  We present experimental observations of an anomaly in the coupled response of
auto-parametrically excited microelectromechanical beams. When one of the two
coupled beams is driven at elevated amplitudes, the excitation of dominant and
recessive modes is observed in the driven and non-driven beams respectively.
This anomalous nature of auto-parametric excitation has been unexplored by both
theory and experiments and falls outside the scope of the conventional
description of parametric resonance.
