Avian reproduction primarily involves the laying of eggs, which is a characteristic feature of birds. Most species engage in internal fertilization, where the male's sperm fertilizes the female's eggs inside her body. After fertilization, the female lays eggs, which are often incubated in a nest until they hatch. The number of eggs and the incubation period can vary widely among different species. Once the eggs hatch, the young birds, called chicks, are typically dependent on their parents for food and protection. Parental care varies; some species, like penguins, are known for their extensive nurturing, while others, like quail, may leave their chicks to fend for themselves shortly after hatching.