Unidentifiable sound

Unidentifiable sound

Observation - Unidentifiable sound - UK and Ireland. Description: Walking through wet upland pasture and heathland (sample photograph attached), I heard a number of snipe and curlew drumming and calling just on the twilight before darkness.

Walking through wet upland pasture and heathland (sample photograph attached), I heard a number of snipe and curlew drumming and calling just on the twilight before darkness. All of a sudden, there was a completely unexpected sound, and I would love to hear any suggestions as to what it could have been.

The first time I heard it, I thought that a small crow or jackdaw was being killed, but it emerged that it was a deliberate call from a bird moving very quickly around in the darkness, quite low and in a wide circuit.

The sound started with a short and very quiet hiss, being followed by a quick series of loud and grating squeals which went on for three or four seconds, like a cross between the movement of a rusty pulley and the sound of quickly pumping up a bicycle tyre with one of those old portable pumps. It sounded violent to begin with, but looking back, it was more like a display call or something connected to mating.

The call was repeated every three or four minutes from a moving source at various spots across the area, but never further than a couple of hundred yards. Snipe carried on drumming regardless.

We have a variety of waders on the property, and I am very familiar with the calls of curlew, lapwing, snipe, woodcock etc., but this was something I have never heard before, and find it hard to describe.

Any suggestions are very welcome.