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Since Feral Pigeon is a “subspecies level” designation, you are likely to get varying answers from the community based on their personal feelings towards subspecies (see Benefit/Significance of Adding Subspecies among other topics).
My two cents: don’t add a Feral Pigeon designation unless you can reasonably rule out all other options. For me, that means only adding the Feral designation for observations in the Americas and Australia. Where other subspecies occur, I would avoid assuming all individuals in the city are specifically Feral Pigeons, even though that is the most likely case.