  In this paper we report some extraordinary nonlinear dynamics measured in the
resonance curve of NbN superconducting stripline microwave resonators. Among
the nonlinearities observed: aburpt bifurcations in the resonance response at
relatively low input powers, asymmetric resonances, multiple jumps within the
resonance band, resonance frequency drift, frequency hysteresis, hysteresis
loops changing direction and critical coupling phenomenon. Weak links in the
NbN grain structure are hypothesized as the source of the nonlinearities.
