Quendale, a small farm near the very south-westerly tip of Shetland....
I set the audiomoth (a small, pre-programmable recording device less half the size of a mobile phone, which runs on three double A batteries) and left it lodged in a drystone wall at Quendale, one of our favourite sites (and scene of impressive daytime vismig). Even the two salvageable nights were pretty windy, and my expectations were low. The second night (30th Sep) produced 43 Redwings, Grey Heron, Song Thrush, Blackbird, Common Snipe and Golden Plover in between lengthy periods of distortion from wind interference, but it was the night before - 29th - that really made it worthwhile.
... and the position of the recorder (black arrow), wedged into a drystone wall next to the derelict barn
Redwings, Skylarks, Snipe, Golden Plovers, Curlew, Blackbirds and Oystercatcher were all clocked migrating overnight, and a huge, excitable collection of more than 600 pre-morning-flight calls of Chaffinches and Bramblings around dawn was a lovely bonus. But the commonest species (on number of calls) during the night-time proper - totalling eleven calls, spread between 2307 and 0122hrs?
Yep, Yellow-browed Warbler! Amazing, and totally unexpected. Interestingly, the calls are all very much within the middle period of the night - many hours from either dusk or dawn - and are well spread; specifically, at 2307hrs (three calls), 2314hrs (two calls), 2319hrs (one call), 0003hrs (two calls), 0044hrs (two calls), and 0122hrs (one, very clear and close, call).
There's a small stand of pretty crummy, gnarled sycamores nearby (hence the finches morning-flight calls), but otherwise it's all open ground; and indeed on our visits there during the days, we only ever saw Yellow-browed Warblers - a grand total of two - some distance away, in low vegetation / iris beds in the burn. The last call, especially, sounds very much like the bird was close(r) to the recorder. Perhaps of interest, the drystone wall that housed the recorder itself creates might be described (and used) as a kind of stepping stone flightline between the (substantial) habitat just to the north in e.g. Brake, and the SW tip of the islands.
So - one, two or more birds? All from the Sycamores - unlikely, owing to the distance and the prevailing northerly wind - or from mobile birds, or both? From roosting, or actively migrating bird(s)? Impossible to know, but fascinating to speculate - and the last species I expected to rank as 'commonest' (on number of calls) on that night's nocmig recording....