In general, to get a proper exposure, unless you are a very experienced photographer, the Exposure Compensation button is needed whenever the metered shot appeared incorrect. The rule is: To keep white white, over-expose; while to keep black black, under-expose. It applies to everything, even in portraits. This is because the camera meter everything at 18% grey tone.
From what I remembered reading from Arther Morris' book, one can spot metered on the white or black subject to obtain a reading. Then use the EC to ajust for the correct exposure. He illustrurated a complex chart, even based on the brand of film in those days, for the compensation factor for varying tonal color of the bird.
To obtain the correct tonal exposure is not the same issue as the correct White Balance. WB refers to the correct color temperature for the lighting in deg K. The scale is counter intuitive, such that the warmer color shows a lower color temp while a cooler color shows a higher color temp. To understand further as to when WB should be adjusted, please see:
http://www.kenrockwell.com/tech/whitebalance.htmFor an even more complex understanding of exposure latitude of digital photography, I found this article most illuminating based on Ansel Adams' (the greatest landscape photograher) work in tonal exposure:
http://www.outdoorphotographer.com/how- ... ystem.htmlHope this is helpful.
Good birding and photography.