Oh but they definitely do arrive in droves, humans and cattle and sheep!
Think of a B&S Ball, or cattle and sheep arriving at the sales yards/docks.
I refer to 'drove' as my great grandfathers and their fathers etc did (as drovers), when some of them drove many many head of cattle from Texas on the Qld/NSW border down to the sales yards in Melbourne.
However there are no doubt other interpretations.
