Surface density of contaminating sources at redshifts z ~ 2–4. The surface densities are extremely low. Only ~0.4 sources are expected per WFC3/IR pointing. The rapid disappearance of such sources beyond H _{160, AB} 26, almost 1 mag brighter than the detection limits of our shallow fields from ERS and CANDELS, suggests that such sources may have a peaked LF at the wavelengths of interest in these surveys and so could be less of a problem for contamination for fainter z ~ 10 galaxy samples.