Any group of birds, goats, or sheep can be referred to as a flock, but each feathered breed has its own proper title.
Hawks travel in casts, while it’s a bevy of quail, a host of sparrows, and a covey of partridges.
Swans move in herds, and peacocks in musters, while a flock of herons is called a siege.
A group of geese is properly called a gaggle, but only when they’re on the ground.
In the air they are a skein.