All it takes is a handful of birdseed to transform any tourist visiting Venice’s historic St. Mark’s Square into a human perch for a fluttering mass of pushy pigeons.But a Venetian pigeon’s life may now be for the birds: A municipal ordinance banning people from feeding them in the square went into effect May 1.Especially ruffled are the 19 vendors licensed to sell birdseed in the square, who are out of a job. “It’s a tradition,” said one vendor who, like most others, declined to give his name. “It’s like removing Rialto or the Bridge of Sighs.”When Venetian officials first voted to outlaw pigeon feeding 11 years ago, the area of St.