Joe, to be honest, there's a lot working against you in the photo. You've shot almost directly into the sun with the eagle silhouetted against the mid-toned sky. By upping the exposure on the entire image, you're probably going to blow out the sky. You are probably not going to recover a heck of a lot of detail in the eagle since it is so under-exposed. You could attempt to use an adjustment curve in PS, but they're pretty finicky, especially when dealing with 8-bit JPG images. If you've shot this in RAW, there's hope in using Canon Digital Photo Pro and upping the Shadow slider, which could recover a bit of eagle detail without blowing out the sky, but again this is of limited utility.
My best advice is going to sound trite and snarky, but in all honesty, I would record this as a learning experience and make an effort to shoot test shots while in the field to judge exposure. I would typically meter on a mid-toned object in the same generally vicinity to find out the correct exposure for a backlit subject and then manually expose or use Exposure Compensation to "overexpose" the background or at least to avoid it fooling the meter like in your shot here.
If this sounds a bit complication, I would highly recommend Brian Peterson's Understanding Exposure
. To get a handle on tricky lighting down the road. It helped me immensely when I was starting out with wildlife photography.
Backlighting is one of the most challenging conditions and you have to figure out what you're willing to lose: either let the sky blow out by using +1 or even +2 EV, or lose the details in the subject and allow it to fall into shadow or even a silhouette. Either of these choices can work for the final product, but it's an either or unless you're shooting RAW (and even then might not be completely possible to recover both).
I hope this helps.
