The effects of a telephoto increase with focal length. On a crop-sensor DSLR, a 50-200mm, 50-250mm, 70-300mm or similar will be more than powerful enough while on a full-frame DSLR a 70-200mm, 70-300mm or 100-400mm will serve you well. You can also crop full-frame images during postprocessing to emphasise the telephoto effect – since you’re starting with a bigger image file, it doesn’t matter if you crop some of it out.