Bluecat
I think it's stretching things a bit to assume that a 2 year old chasing pigeons is likely to grow up to chase or mistreat birds and other wildlife. Think of the other crazy things that 2 year olds do - put random objects in their mouths, draw on the walls, have a tantrum in the supermarket... Do you honestly think they'll keep doing those things when they're older? So why shouldn't they grow out of chasing anything that moves, including pigeons?
I agree.
Highly unlikely they’d continue, especially since as they get older they’d understand your explanation of why not.
I’d probably distract him/her at that age, especially if other children are there and doing it too.
Interesting reading the confusing answers on here, about when and where it is OK to chase e.g. OK if it’s inconveniencing us, not OK under other circumstances.