Are herons predators of ducks?
I never heard of them eating other birds.
shareMe neither. I often kayak in a local creek. Lots of herons and ducks, never seen them fighting.
Got curious and looked up Great blue heron in wikipedia. Under diet there's a large paragraph about what kind of fish they eat, another paragraph about amphibians and rodents.
At the end they note "Though not often, birds such as black rails (Laterallus jamaicensis), phalaropes, American dippers (Cinclus mexicanus), pied-billed grebes (Podilymbus podiceps) and chicks of marsh terns (Chlidonias) are also taken.". I think these birds are generally half the size or less than mallards. So even if herons wanted to, they probably couldn't reliably fight and kill an adult duck.
Probably either director/writer/producer thought herons would be interesting animals to include in the movie, and it would be boring if there were no conflict involved-