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".
The zoo staff realized that both Roy and Silo were male and conducted additional tests by replacing a rock with a stone and plaster dummy egg. The egg "incubated well", prompting the zookeepers to give them an extra egg from a penguin couple who had previously been unable to hatch two eggs at once simultaneously. Roy and Silo incubated the egg for 34 days and raised the healthy chick, which was female and named "Tango".