While I have had occasion to use a wide angle in up close and personal situations with wildlife, the more frequent reason for attaching this lens is to show the animal in its environment. If the scene holds as much significance as the animal, include it. This being the case, to incorporate the background in the composition, use a wide-angle lens. The exact focal length is determined by how much scenery should be included, in addition to how close the photographer is to the scenery and animal. The closer in, the wider the lens.
Benefits: When you shoot with a wide-angle lens, a lighter tripod can be used than if you photograph with a super telephoto. Since the animal is farther away, a slower shutter speed can be used to stop the subject’s movement, as its proximity doesn’t reveal as much motion as when the animal is close. This means lower ISOs with less noise. Depth of field is greatly increased due to the wide focal length, which allows the photographer to use a wider range of shutter speeds. Shorter lenses are much less expensive than long telephotos. Finally, it’s easier to create a composition more quickly, as you don’t need to “find the subject” in the narrow angle of view of the telephoto.
Some subjects are very tolerant of humans, and in some locations throughout the U.S., a subject that may take flight will let you approach very closely since it’s acclimated to human presence. Take for instance the birds in many Florida locations. If I try to approach a great blue heron in Colorado, it flies long before it’s in telephoto range. The same species in the Everglades lets me get frame-filling shots with a wide. Will I ever abandon my telephoto? Of course not. But I will always be found with a wide angle next to me while I use it!