El cucuy has roots deep in border folklore

Its name is whispered in hushed tones. For mothers, it is the ultimate threat that keeps their sons and daughters in line. For children, it is the bogeyman, the closet monster and their worst nightmares rolled into one hideous being.

It is el cucuy.

Good article about the Latino boogeyman. Also contains a reference to the Texas "Big Bird" sightings of the 1970s. For more on the Big Birds see here.