Rockhopper penguin reaching full growth, they are about 20 inches in height. Males and females cannot be distinguished just by looks, so a DNA test is conducted by taking a feather from the bird to determine its gender. Like many penguins, rockhopper penguins have a white belly and the rest of their body is black. Some characteristics that differentiate them from the other penguins are their red eyes, orange beak, pink webbed feet, and the yellow and black spiky feathers they have on their head. Although their yellow and black spiky feathers differentiate them from other penguins, rockhopper penguin chicks do not
Bird-of-paradise lek-type mating system. Others, such as the "Cicinnurus" and "Parotia" species, have highly ritualised mating dances. Males are polygamous in the sexually dimorphic species, but monogamous in at least some of the monomorphic species. Hybridisation is frequent in these birds, suggesting the polygamous species of bird of paradise are very closely related despite being in different genera. Many hybrids have been described as new species, and doubt remains regarding whether some forms, such as Rothschild's lobe-billed bird of paradise, are valid. Birds-of-paradise build their nests from soft materials, such as leaves, ferns, and vine tendrils, typically placed in a tree