Steve2014 wrote:
I was about 50 feet from the birds and couldn't get any closer. Any movement on my part scared them away so I tried to hide just be ready when they landed. Not easy at 25 degrees. Light was a lightly overcast day about 2pm. Yes it was underexposed, I'm guessing -1 to -1.5 stops so I did try to bring it up with brightness and contrast in post.
All this is what every "birder" has to deal with all the time. Work on your stalking skills, set up a blind, use attractants to get the birds to come closer and to land in a more favorable location for a photograph... all these might help. This can take hours or even days or weeks working with the critters. PATIENCE will be your most valuable tool.
With wildlife, and particularly birds, I'll often take 50, 100, 200 or more shots to get one or two good ones.
That's a very difficult situation to focus, through branches like that. It also usually doesn't make for very good photos. Sometimes the best you can do is wait and watch, until there's a better opportunity.
Stopping the lens down a bit might have helped. You're settings are close to wide open. At 600mm that lens is f/6.3, if memory serves. EXIF says f/6.7, which is only 1/3 stop down from wide open. Most lenses are not at their best at their largest aperture.
If you'd stopped down more, you would have needed a higher ISO. People think they need to use the lowest ISO possible, but the truth is that doing so when it forces too large an aperture or too slow a shutter speed will ruin the image anyway. Underexposure was probably caused by relying upon auto exposure and the bright sky behind the birds fooling the camera into shooting too dark an image. But you are already using nearly a wide open aperture and relatively slow shutter speed. The lens might have stabilization, but that won't do anything to stop subject movement. 1/125 was really marginal. You used ISO 200... might have been better off at ISO 1600! (I don't know your camera or it's high ISO performance... these are things you need to test yourself.)
Any time you have to brighten an image in post-processing, that will greatly increase the appearance of noise in the image.
A lot of the time flash is needed, especially in backlit situations like this (however, it wouldn't have worked in this case because of the branches between you and the birds). To use flash with powerful telephotos means using a rather powerful flash, putting it on a bracket of some sort to raise it off the camera further and attaching it with an off-camera shoe cord and using a "flash extender" with focal lengths longer than 300mm.
Welcome to the world of long lens shooting and birding!