From birds to trains - and back to birds

So what's this got to do with anything, I hear you say. Let me explain.

The thing is that my wife and I met a group of "twitchers" recently, and they were truly experts in their chosen field. Now, I may know a fair bit about birds but these chaps were Rembrandts to my pavement artist.

It was my wife who first noticed a possible link. After one member of the group began what can only be termed a St Vitus dance after spotting a nightjar, she gently inquired as to whether this gentleman had always been a man of ornithological leanings.

"Why yes," he said, " but before that, I was a trainspotter."

Quad erat demonstrandum.