I had no idea what type of cloud this was but, luckily, one of my fellow local birders is much more knowledgeable about such things. Peter wrote: ‘I think they’re fall streaks from a contrail where ice crystals drop out of the cloud and get drifted by the winds aloft. Normally seen dropping from cirrus or other high-level clouds.’

As the cloud drifted overhead, it came to look more and more like a magnificent gigantic feather. (The photo below was taken with my phone, which is why the colours look a bit different from the photo above.)