Not quieter. Stops. You can stand with one foot each side of it in May at five in the morning and hear a dawn chorus in one ear and nothing in the other.
I am not a scientist. I record birdsong as a hobby, badly, with equipment that cost more than it should have, and I have done it since I retired.
The wood is about ninety hectares of mixed broadleaf on a slope, privately owned, and I have permission from the family who own it, which I have had for nineteen years and which I would like to keep, so I am not going to say where.
The line runs roughly north to south for about three hundred metres, and then it stops, and I have never been able to find where it turns or whether it turns at all.
I found it in the ordinary way. I was walking with the recorder running, which is how you find anything, and when I listened back that evening there was a place where the level fell off a cliff and came back thirty seconds later.
I assumed I had knocked the gain. Everybody assumes that.
So I went back with two recorders and put one either side of where I thought it was, forty metres apart, running at the same time from the same clock.
North one: a May dawn chorus. Blackbird, robin, wren, chiffchaff, a woodpecker somewhere.
South one: wind in leaves, my own footsteps arriving, and nothing else.
I have measured it properly since, as properly as an amateur can.
I use a sound level meter, a decent one, calibrated with a calibrator, because a recorder tells you about the recording and a meter tells you about the air.
At dawn in May, twenty metres north of the line: between fifty-eight and sixty-four decibels A-weighted, which is a normal loud dawn chorus.
Twenty metres south: forty-one, which is what a wood sounds like with the wind in it and no birds.
The transition is under two metres wide. I have walked it with the meter in front of me at arm's length, one slow step at a time, watching the number, and it goes from the fifties to the low forties across about the length of my stride.
Things it is not.
It is not a species boundary. The habitat is the same. Same trees, same age, same ground flora, same aspect. I have had a woman from the county wildlife trust walk it with me, without telling her why, and she said it was a nice consistent bit of wood.
It is not the wind. It holds on still mornings.
It is not a road, a pylon, a mast, a pipeline or a boundary of any kind. I have checked the deeds, the OS, the historic OS back to 1888, the tithe map, the LiDAR data that is free to download now, and the local historic environment record. There is nothing there. No bank, no ditch, no earthwork, no building, no track.
It is not my hearing, because it is on the meter and on two recorders and my wife has stood on it and gone quiet.
The birds go up to it.
That is the detail that took me longest to accept, because I kept expecting to find that they simply were not there, that the south side was empty of birds and that would be that, a food thing, a soil thing, something with a name.
There are birds on the south side. I can see them. I have watched a blackbird feeding twelve metres south of the line for four minutes with binoculars.
It did not sing. It did all the other things a blackbird does. It turned leaves over and it hopped and it flew off north, and when it was north of the line it landed and sang.
I have watched that happen, or something like it, forty or fifty times over six years.
The one exception, and it is the reason I am writing this down.
Twice a year, in the last week of October and the first week of March, the line is not there.
The meter reads the same both sides. The recorders agree. There is song right across it, and if you did not know where to stand you would never find it.
Those two windows are about eight days each and they are not the equinoxes, which I checked first. They are about five weeks after the equinoxes, both of them, and I have no idea what that means and I have stopped trying to make it mean something.
What I do now, in those weeks, is walk south.
I had never been more than about two hundred metres south of the line. Not out of fear. It is dense in there, and the going is bad, and there was nothing to record.
In the October before last I went in during the quiet week, with the meter and a recorder and a compass, because I wanted to know how far the silent area extends.
It is not an area.
Four hundred metres south of the line the wood is normal. Full of song, in October, at the level you would expect for the month. And it stays normal for as far as I went, which was to the far boundary.
So it is not a patch of silent wood. It is a band. About four hundred metres wide, three hundred long as far as I can trace it, in the middle of a wood that is otherwise ordinary on both sides of it.
A strip, roughly north to south, with birds all round it and none in it, for fifty weeks a year.
I measured the strip out with a tape in the March window, when I could walk it without it feeling like anything.
Three hundred and ninety metres by three hundred and ten.
I have not been able to leave that alone. It is not a shape that happens. Woods do not have rectangles in them, and if they did there would be something in the LiDAR, and I have been through that data at every setting there is.
There is nothing under it. The ground is the ground.
I went back in with the meter on the first ordinary morning after the March window closed, and stood in the middle of it, in a rectangle of wood the size of a large field, in April, at half past five in the morning, and the meter said thirty-nine.
And I stood there long enough to be sure of what I was hearing, which was nothing at all, and then a long way off to the north, outside it, the whole wood singing.