See the mosquito on this black bear cub's ear? The black bear is at the top of the food chain in Pennsylvania, but that does not mean they don't get bit. Getting bit is certainly going to be on the back of everyone's mind when photographing a bear cub this small as the highly protective mother is guaranteed to be nearby.
A mother bear nearby makes the zoom capabilities of the Canon EF 200-400 f/5.6 L IS Lens highly desirable. To capture this picture of a tiny cub required use of the built-in extender for 560mm of focal length (plus a small amount of cropping). To capture a full body portrait of the much larger mother (with or without cubs in the frame) required a wider focal length. Bears are very unpredictable and may not have tolerated (or stayed long enough for) a lens change. The 200-400 L lets me work fast, capturing the ideal framing potential from the situation.