A bit of an animal

Sarah Harrison, one of our long term volunteers writes:

One of the things I have been doing recently is writing new information labels for the touch table objects. This means I’ve been looking closely at seabirds’ beaks, wings and feet and doing a bit of research, learning why the seabirds which breed on one small island have such a wide variety of body shapes.

For starters, there are huge differences in wing shapes, for example between arctic tern and razorbill wings. If you compare them you can see that the terns have much larger and longer wings, especially if you consider that the razorbill is a much heavier bird (a tern weighs about 100g and a razorbill about 700g).

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In this case, the cause of this difference lies in how the birds use their wings, because wings aren’t just for flying!

The terns are flying specialists and their wing shape makes them energy efficient and manoeuvrable fliers. They need the energy efficiency so they can fly for long periods without resting during their long migration to Antarctica, and the manoeuvrability so they can chase fish from the air. It is interesting that terns are compared to swallows, often being called the ‘swallows of the sea’. Terns and swallows are not closely related, but because they both migrate long distances and feed in a similar way (swallows catch insects on the wing) they have evolved similar body shapes.

Razorbills also eat fish, but unlike terns they catch them by diving underwater propelled by their wings. Small, short wings are the most energy efficient shape for wing-propelled swimming, but the smaller wings get the more difficult it is to fly. The razorbill wing shape is a compromise – small enough for swimming, but large enough to keep the ability to fly.

Razorbills, puffins and guillemots all belong to the same family of seabirds (the auks) and have all evolved similar flying/swimming wings. Guillemots have the smallest wings compared to their body size, making them the the poorest fliers but best swimmers of the three auk species on the May. Research carried out on the island has shown that during fishing trips guillemots spend less time flying than Razorbills or Puffins but make longer, deeper dives.

The ability to make long, deep dives allows guillemots to specialise in catching single, large fish for their chicks whereas puffins and razorbills catch several small ones. You can see these differences reflected in beak shapes – guillemots have a long, pointed beak in which they hold one fish lengthways, whereas razorbills and puffins can hold several fish crosswise in their broader, flattened beaks. Puffin beaks even have a special hinge which allows them to keep tight hold of fish at the back of their beak whilst opening it to catch more at the front – perfect for bringing home a huge beakful of fish to feed a hungry puffling!

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Puffins aren’t just good at fishing, they are also expert diggers. They dig their burrows using their feet, and have a special claw that helps speed up the process. The third claw on their foot grows sideways, so it isn’t worn down when the puffin walks around, keeping it curved and sharp. The sharp claw is also useful for another important puffin behaviour – fighting with other puffins! They may look cute, but puffins will fight viciously to defend their burrow from an intruder, probably because it takes a pair a whole breeding season to dig a new one.

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So next time you’re admiring the birds on the May it’s worth taking a moment to wonder about how they have become the way they look today. So many things could potentially have affected the way a seabird’s body shape has evolved – including how it builds its nest, how it catches its prey and how far it has to travel. The birds all look so different because they have all found different ways of surviving to breed on the May.

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