  We study the quasiparticle resonance states near strong impurities in the
mixed state of a d-wave superconductor. These states give rise to zero-bias
peaks in the local density of states, observed in scanning tunneling microscopy
experiments. The field dependence of the peaks is obtained by averaging with
respect to the spatially non-uniform Doppler shifts in the energy of
excitations. The hybridization of the magnetic field-induced nodal
quasiparticles with the impurity resonances results in the suppression and
broadening of the zero-bias peaks. The height of the peaks is found to scale as
\sqrt{Hc2/H}. The magnetic field response of the peaks is shown to be strongly
dependent on the field orientation.
