14Apr2016 UTC       click at left for video

Frio & Bracken bats cover at least 40 miles in an hour in this video (link above left).  Mexican free-tailed bats are capable of flying over twice that fast in unassisted flight.  The location of both caves at the edge of the Texas Hill Country (dark grey at top) gives the bats immediate access to the agricultural fields that attract their favorite food, the corn ear-worm moth.
Could be as many as ~8 million at Bracken and ~6 at Frio, and this is just a snapshot in time, not the whole emergence!
Stuart bat cave and then Rucker emerge later at top left of video.