Migrant Bird

The migrant bird resembles 'Always-up'. It swings from side to side. When it leans out of the perpendicular 'Always-up'' has its centre of gravity higher compared to when it is vertical. In the case of the bird both rising and lowering its wings (and rising its trunk) rise the centre of gravity.

The difficulty of the bird construction lies in finding proper proportion between the weight of the wings (which are heavier than the trunk) and finding proper suspension point. As it can be seen in the sketchy pictures, the angle at which the wings rise and the location of the suspension point bring about the rise of the centre of gravity; once the trunk lowers - the wings rise above it. And vice versa: once the trunk rises the wings are in almost horizontal position, the suspension point is closer to the centre of gravity of the wings then to the central point of the bird, the centre of gravity of the trunk rises above the now lowered centre of gravity of the wings.

PSlow swinging motion of the bird is explained by the same rule which explains the swinging head of the dancing dog; long wings have considerable moment of inertia.