  The mechanism of the generation of dark matter and dark radiation from the
evaporation of primordial black holes is very interesting. We consider the case
of Kerr black holes to generalize previous results obtained in the
Schwarzschild case. For dark matter, the results do not change dramatically and
the bounds on warm dark matter apply similarly: in particular, the Kerr case
cannot save the scenario of black hole domination for light dark matter. For
dark radiation, the expectations for $\Delta N_{eff}$ do not change
significantly with respect to the Schwarzschild case, but for an enhancement in
the case of spin 2 particles: in the massless case, however, the projected
experimental sensitivity would be reached only for extremal black holes.
