I examined vigilance behavior of Mallards (Anas platyrhynchos) feeding in flocks with Greylag Geese (Anser anser) on stubble-fields in northern Germany. I measured scans/min and total scan duration, and I calculated mean scan duration. There was an inverse correlation between group size and scanning for Mallards, but not when geese and Mallards were considered as a combined flock. Mallards did not benefit from the presence of geese in terms of reduced vigilance, and they seemed to adjust their vigilance according only to Mallard flock sizes. Vigilance was higher in the presence of geese and may have been directed towards geese as potential competitors. No differences in vigilance between male and female Mallards were found. In August, when males were in eclipse plumage, they showed reduced vigilance.
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Vol. 75 • No. 4