Fat, young shearwaters are known as mutton birds on Australian Islands.

The mutton bird is another name for a kind of seabird known as the shearwater.  Shearwaters are very fat when young and are considered good to eat, especially on Australian islands where they are known as mutton birds.

Mutton Bird

The shearwater’s real name comes from its habit of shearing or skimming close to the water as it soars just above the waves on its long, slender wings.

The shearwater can glide for many hours, riding the air currents with barely a wing beat.

The shearwater comes ashore only  to nest, usually on an island where it can be safe.  Here it lays one large while egg in a hole dug in the ground.

The young chick grows up slowly and becomes extremely fat, and weighs more that its parents.  At this point, the parent shearwaters simply fly off, leaving the fat chick entirely alone, to live only on the fat in its body.

In about a week, the young shearwater has slimmed down and comes out of its underground nest to exercise its new wings, then flies off. It may be three to four years before it returns to land again.  – Dick Rogers