  Measurements of thermal conductivity (kappa) vs temperature are reported for
a series of Ca_{1-x} La_x MnO_3(0 <= x <= 0.2) specimens. For the undoped
(x=0), G-type antiferromagnetic compound a large enhancement of kappa below the
Neel temperature (T_N ~ 125 K) indicates a strong coupling of heat-carrying
phonons to the spin system. This enhancement exhibits a nonmonotonic behavior
with increasing x and correlates remarkably well with the small ferromagnetic
component of the magnetization reported previously [Neumeier and Cohn, Phys.
Rev. B 61 14319 (2000).] Magnetoelastic polaron formation appears to underly
the behavior of kappa and the magnetization at x <= 0.02.
