The wild budgerigar of Australia is a social bird who normally gathers in groups of a few hundred. Ever in search of food and water, often in areas of limited resources, these smaller flocks of insect, grain, and seed-eating parrots become an undulating swarm of thousands… perhaps even millions, as seen in this clip from episode 5 of the BBC’s Earthflight.
Plus, a bit more from budgerigar.com:
Even though budgerigars are typically called parakeets, especially in the United States, they are just one of over 100 species commonly referred to as parakeets, a widely diverse class of tiny, slender parrots spread out over more than a dozen genera in the subfamily Psittacinae of the family Psittacidae…
There are more than five million budgies in the wild today. In the wild, budgies are generally a lot smaller than their captive counterparts. As nomadic birds, they stick to open habitats like scrublands, woodlands and grasslands in dry parts of Australia, and they have inhabited this part of the world for more than five million years. The availability of water and food determines where they go.