The purpose of this study was to compare two survey protocols for estimating the size of Snow Goose flocks in winter. Compared to photo counts of the same flocks, visual estimates were biased low when flock size exceeded 2000 birds, and the degree of this bias increased with flock size. Correction factors required for visual estimates of flocks with 2000–4000 birds and >4000 birds were approximately 1.4 and 1.6, respectively. These findings have implications for traditional, annual surveys conducted on even larger populations of Snow Geese in other parts of North America and for other more criptic species, such as ducks and shorebirds.