If your talking about vultures it is because they are meat eating birds and they are circling to signal the others that there is meat there or they could be already vultures at the dead animal they found so there waiting for the others to have there fill and fly away so they can land and eat too.
Blackbirds reproduce by laying eggs.
a group of Blackbirds is called a murder
There is no specific collective noun for blackbirds but any collective noun for birds will do; for example a flight of blackbirds or a flock of blackbirds.
Blackbirds
The collective noun for blackbirds could be either a cloud, flock, grind, or a merl of blackbirds.
The blackbirds that have been made already will fly. New ones will not be there. Blackbirds have been discontinued in production.
Do what fly packs or alone?
Blackbirds, including red-winged blackbirds, are an example of black-colored birds that fly together. Grackles, starlings and brown-headed cowbirds also fly together.
BAD COmpany 2? if so then no only Apaches and blackbirds
Wild Turkey
Of course they do. Haven't you seen the beautiful glint of their red wings when they flit around?
No
Blackbirds just born will be able to leave the nest at about 14 days. They will flutter close by remaining in cover and usually be able to fly within a week.
Turkey Vulture tend to fly in "packs" although they are actually called Committees. Black Vulture tend to fly alone or follow Turkey Vulture and steal their finds.
Blackbirds reproduce by laying eggs.
Baby blackbird's are equipped to fly the nest very soon, before they can fly and gather food. They will flop out and become fledglings.
a group of Blackbirds is called a murder