Boundary layer receptivity to pairs of unsteady oblique freestream vortical modes is studied in direct numerical simulation of flow over a flat plate with an elliptic leading edge. The freestream is perturbed by three types of oblique Fourier modes, differing in the magnitude of the three vorticity components. The vortical modes excite steady boundary layer streaks, and the associated receptivity mechanism is nonlinear in the forcing amplitude. Leading edges with two different aspect ratios are considered. It is found that the streak amplitudes obtained are largely unaffected by the leading edge bluntness. Whereas linear receptivity is the predominant mechanism at low forcing frequencies, the nonlinear mechanism becomes important when high-frequency vortices are present in the freestream. Nonlinear receptivity is therefore expected to contribute significantly to the excitation of boundary layer streaks by freestream turbulence.