A photo from my recent lunch hour sessions trying to photograph dipper on a stream near the office. I am always amazed how easy it is to walk past one depsite their incredibly bright white breast which is not good when you only have about 20 minutes camera time!
Taken with 1DmkIV with 1.4TC at ISO400 F7.1 at 1/640s -1EV.
Love the low angle, eye contact, and detail. With the Mark IV, you should be able to recover quite a bit of detail in the darks. For birds like this you might consider adding 1/3 to 2/3 of a stop of exposure; you'll get more detail in the blacks and can easily pull back the whites in post-processing.