Poor video even by my standards, what's on there are Little Gull.
Last evening was pleasant enough to go look for the bats again, and that we did. However from the platform we saw half a dozen small gulls circling in the gloom just after sunset. Interesting first of all because practically all of the gulls have now left, in fact I couldn't see any others. Secondly their flight was swift and bouncy, tern-like, and on the wing they snatched morsels from the surface of the water just like terns do. Finally, the dark underwing was confirmation, they were Little Gull.
They did laps of the reservoir for about half an hour and then as the very last light was fading they rose higher in the sky and headed off east. One of my best ever local ticks.
Video - Very Distant Little Gull