on it. In particular I was looking at the difference between the puffin wing and the tern wing, you can see a picture of both above, the tern wing being the top wing. So here a few facts to show the differences:
Puffins wings are on average about 160mm in length. But their body weight is about 400g, quite heavy for such small wings. But actually puffins are not bad fliers, it is just the stopping and starting that they are not very good at and even then usually only when the wind is against them. These small wings have to beat very fast to keep a puffin in the air, about 3-400 beats per minute and once it gets going then it can go fast, very fast, some have been recorded to go at 94 km per hour. The small wings have another purpose, they are used half closed for swimming underwater after their food, fish. But though small, stiff wings perform better underwater it is thought that originally puffins evolved small wings so that they could fly fast and direct.
An average Arctic tern wing is 270mm long, as you can see much longer than a puffin. When you see terns fly past they look quite big birds but the actually only weight about 100g, a quarter of a puffins weight, about the weight of a blackbird. So why do they need such huge wings? Well arctic terns are long distance migrants, probably the longest of all birds. They fly huge distances, one individual was ringed on the Farne Isles in June and appeared in October of the same year in Melbourne, Australia, that about 22000 km in 4 months and so need to do this using the minimum of energy. And though they hunt fish like puffins, their big wings don't get in the way underwater as they are surface feeders and hover about the water to dive to catch fish that come up to the surface.