  Phase response curve is an important tool in studies of stable self-sustained
oscillations; it describes a phase shift under action of an external
perturbation. We consider multistable oscillators with several stable limit
cycles. Under a perturbation, transitions from one oscillating mode to another
one may occur. We define phase transfer curves to describe the phase shifts at
such transitions. This allows for a construction of one-dimensional maps that
characterize periodically kicked multistable oscillators. We show, that these
maps are good approximations of the full dynamics for large periods of forcing.
