Hummingbirds exhibit the amazing ability to
hover when sipping nectar from flowers and back-yard bird
feeders. Notice that this bird's wings appear to be
backwards! The leading edge of its wings - the roots
of the feathers - is behind the feathers. This is
because the wing during hovering moves horizontally
back and forth, not up and down as in forward
flight. The hummingbird in the photo is executing
the wing's return stroke; the bird has rotates its wing
bone (humerus) in its shoulder socket so that the leading
edge of the wing alternately faces the rear and front
during the complete wing stroke.
In the animated sequence at right one can see
that the wings are rotated alternately forward and back
for the forward and backward strokes respectively.
In both halves of the wingstroke, the feathers point
downward at an angle to give lift. In the final few
frames of the high-speed video clip the hummingbird
changes the pitch of its left wing in order that the left
wing gives some forward thrust and the bird begins to fly
off to the right.
Compare the hummingbird flight with that of the
Photo of the Week for April 8, 2011). The
technique of rotating the wings with the return strokes is
the same for both animals.
Hovering is very "expensive" for flying animals -
mainly because all the lift must be produced by the wing
motions. Birds ordinarily obtain a significant lift
merely from their forward motion through the air.
Only the smallest flying animals can hover for any
appreciable length of time.
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to firstname.lastname@example.org.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.