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

Sharon Sneddon answered on 21 Jun 2010:

Hi Oulay, was great to chat to you earlier!

I’ve found an answer to your question from a book called “how birds work” so if you are interested in finding out more, then maybe your library will have it!

Humming bird’s wingshave elongated hand bones to which the flight feathers are attached, and the whole wing can rotate like our wrists.

The short arm bones not only allow movement in all directions but also lets the wing rotate through 180 degrees. The tips of the wings can achieve a lots 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 lift and forward motion.
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 really good at this, but it does not constitute true hovering. Humming birds are able to maintain their hovering in perfectly still air and hey are the only birds which can fly forwards, backwards, up, down, sideways or move instantaneously in any direction.

Hope this makes sense!