RMyers wrote in post #18786897
I was there right after Christmas for 3 days. It closed for at least one day because of cold temperatures and snow. The one ranger there was needed to do bird support instead of pulling out people stuck in the snow. Otherwise it would have stayed open. Check the Facebook group too and see if anybody has been recently. Bernardo Refuge to the north is state run and would be open. It had lots sandhill cranes and raptors when we checked it out.
We were there the Thursday & Friday before New Years - just as the snow storm arrived.
That lone Ranger found us and told us to get out, as he was going to lock the gates. We packed up & left Friday rather than Monday.
What a drive across 380! Certainly not something a TX guy is used to. 
To the OP: I called just before we went, and just before the shutdown started. The gal in the visitor center advised me that the park would be open, but w/o an manning by the staff.