With a mutual inductance method we have measured the temperature dependence of the complex AC impedance Z = R + iωL of high quality YBa2Cu3O7 wire networks. In a perpendicular magnetic field the real and the imaginary part of Z exhibit oscillations resulting from flux quantization in the loops of the network. The relative amplitude of the oscillations of the inverse effective sheet inductance 1/L is consistent with a model where 1/L is renormalized by thermally activated vortex motion.