SAN BARTOLO MORELOS: For 32 years, Cruz Monroy has walked the streets of a small town on the fringes of Mexico’s capital with a tower of small cages filled with a rainbow of birds. The melodies of red cardinals, green and blue parakeets and multicolored finches fill the days of “pajareros,” or street bird vendors, like him. The act of selling birds in stacks of cages — sometimes far taller than the men who carry them — goes back generations. They’ve long been a fixture in Mexican markets and are among 1.5 million street vendors that work on the streets of Mexico.