Lunch With the Ducks

As soon as this guy sat down, a pair of mallards hurried over. They stood expectantly as he unwrapped his sandwich. I assume that this is a regular thing. How did it get started? How long did it take before Mr and Mrs. Mallard learned that he could be counted on to share his midday meal? Does he eat his lunch here every day? Do they ever refuse what they are offered, preferring white to whole wheat or disdaining mustard as opposed to mayonnaise? So many questions, all unanswered.