Every year I know when the season is about to change without even glancing at my calendar. That's because, despite living 20 miles from the centre of London, I have a regular annual visitor who predicts it perfectly.
As winter draws in, the peach-brown feathers of waxwings appear in the rowan trees, attracted by the abundance of berries which, at this time of year, become scant in their native Scandinavia. Just weeks ago they were replaced by the blue and white house martins, newly arrived from northern Africa and tropical Asia to nest in the eaves of my house.