[blakestyger]

I've often wondered why birds on the ground in groups, waders on the sea shore, say, start flying about when a raptor like a peregrine flies over.

Surely they're safer on the ground from a bird that hunts by striking its target as it flies - by getting up they are making themselves more vulnerable rather than less, aren't they? The best strategy would seem to be to stay where you are.

[LeeE]

I think it's because the raptor needs to identify a specific target to attack and if the birds stay on the ground they'll be moving much more slowly, making them easier targets to acquire.  Once in the air, not only are they moving much faster, they can all try to flock, making each individual bird even harder to pick out.

[Alan McDougall]

It is easier to avoid attack in a flock than alone

[blakestyger]

It is easier to avoid attack in a flock than alone

They were in a flock both when they were on the ground and airborne - so that isn't the issue.

[Andrew K Fletcher]

Those that adopted the stay on the ground or in the ocean, river and lake defence got eaten and those traits become lost over the generations to those that took to the air. So looking back in time there might have been more land / ocean based predators that instilled the flight rather than fight reaction into each generation. If we see a vehicle heading towards us at speed we tend to jump out of the way too and if we could fly we surely would do so. In that split second we have analysed the threat, determined that we can’t fight it and that standing still is not an option.

What goes on in the birds head must be the same except it probably does not realise that the peregrine in this case requires them to fly in order for it to strike.

A Rabbit on the other hand is a much slower thinker. Sees car headlights, thinks wow that’s a big rabbit, hmm maybe it’s a big fox or could be the farmer with a gun or possibly a poacher erm now let me think about this for a while and gets squidged  between the car and the road surface.  Given sufficient time the rabbit can analyse the threat and eventually realises that the UFO has probably spotted me in thinking mode so I better run.