Behavior and Threat Profile
Mallards and related species are everywhere near standing or slow-moving freshwater. Parks, canal margins, roadside ditches with enough water in them. In Leonida they occupy every available freshwater niche in the same way they occupy every available freshwater niche in the real world.
As game birds they are the accessible entry point for hunting mechanics. Not elusive, not dangerous, present in high density near water. They flush on approach and relocate across the water rather than onto land.
In urban contexts they have the usual urban-duck relationship with humans: they expect food, they approach on foot if someone is standing near the water, and they are almost completely unafraid of human proximity. That behaviour translates directly into Vice City's park pond populations.