Their instruments are: violin, accordion, guitar and pipe. In "We Ride!" episode the guitarist plays an electric guitar.
Actually, two of them have names: the violinist is named Lupe and the accordionist is named Señor Flan.
The Mariachi Owls are anthromoprhic bird creatures that resemble the humanoid Burrowing Owls in America. They wear hats and use user their musical instruments: violin, accordion, guitar and pipe.
The Mariachi Owls are the peaceful-hearted creatures who doesn't like to fight villains as well. They ended up being friendly to Rango or not. However, They remain calm and relaxable for themselves.
Throughout the movie, the owls are seen narrating the story to see what Rango is doing whether in trouble or saving the day. Suddenly, they appear in many parts where Rango survives many obstacles and appear near the end of the film about Rango who saved the day and became the hero of the Dirt.