Friday mystery object #129 answer

On Friday I gave you this object to identify:

This type of bone can prove tricky to identify, and we often have queries about them on Ask A Biologist. With a large example like this one there will often be a suspicion that it comes from a human

However, this is in fact the humerus of a bird – the large flange at the proximal end (the bit nearest the body) makes it hard to spot the rounded point where it articulates with the scapula, coracoid and furcula bones that make up the shoulder joint. The flange itself provides a large attachment area for the tendons and muscle needed to power and control flight.

Here are some images of a (much smaller) goose humerus that show the general structure of the bone more clearly:

Once you’ve recognised the mystery object as the humerus of a bird, the length of about 45cm (17.7 inches) immediately narrows down the species it could come from.

Jack Ashby was the first to recognise what this humerus belonged to and he found support from Rachel, Carlos, Julie Doyle and initially Barbara Powell (although she later opted for another possibility). It’s the humerus of an  Albatross, most likely the Wandering Albatross, Diomedea exulans Linnaeus, 1758.

The Wandering Albatross has the largest wingspan of any living bird, up to 3.5m (that’s about 11 feet 7 inches) and they use those long, thin wings to generate lift from the tiniest breezes. In fact, they can fly thousands of miles with barely a flap of their wings by using a fascinating flight strategy known as dynamic soaring.

Dynamic soaring uses the difference in airspeed between the slow air in the troughs of waves near the ocean’s surface (it’s slower because of the friction between the air and the water) and the faster moving air above (where there is less friction). When the bird is higher up it has a store of potential energy from gravity, which is converted to kinetic energy as it drops closer to the water, increasing the speed of the bird as the speed of the wind decreases.

This is important, because the lift needed to keep the bird aloft is dependent on the speed at which air moves over the wings.

As the bird reaches the slowest moving air near the water it uses its residual speed to turn up and face into the wind, which generates enough lift across the wings to bring the bird back up into the faster wind above. This generates much greater air speed and therefore lift, giving the bird greater height and more potential energy to repeat the cycle.

The actual process is more complex than this, as the bird can use the interplay between the wind, the wave troughs and its wings to tack into the wind, to move along a wave or to follow the wind direction.

The beauty of this strategy is that it uses very little metabolic energy, so the birds can cover huge distances in search of food floating on the surface of the vast oceans. Albatrosses truly are the masters of the sea air.

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