Hovering Hummingbirds

QUESTION: How do certain species of birds such as hummingbirds, terns, gulls and kestrels remain in the air without a forward motion?

Abhayakumar Shah, Adoni, A. P.

ANSWER 1: The humming bird's wings consist mainly of elongated hand bones to which the flight feathers are attached, and the whole wing can rotate as does the wrist.

The short arm bones not only allow movement in all directions but can also accommodate axial rotation through 180 degrees. The tips of the wings are capable of achieving a great deal of controlled movements. Birds have two sets of muscles operating the wings.

One powers the down-strokes and the other provides the upstroke or lifts the wings. A humming bird has more number of muscles to lift it upwards.

The angles through which the wings can be twisted and rotated by means of the big muscles that give the upstroke, can convert even the upstroke into a power movement providing both lift and propulsion.

Thus the bird is able to hover in perfectly still air, its quivering wings moving rapidly backwards and forwards rather than up and down, the tips of the primary feathers tracing a figure of eight.

Every time the beat is reversed, the wings are pivoted through 180 degrees, this ensuring that the front edge always leads, and on the back stroke, it is always the underside of the flight feathers which are on the top.

This means that although forward and backstrokes both produce lift the two actually cancel each other out and leave the bird still on station with no movement.

The kestrel and kingfisher are adept at this, but it does not constitute true hovering. Humming birds are able to maintain their hovering in perfectly still air, a feat totally beyond the kestrel which, true to its vernacular name of wind hover, cannot function unless a breeze is flowing, even though this can be so slight that at ground it may not be noticeable to a human observer. Reference: How Birds work. A guide to bird biology.

P. T. Sreelekha, Thrissur, Kerala

ANSWER 2: Wings of hummingbirds are adapted to a helicopter-like flight. They can move their wings from shoulder and can beat them up to 70 beats per second. They have two sets of flight muscles.

They are the pectoralis majors (one left and one right), which are attached to the sternum and keel, the upper wing bones (humerus), and the clavicles (which are fused at the tip to form the furcula, or wishbone). The pectoral muscles pull the wings down, which causes forward motion of the bird.

The wings are raised by the supracoracoideus muscles (right and left), which in hummingbirds are particularly large — about half the size of the pectorals.

Hummingbirds can rotate their wings backward, which creates downward 'lift' and backward `thrust'. By alternating their wings forward and backward, the up and down forces and forward and back forces cancel each other out, enabling the bird to hover in one place.

They are the only birds which can fly forwards, backwards, up, down, sideways or move instantaneously in any direction.— The Hindu S & T Desk