I think you are using the wrong lens.


Suppose Mr. Hummingbird there is about 2 inches from head to tail. @ 400mm, your 100-400/4.5-5.6L IS has a maximum magnification of 0.20x, which means that your subject will occupy about 10mm of a 24x36mm frame. That's not bad, but you could do better and sharper with a macro lens. Clearly, as close as you think you are presently, you are not close enough to MFD to render the subject sufficiently large. A macro lens is not just for bugs and flowers, and it doesn't have to be used at 1:1.


My suggestion? Bring the feeder to the camera. If you can, use the 180/3.5L macro, or 100/2.8 macro, and a wireless remote. Place the feeder right in front of the camera, and hummingbirds will ignore the camera as long as it's not moving and you're not standing close by. Then release the shutter from far away. You won't have to guess with MF if your subject is so close that it fills the frame and you are stopped down.


As for lighting, macro twin light flash, or off-camera strobe with softbox. Or just natural daylight with a white reflector on a stand.