Being transparent

[Tom Barry]

A young black-chinned hummer. These wiggle their tails while hovering, as can be seen by the ghosting, whereas the similar ruby-throated hummers do not. Two remote flashes. The background was not lit by flash, so as to show ghosting.
Black-chinned hummingbird by tombarry975, on Flickr

[Wavelength]

Masterly!!! Fantastic!!!...shutter speed?

[Tom Barry]

Shutter speed was 1/250th sec. The two remote flashes were set to 1/32, which means they flashed for about 1/9000th sec. They were about 2.5 feet from the hovering bird, one to the left front and one to the right front and the brief burst dominated. Because there was some ambient light and the background was not flash-lit, the bird’s rapid wing and tail movement during the 1/250th sec. the shutter was open were not entirely frozen. Also, the wings were hit by flash from both sides and, being quite thin, exhibit transparency.

[Wavelength]

But how you could set up remote flashes, since this might be a sudden incidence

[Tom Barry]

I have two feeders under the eaves of the house on the back deck of our house. When I want to shoot hummers I move one of them to a stand on the deck and place the flashes on stands. If I want to freeze the wings, I place a painted background behind the feeder and place a third flash to light it. Even when flowers are blooming, hummers will come to the feeder every 20 minutes or so. When a bird comes to the feeder, it will almost always hover for a moment before moving in to take a few sips of nectar. Then it will back away and hover a moment while looking around. As I dislike having the feeder in the shot, I wait for the hovering moment before pressing the shutter. I either hand-hold the camera or have it on a tripod, and almost always use manual focus, pre-focusing on the hovering point. Stopping well down gives sufficient depth of focus.

[Wavelength]

Ok, thank you for the explanation