I know the Birkhoff Ergodic theorem; and I know what is a Riemannian manifold and what a geodesic is.
I also read the definition of geodesic flow on the tangent bundle of one such. But I do not yet know the meaning of the statement "the geodesic flow is ergodic", of course with some added conditions, such as constant negative curvature.
Could someone please give me a reference for me for an introduction to this topic, and how does this ergodicity relate to Birkhoff's ergodic theorem?