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To simulate the condition of waterfowl nests during the laying period, the authors followed the history of 128 artificial nests that varied in visibility. Among these nests, success in avoiding egg loss to birds was directly correlated with the presence of overhead cover. However, even among those nests that were completely screened by vegetation, 34% were lost. It seemed obvious to the authors that egg-eating birds were reacting to other visual cues such as disturbed vegetation or nest markers left at and around the nests. Disturbed vegetation is much more likely to be the visual cue used by the predatory birds, because, in spite of all efforts to the contrary, it was impossible to approach and leave nest sites, particularly in dense vegetation, without leaving some vegetation disturbed.