Unfortunately, in most wildlife photography, if you've missed the eye, you've missed it all. That depends on its latitude. Because of that, both types forgive exposure errors. Your photo lab can pull a reasonable print out of either color negative film or black and white film, even if you erred by as much as two stops. Professional and serious amateur nature photographers shoot mostly color slide film, or chromes, because that's what editors require for publication.
Chromes have much less latitude.
In fact, slide film cannot properly record more than one stop off of a perfect exposure setting. Miss by more than that, and the colors are either all washed out or too dark to show detail. Since it s impossible to record the range of colors of the common loon on slide film, the answer is to set your exposure for the detail that s most important. With a common loon, that's the white. While this technique underexposes the black head of the loon and makes the water a bit darker than you might normally expose for, it keeps the white from blowing out and ruining your picture.