Nightjar

The nightjar churrs.

That is the actual technical term and Wren has never found a better one. It is a dry mechanical trill that runs for thirty or forty seconds without a breath, rising and falling, and it does not sound like a bird. People who hear it for the first time reliably describe it as a machine, or a frog, or — twice, in Wren's experience — a fault in the equipment.

She records the Ashen Heath every June and July. Nine summers. Two microphones on the same two posts, same orientation, same gain, from dusk until about two.

The point is the long series. Anyone can record a nightjar; there are excellent recordings. What is hard, and what Wren's nine summers are, is the same square kilometre in the same configuration across nine breeding seasons, because that is what lets you say something about change, and change is the only thing anybody funds.

The 2019 data showed four churring males. 2021 showed six. 2023 showed three, which was worrying, and 2024 showed five, which was a relief and a lesson about small numbers.

This year she has two.

Two is bad. Two is the kind of number you check your equipment over.

The equipment is fine.

She has been going out to the posts every third night, which she does not normally do, because the recorders are autonomous and going out to them is exactly the sort of disturbance the protocol exists to prevent. She knows this. She has done it anyway, six times, and each time she has stood on the heath in the dark for a while and listened with her own ears to two birds where there should be five.

There is nothing wrong with the heath. That is the thing she cannot get past. The habitat survey is good. The bracken management is good. The fire risk is managed and there has been no fire. There is no new road, no new lighting, no change in access.

Five to two, in one season, with no cause.

The thing on the tape

On 14 July, at 00:41, on the north microphone, there is eleven seconds of something Wren cannot identify.

It is not a nightjar. It is not a fox, and she has nine years of fox. It is not a person; she has plenty of person, and people are extremely obvious on a recording, because people cannot walk on heather quietly and do not try.

It is a low irregular sound with no clear periodicity, at the very bottom of the frequency range the mic handles well, and it is present on the north microphone and absent on the south.

The south microphone is four hundred metres away.

Wren has listened to those eleven seconds perhaps two hundred times. She has looked at the spectrogram until the shapes stopped meaning anything. She has sent it, without context, to three colleagues.

Colleague one says: mechanical, probably distant, probably agricultural.

Colleague two says: geological, possibly a settlement of the underlying sand, and has offered to put her in touch with someone.

Colleague three, who is the best field ecologist Wren knows and who is not given to drama, listened to it twice and said: "Where exactly is the north post?"

Wren told her.

Colleague three said, "What's the ground like?"

"Sand over clay. Why?"

"Send me the 2023 files. All of them. North mic only."

That was nine days ago.

Wren has not gone back out to the posts since. She has told herself this is protocol discipline.

The nightjars churr on, both of them, from 22:15 or so, most nights, on the same two territories they have held since June.

She has started noticing that they are not on the north side.

She has gone back through nine years to check whether that means anything, and the honest answer is that in 2016 and 2018 there were also no birds on the north side, and that two data points prove nothing, and that she knows this, and that she has been sleeping badly.

Colleague three's email came this morning.

The subject line is: call me before you go back out there