Context : It is often argued that young stellar clusters suffer a significant infant mortality that is partly related to the expulsion of dust and gas in their early phases caused by radiation pressure from hot stars and supernovae .
Near-infrared ( J-K ) –M _ { \mathrm { K } } diagrams of young stellar clusters in nearby spiral galaxies show a bi-modal distribution that is consistent with a fast decline of their intrinsic extinction at an early epoch .

Aims : The distinct features in the color-magnitude diagrams ( CMD ) and the fast change of colors for the youngest clusters allow us to place constraints on their early evolutionary phases , including the time scale for the decreasing extinction caused for instance by gas and dust expulsion .

Methods : Monte Carlo simulations of cluster populations were performed using the power-law distribution function g ( M, \tau ) \propto M ^ { \alpha } \tau ^ { \gamma } .
Integrated colors were computed from Starburst99 models .
The simulated near-infrared CMD were compared with those observed for six grand-design , spiral galaxies using statistical goodness-of-fit tests .

Results : The CMDs indicate a significant mortality of young , massive clusters with \gamma = -1.4 \pm 0.5 .
High initial extinction A _ { V } = 8-11 ^ { \mathrm { m } } and strong nebular emission are required to reproduce the bi-modal color distributions of the clusters .
An extended star formation phase of longer than 5 Myr is suggested .
The reduction of the internal extinction of the clusters starts during their active star formation and lasts for a period of 5-10 Myr .

Conclusions :