  We derive uniform approximations for contributions to Gutzwiller's
periodic-orbit sum for the spectral density which are valid close to
bifurcations of periodic orbits in systems with mixed phase space. There,
orbits lie close together and give collective contributions, while the
individual contributions of Gutzwiller's type would diverge at the bifurcation.
New results for the tangent, the period doubling and the period tripling
bifurcation are given. They are obtained by going beyond the local
approximation and including higher order terms in the normal form of the
action. The uniform approximations obtained are tested on the kicked top and
are found to be in excellent agreement with exact quantum results.
