What’s lighting up the trees in the pics? Is it just the camera flash or is there another light source?
Some birds have almost iridescent feathers — very reflective. Something like a hummingbird has sort of a dangling tri-lobed appearance with its tail fanned out below its body when in hover mode.
So that’s my theory: iridescent hummingbirds congregating in and around the trees reflecting some light source.
Just a generalized source from all around. I've just massaged the exposure of the photo to very high to be able to see anything at all in the picture. If I go any higher the sky gets very blue and blotchy. It's the general glow of the city lights as background. It's definitely not reflective on anything we're seeing. Whatever they are, they are the light source when they light up and when they are bright, they light up the fronds around them to true color green.
These were not hovering, but moving at high speed in the tri-lobed photo. Very high speed, leaving what looked like a light trail.