Sandy, the moment I saw this image I thought it was stunning!
As for the lighting, my guess is that it was taken in the evening or perhaps early morning – hence what appears to be the somewhat golden colour hitting the robin's breast almost horizontally. If that's the case, I'd be tempted to leave it as it is although a very slight lightening of the right side of the birds head might be helpful.
I'm curious how you got this photo. You don't say what was the focal length of the lens but, whatever it was, the image gives the sense that you were lying in the grass somehow invisible to the robin. That's one of the reasons that the image turned out so well. Perhaps you had the camera sitting on something at ground level and a long cable release?