  Background: Optical potentials are crucial ingredients for the prediction of
nuclear reaction rates needed in simulations of the astrophysical
\gamma-process. Associated uncertainties are particularly large for reactions
involving \alpha-particles. This includes (\gamma,\alpha) reactions which are
of special importance in the \gamma-process. Purpose: The measurement of
(\alpha,n) reactions allows for an optimization of currently used
\alpha-nucleus potentials. The reactions 165Ho(\alpha,n) and 166Er(\alpha,n)
probe the optical model in a mass region where \gamma-process calculations
exhibit an underproduction of p nuclei which is not yet understood. Method: To
investigate the energy-dependent cross sections of the reactions
165Ho(\alpha,n) and 166Er(\alpha,n) close to the reaction threshold,
self-supporting metallic foils were irradiated with \alpha-particles using the
FN tandem Van de Graaff accelerator at University of Notre Dame. The induced
activity was determined afterwards by monitoring the specific \beta-decay
channels. Results: Hauser-Feshbach predictions with a widely used global
\alpha-potential describe the data well at energies where the cross sections
are almost exclusively sensitive to the \alpha-widths. Increasing discrepancies
appear towards the reaction threshold at lower energy. Conclusions: The tested
global \alpha-potential is suitable at energies above 14 MeV, while a
modification seems necessary close to the reaction threshold. Since the \gamma-
and neutron width show non-negligible impact on the predictions, complementary
data are required to judge whether or not the discrepancies found can to be
solely assigned to the \alpha-width.
