When purchasing a tripod for wildlife or action photography, a ball head is a must. A pan head does not move fluidly and can limit your response time to say a bird taking off and flying.
Weight is key. Most camera bodies weigh one to two pounds and take on a telephoto lens at another two-plus pounds depending on the size. If you are shooting subjects that more often require the tripod to be at a 30-70 percent angle, you will need to have a tripod that can support at least double your equipment's weight or the camera will sag and you will have to adjust accordingly.