[Buincchotourbss]

Also what would make them fly down here ??

Most likely explanation is they are following food sources plants, invertebrates and frogs, that are associated with the rains, you have had plenty of over east.
Population estimates would also be difficult on animals that are mobile and spread over such a large range, would need to get a widespread population estimate over a short period, best way may be using aircraft similar to Kangaroo and Camel estimates (though these are questioned or questionable as well). Overall populations would most likely fluctuate greatly depending seasons.