When photographing anything that has eyes - from people to birds to camels - the best connection with the subject will be if the viewer can make eye contact. That is usually best represented at eye level.
For wildlife, I do my best to move around to get to eye level. For ducks swimming on a pond, that usually means sitting down low on the bank or even laying down on the ground. For something taller, like a moose, I sometimes will stand on a small box. For taller animals, standing further away will also help you get to eye level or standing on a nearby mound, hill or ridge.
The reason for this is perception. Our minds perceive something that we look down on as insignificant (think of a boss standing over his desk yelling at an employee sitting in a chair). If we look up at something, our minds perceive that subject as superior to us (think of a child looking up at a parent). Shooting at eye level gives us equal significance.