  We investigate experimentally the influence of a background rotation on the
energy transfers in decaying grid turbulence. The anisotropic energy flux
density, ${\bf F} ({\bf r}) = < \delta {\bf u}\,(\delta {\bf u})^2 >$, where
$\delta {\bf u}$ is the vector velocity increment over separation ${\bf r}$, is
determined for the first time using Particle Image Velocimetry. We show that
rotation induces an anisotropy of the energy flux $\nabla \cdot {\bf F}$, which
leads to an anisotropy growth of the energy distribution $E({\bf r}) = <
(\delta {\bf u})^2 >$, in agreement with the K\'arm\'an-Howarth-Monin equation.
Surprisingly, our results prove that this anisotropy growth is essentially
driven by a nearly radial, but orientation-dependent, energy flux density ${\bf
F} ({\bf r})$.
