A high power pellet rifle might help reduce the population.
WalMart sells them. I live in a no-shoot zone, but according
to my local police, these are acceptable for reducing the
population of chipmunks and red squirrels.
A plastic owl doesn't work well for pigeons or seagulls.
They're too smart. Heck, we've got a pair of real bard owls
living in the trees outback, and even THEY don't scare the
doves away. Fortunately, the common carrier pigeon hasn't
made it to the woods of northern Vermont.