The two male chinstrap penguins had found each other in the big city. They had remained faithful. They had even raised a child. But then, not too long ago, they lost their home. Silo’s eye began to wander, and last spring he forsook his partner of six years at the Central Park Zoo and took up with a female from California named Scrappy. Of late, Roy has been seen alone, in a corner, staring at a wall.