In the case of binoculars, bigger is not always better! If you choose to use a higher magnification (i.e. 10 power) you may see the bird closer and larger, but the field of view will be smaller, and you must hold your hands very steady to keep it in focus. And a large lens size (42-50+ mm) offers a wide field of view, but the optics will be much heavier for it. Choose a pair that is most appropriate for your needs.
The number 7.7 degrees references the field of view, which in itself is not usually a decision-making factor for most birders. And speaking of numbers, Nikon also includes the 7-digit serial number of the individual equipment on their optics, which is useful if you need to reference them.
photo © adrian binns