Unfortunately no photo because this happens at evening/night and the only light source are street lamps. I'll do my best to describe it.
This is in Corpus Christi Texas and has been going on for a month or two. On a stretch of highway (358) by, HEB, Target, Sam's Club, and other businesses there are thousands of small birds roosting in the trees of the parking lot. I don't see birds of these numbers during the day while I'm coming and going. The most common daytime bird around here are great-tailed grackles, but the birds in the trees are NOT grackles (I take that back, grackles do occupy a few of the trees but not nearly as populated and their calls sound different). I know Starlings gather in huge numbers in many parts and fly in their murmurations but I don't see starlings flying around before coming to land. Also, from the available light they don't look like starlings. They are swallow-like in flight and when in the tree they look like female/juvenile Purple Martins. I know Martins recently migrated and nested but I don't know how long they hang out in the area after fledging nor when the martins migrate away. Also, I have no idea if martins gather like this nor if these gatherings occur at other times of the year. Is there anyone living around here or have something similar going on where you live can help me