The northern white-faced owl, found in the Sahara Desert of Africa, is a small, cute bird of about 22~24cm length. It is famous for a very unique defence mechanism. As shown in the photo, it normally has a round, puffy appearance, but when faced with a fearsome predator like a hawk, it undergoes a drastic transformation. The owl shrinks itself as much as possible to avoid the enemy’s attention, while looking like a sick bird that has lost a lot of weight. This appearance gives the predator the impression that the owl is not worth the effort of hunting and lowers the chance of it attacking. The ability to shrink to half its original width is achieved through elongating its body and pulling in its feathers as much as possible. Also, when assuming this shape, the owl always faces the predator and poses at an angle to minimise its exposure.
This transformation is only seen when the owl is placed in front of a large predator like a hawk or a much larger owl. When in front of a similarly-sized owl, it exhibits a different transformation where it flares up its wings to make itself look much larger, intimidating the opposition. But this behaviour is common in many other species of owls, whereas the shrinking performance is a rare behaviour only seen in the northern white-faced owl.
(Video showing transformation: http://www.youtube.com/watch?v=gFwgblszf6s)