"Gay Penguins raise abandoned chick"

"A pair of gay male penguins are raising a chick from an egg abandoned by its parents, officials at a German zoo have said.
Bremerhaven zoo veterinarian Joachim Schoene said the egg was placed in the male penguins' nest after its parents rejected it in late April

The males incubated it for some 30 days before it hatched and have continued to care for it. The chick's gender is not yet known."-- AOL news website

How do they know they are gay penguins?