As they fly over you can hear them squeak and make a pig like grunting sound. Very amusing and umistakeable.
Being crepuscular, they are most active around dusk and dawn. They are easy to see with the binoculars in low light, but this obviously doesn't make it easy to photograph.
I'd been out a number of times just to watch them, but I thought I'd see if I could manage anything at all with the camera. No would be the answer, bar some silhouette shots. These will have to do. It's a near impossible task. Just being able to watch and listen to them more than makes up for it though.
You can just make out the eye of this bird.