The dynamics of highly dilute vortex ensembles in YBa2Cu3O7-delta thin films is investigated by low-field (5-90 Oe) ac susceptibility measurements of the dynamical relaxation rate Q. In a film with relatively weak pinning, flux bundling is found to be effective at all temperatures and down to the lowest fields. In a film with stronger pinning, single-vortex creep dominates only for T<20 K, and small bundle creep is fully developed for T>40 K. The behavior of highly separated vortices is hence surprisingly collective in YBa2Cu3O7-delta. Quantum creep is observed below 11 K, and at about 60 K the elastic vortex description breaks down as the importance of plastic creep gradually increases.