Walking the North Cornwall coast path not too long ago, saw a guy on a headland who was clearly operating a drone about 400 metres ahead of us, kept eyes on it for ages. Walked onwards to pass him 5 mins later....... turns out he was photographing a Peregrine Falcon hovering and repositioning itself along the cliffs in darting manoeuvres. In fact it might have been 800m ahead or 300m when first spotted. Ranging is not easy without a surface reference point. Just saying.