Wildlife photographers generally have big lenses that cost lots of $$$ but more of an issue is the infinite patience required. Birds in particular are very difficult to shoot because they flit around at high speeds and rarely land for more than a few seconds. The background is very important as well (a good sharp photo of a bird with a distracting background makes for a bad picture).
What springs to mind is a talk given by a wannabe wildlife photographer at the Nanaimo Kayak club a few years back. He would go out for three months at a time – dropped off from a ferry near an island in the rain forest in an inadequate blow-up kayak that did not have enough room for the all the gear he should have had. Without enough food for the period, he typically lost 20-30 lbs over the course of the trip. He had to build a lean-to that was often inadequate for the rain in the “rain forest” so he was mostly wet all the time and occasionally got his camera gear wet as well.
Then there were the photos. He was trying to take pictures of grizzlies. Most of the photos were of grizzly paw marks. The only photos of grizzlies he did get were of their rear ends as they ran in the opposite direction. The one time he did get close enough with a grizzly coming towards him he didn’t get the shot because he was so scared, he grabbed his gear and left.
Having said that, I have taken a few trips to take photos of Grizzlies up to Glendale Cove via Telegraph Cove and probably will do it again. However, I will not pretend to ever be (or want to be) a wildlife photographer. It’s just too difficult.