Adjusted "shadows and highlights" a little.
Selected areas of each bird and adjusted brightness and "texture" settings using the NIK Viveza plug-in.
Brightened the eyes and increased the brightness and contrast of the "catch lights" at pixel level.
Slight noise reduction.
Selected the bird with the "quick selection" tool. Sharpened selected area using "smart sharpen" @0.3px, 150%.
Slight tweak to the tone curve to add some contrast without blowing the highlights.
Subtle, but maybe a little better?