A flock was a term for a large group of animals.
In 1996, Henry Starling suggested that Rain Robinson might have detected a flock of geese rather than a UFO. (VOY: "Future's End")
In 2267, Esteban Rodriguez claimed to have seen a whole flock of birds on the Shore Leave Planet. (TOS: "Shore Leave")
In 2373, a hologram of Leonardo da Vinci claimed to see a flock of starlings, among other things, in the lamp light reflecting off a wall. (VOY: "Scorpion")