Why do birds do this?
When I drive home on the highway, I see at least 5 groups of birds just flying surrounded by circles. I would say there were 40 birds contained by each group, one large bird in respectively group and the rest are small, and they form a swarm like thing, why is this?
It's migratory behavior.
Well if it's going dark they are waiting for the other birds to entrap up so they can all go to bed.
Kind of sweat, Isn't it!
Answers: If it's at dusk, there's a likelihood that the birds are feed on bugs. They have a tendency of hovering around contained by an area for that. They need to get as much protein as possible to stir through the night.
I frequently see hummingbirds doing this at dusk (though they don't flock) and we have swifts who exhibit precisely this kind of behavior that you are observe at dusk. Don't know about if one is larger or not, but I think this is more in the order of feeding than anything else.
