When the zoo staff realized that Roy and Silo were both male, they tested them further by replacing the rock with a dummy egg made of stone and plaster. As it was "incubated real well", it occurred to the zoo keepers to give them the second egg of a penguin couple, a couple which previously had been unable to successfully hatch two eggs at a time. Roy and Silo incubated the egg for 34 days and spent two and a half months raising the healthy young chick, a female named "Tango".
When the zoo staff discovered that Roy and Silo were both male, they conducted further tests by substituting a stone and plaster dummy egg for the rock. Since it "incubated well", the zookeepers decided to provide them with an additional egg from a penguin couple who had previously failed to successfully hatch two eggs at once. Roy and Silo incubated the egg for 34 days and nurtured the healthy chick, which was female and named "Tango".