What bird and/or animal in Texas makes a whistling sound?

I live in west Texas and have lived here as well as in north central Texas almost my entire life and I thought I was familiar with the sounds of just about every animal and bird in the state until last night. That is when I heard a sound like a loud, steady, shrill whistle that lasted for several seconds. It definitely wasn't human. I'm thinking some kind of bird but if it is it was one that I've never heard before. Does anyone know of any type of nocturnal bird or animal that is native to Texas (or otherwise) that makes such a sound?