@Blackbird : 250,000 bats from the Waugh bridge in Houston
Copied from the Bat-watching sites of Tx. "When the first cold fronts start pushing through in late October to mid-November, the Mexican free-tailed bats begin their migration to Mexico for the winter."
There are bats near Stella Roberts Recycle plant. Fite Rd I think. Delores Fenwick nature center had posted something about bat watch earlier this year but I have not seen anything since then. I've seen the bats emerge in Austin and it was awesome.