We have investigated the dynamics of vortices at subcritical microwave currents in dc magnetic fields (up to 0.8 T) in epitaxial DyBa2Cu3O7-δ (DBCO) thin films. Microwave measurements were performed using microstrip resonators as test vehicles at 4.88 GHz and 9.55 GHz on laser ablated DBCO thin films in the thickness range 1800 3800 Å. Experimental evidence indicates that the peak effect (PE) observed in surface resistance vs temperature (Rs vs T) plots in applied dc magnetic fields up to 0.8 T is primarily due to the extended defects in thinner films (1800 Å) such as twin boundaries at the substrate(LaAlO3)-film interface; whereas, the high density of point defect disorder in thicker (⩾3000 Å) films is responsible for low Rs and high depinning frequency ωp. This has been confirmed by generation of columnar defects using 200 MeV Ag ion irradiation which showed that even thicker DBCO films show PE in Rs after the introduction of columnar defects. Further, DBCO films grown on low-twinned LaAlO3 substrates (which cause low density of substrate-related extended defects in the film) have shown PE only at 9.55 GHz but not at 4.88 GHz. Values of ωp have been calculated from experimental Rs data. ωp vs T plots obtained for the thinner films show a peak which is a result of the peaks in Rs vs T plots of these films at 4.88 GHz and 9.55 GHz.