It's all about wildlife photography...
Twiching is a British term used to mean “the pursuit of a previously-located rare bird.” In North America it is more often called “chasing”, though the British usage is starting to catch on there, especially among younger birders. The term twitcher, sometimes misapplied as a synonym for birder, is reserved for those who travel long distances to see a rare bird that would then be ticked, or checked off, on a list.
Birdwatching or birding is the observation of birds as a recreational activity. It can be done with the naked eye, through a visual enhancement device like binoculars and telescopes, or by listening for bird sounds. Birding often involves a significant auditory component, as many bird species are more readily detected and identified by ear than by eye. Most birdwatchers pursue this activity mainly for recreational or social reasons, unlike ornithologists, who engage in the study of birds using more formal scientific methods.
It is simply the photography of all types of wildlife (fish, birds, mammals) whatever takes your fancy. Some people include plants and wild landscapes (it is all nature). For most people this is a hobby and ties in with them also being interested in wildlife and walking and travelling. A few lucky people manage to make a career out of it but it is probably the hardest form of photography as animals are generally nervous and unpredictable, hard to find and remote.