Hi all, any ideas on this one? I live in London but behind our house is a whole set of back gardens for us and our neighbors, which run to a small river. I only hear this call when it's dark, and judging by how it moves around with relative ease I'm assuming it's a bird.Play this audio clip
Very short clip so not easy to make a judgement. It doesn't sound like an owl which would be the most likely bird to call at night.
Just a guess but it could be a fox. They have a wide variety of calls. Have a listen to this especially the ones near to the end of the recording to see what you think.