  The behavior of a colloidal suspension of rod-like {\it fd} viruses in the
nematic phase, subjected to steady state and transient shear flows is studied.
The monodisperse nature of these rods combined with relatively small textural
contribution to the overall stress make this a suitable model system to
investigate the effects of flow on the non-equilibrium phase diagram. Transient
rheological experiments are used to determine the critical shear rates at which
director tumbling, wagging and flow-aligning occurs. The present model system
enables us to study the effect of rod concentration on these transitions. The
results are in quantitatively agreement with the Doi-Edwards-Hess model.
Moreover, we observe that there is a strong connection between the dynamic
transitions and structure formation, which is not incorporated in theory.
