Most penguins lay two eggs per year but emperor penguins lay only one. After the penguins mate, the mother lays her egg or eggs and soon goes in the ocean to eat. The father and mother take turns keeping the eggs warm, and the chicks warm after hatching. The parent on baby duty has nothing to eat. Parent penguins call to find each other amongst the thousands of birds when they return from the feeding grounds. The time one parent is alone with the eggs or chicks and going hungry may be weeks or months depending on what kind of penguin they are. If one parent does not return, the other must abandon the egg to go and eat. Global warming is a threat to penguins along with other arctic animals.