Bifurcation at Complex Instability

The properties of motion close to the transition of a stable family of periodic orbits to complex instability is investigated with two symplectic 4D mappings, natural extensions of the standard mapping. As for the other types of instabilities new families of periodic orbits may bifurcate at the transition; but, more generally, families of {\sl isolated invariant curves} bifurcate, similar to but distinct from a Hopf bifurcation. The evolution of the stable invariant curves and their bifurcations are described.