Now, I can't verify this. And I have a terrible memory. And I have a habit of convincing myself obviously untrue things are in fact the case. And I can find no verification of this story online. So take it all with a grain of salt.
But I SWEAR that when I was living in Tokyo, I heard the following story reported by the local news:
People living near a train line began to complain of loud bangs on the line as trains went by. Japan Rail officials inspected the line but found nothing untoward. They did not notice any loud noises as trains went by, but as soon as they left, complaints started up again.
It was surmised that somehow local hooligans (they DO have hooligans in Japan, but of course they're very polite hooligans) were getting into the JR right of way and leaving articles on the rails such as pebbles which then made loud noises as the trains went over them.
Bang! And whatnot.
JR posted guards. The noises stopped while the guards were present, but returned again as soon as they left. Nobody could catch the "train-item-bang-makers" in the act, so Japan Rail installed a surveillance camera where the complaints were most common.
And what did they find?
Flocks of crows would gather, perching on streetlights and power cables, chuckling amongst themselves. One would flap down and plant a rock on the tracks, then join his mates. They'd sit and wait. Pretty soon a rushing, roaring JR train comes screaming by and BANG!
The crows all fly up in the air, shrieking and swearing as only crows can, and then settle down. Another of their number (or possibly the same one, crows being tough to distinguish) would flap down again, select another stone, and do it again.
I love crows. What the heck were they doing? Who cares? But check out Joshua Klein's great talk on crows (thanks to Daryl):