  We are studying the effects of light dynamical quarks on the excitation
energies of a flux tube between a static quark and antiquark. We report
preliminary results of an analysis of the ground state potential and the
$\Sigma^{\prime+}_g$ and $\Pi_u$ potentials. We have measured these potentials
on closely matched ensembles of gauge configurations, generated in the quenched
approximation and with 2+1 flavors of Asqtad improved staggered quarks.
