"Almost all species of the penguins are sexual monomorph.
During fieldwork, the sexe could only be determinated by the characteristic courtship display and the dominating behaviour of male penguins. But such characteristic behaviour is only perceptible during the breeding season.
SLADEN (1978) developed a method to sex penguins. With a speculum of about 10 cm, inclusive a built-in light, he could observe the cloacawall of a penguin. Approximately in the middle of the ventral cloacawall, he located 4 papillae in a male penguin, about ½ cm large. The two middle ones accord to the mouths of both the ureters, where the two outer were the mouths of the sperm ducts. Those two which mark the mouths of the ureters are also found in female penguins, while the outermost papillae here are very rudimentary and certainly much smaller then in male penguins.
In the wall of the cloaca of a female is the mouth of the oviduct clearly visible.
Such research for sexe is already done for adélie (Pygoscelis adeliae), humboldt (Sphensicus humboldtii), african (Spheniscus demersus) and emperor pinguins (Aptenodytes forsteri).
According to SLADEN such research can easily be done, as well as during fieldwork as in zoos."