  We study what happens to D and D_s mesons as the temperature increases, using
lattice QCD simulations with N_f=2+1 dynamical flavours on anistropic lattices.
We have access to five temperatures in the hadronic phase. Using the determined
groundstate mass at the lowest temperature, we investigate the effect of rising
temperature by analysing ratios of mesonic correlators, without the need for
further fitting or spectral reconstruction. In the pseudoscalar and vector
channels, we demonstrate that temperature effects are at the percent level and
can be captured by a reduction of the groundstate mass as the thermal crossover
is approached. In the axial-vector and scalar channels on the other hand,
temperature effects are prominent throughout the hadronic phase.
