h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Please check your definitions of 'twitcher' and 'birder'. A 'birder' or birdwatcher is someone who enjoys looking out for birds, perhaps in the garden, on holiday etc. A Twitcher is someone who keeps a 'list' of birds they have spotted, and will spend huge amounts of money getting to a remote location on the offchance that they may see a rare South African Lesser Spotted Spindly Killer Bird before it flies off.

Further clasification of the human sub-species is simply unnecessary.
There are many types of Tiger, for example, I would not like to meet any Tiger in a Pub, on a train or in a lift. The sub-species is immaterial.
I would apply the same logic to Birdwatchers.