"What's that incessant tap-tap-tapping at the lounge window?" I thought to myself.

I peered around the curtain, and came face to face with this:

Yes, it's Mr House Sparrow.

He doesn't want to come in. Instead, he's there in active combat, fighting a particularly dogged rival. The window forms part of his territory, and yet to his irritation a stubborn if silent male sparrow seems to have taken up residency just inside the window.

Each time Mr Sparrow jabs at the intruder, the intruder jabs back.

I watched as he then moved along the window sill and, you know what? The rival moved along, too!

It is likely that these little episodes in which male birds meet their mirrored match are breaking out all over the country right now. The hormones are rising as the days get longer, and that brings out all their territorial instincts.

A couple of years ago for me, it was a Long-tailed Tit at my study window who made repeated visits to fend off his nemesis:

Robins are especially agressive, so they are especially prone to attacking darkened windows and especially car wing mirrors, as are Blue and Great Tits. Pied Wagtails, too, can be caught up in the never-ending sparring sessions. Have you had other species caught up in these battles?

The simple solution is to just remove or reduce the mirror effect - put something light coloured in the spot where the bird taps, or put a cloth or bag over the wing mirror while the car is parked up. Then the males can save their energy for real rivals, and for all the stresses and strains of the breeding season to come!

And you get spared the headache of the tap-tap, tap-tap, tap-tap...