Unidentified aerial phenomenon?

So I recently noticed a TV aerial shaking violently. What made it odd was that there was no wind at the time. I looked at trees, bushes and nearby plants but they showed absolutely no movement at all. And that includes trees, in full leaf, that were taller than the roof where the aerial was situated. So what was going on – a paranormal phenomenon perhaps?

Luckily I already knew the cause of the anomalous activity. I had seen the same aerial a few seconds earlier and there was a crow standing on it then. I had then looked away briefly and when I looked back the bird had gone. Clearly, when the bird took off its weight produced the pronounced shaking I saw. If I hadn’t seen the crow I might still be wondering now what the cause was.

OK so this was a trivial incident but it made me think about some anomalous reports. People occasionally come across scenes that appear inexplicable. But what if the explanation is simply some mundane agency, like the crow, that quit the scene just before the witness arrived? A crucial point in all such cases is that the strange scene must be the first thing the witness sees on arrival. So this explanation can only apply to such specific reports.