Welcome once more to ornithology corner, that popular new part of the Gray Matter service. After my query some weeks ago concerning marauding seagulls around my house, which was so wittily answered in the letters column of The Oxford Times, I turn my attention today to sparrows, or rather to one sparrow in particular.

This little fellow - I have come to think of him as male, but could easily be wrong – has taken up near-permanent residence in a window box just beyond the French windows of a first-floor room at the back of the house.

He is utterly unfazed by my presence in the room, no matter how close to him I come to him on the other side of the glass.

On the contrary, he seems positively pleased to see me, tapping enthusiastically on the glass with his beak – rat-a-tat-tat – whenever I appear.

But his activities don’t stop there, for this endearing bird goes on to perform – once my attention has been gained – what I can only call an acrobatic display.

From his base amid the row of flowerpots in the window box, still containing living plants follow our fairly mild winter, he flutters upwards to rest on top of the metal balcony that extends halfway up the windows.

After this, with astonishing celerity, he executes a series of elliptical motions that take him to the upper reaches of the glass and back to his balcony perch. On each ascent he gives a tap on the glass with his beak.

Our first guess was that he was perhaps gathering material for nest building or eating small seeds caught in cobwebs. But his routine has gone on so long now that supplies must be exhausted.

Anybody any ideas?