One way to learn about young birds is to mark them. In the early 1800s, John James Audubon tied thin silver threads to the legs of young Eastern Phoebes at a cave nest in Pennsylvania, and he is probably the first person to band birds in North America. Today, a person needs a federal permit to band or mark wild birds in the United States, and the U.S. Geological Survey's Bird Banding Laboratory runs the program with Canada's wildlife service. Banding data help scientists with bird science, management and conservation.

The Wytham Woods great tit study near Oxford, England is the longest continuous study of an individually marked animal population in the world. It began in 1947, when John Gibb and David Lack put up 100 nest boxes in one part of the woods, and around 1960 it grew to over 1,000 boxes across the whole 385-hectare wood. Scientists chose great tits because they readily use nest boxes, nest close together, do not travel far from where they hatched, and cope well with being watched. Each bird can be marked with its own leg ring and followed all its life.

Another famous study of young birds came from Konrad Lorenz. In the 1930s, Konrad Lorenz showed that birds hatched in an incubator, with no parents around, follow whatever they first see. He got a one-day-old duckling and found that it followed him as if he were its parent, and he called this early following response imprinting. Lorenz shared the 1973 Nobel Prize in Physiology or Medicine with Karl von Frisch and Nikolaas Tinbergen for studying how animals behave.

Animals are born anywhere from helpless to nearly self-sufficient, and scientists place them on a spectrum. Giraffes are at the self-sufficient end. They are precocial, which means they are born ready to move, and a newborn giraffe's nervous system is ready at birth, like that of a one-year-old human child ready to walk. In places with many lions and other predators, half or more of newborn giraffes may die in their first days or weeks.

Giant pandas are born smaller, compared with their mothers, than nearly any other mammal except marsupials, and as of November 2026, scientists still do not know exactly why. Zookeepers think a panda mother's bamboo diet may be part of the answer. Bamboo has few nutrients, so she puts her energy into making rich milk instead of growing a big baby. A newborn weighs only about 1/900th as much as its mother, and she feeds it up to 14 times a day in its first weeks while the cub gains weight fast.

Emperor penguins start their nesting in the dead of winter, because incubating an egg takes around four months, so the chick hatches when there is the most food in the ocean nearby. The skin of a dad's brood pouch is full of nerves that sense temperature, so he can feel the temperature of the egg. In a 48-hour blizzard the whole huddle can drift as much as 200 meters downwind, and dads take turns moving from the cold edge of the huddle to the warm middle. A chick needs about 42 kilograms (93 pounds) of food from each parent.

Sea turtles are a different case. A mother comes ashore at night, digs a nest, lays her eggs, covers them and goes back to the sea, and by the time the hatchlings come out of the nest, she is gone. When the first hatchling breaks free and digs, the movement sends vibrations through the nest, and the others begin to dig out too. Only about one in 1,000 to one in 10,000 hatchlings is estimated to survive to adulthood, and many years later a grown female usually returns to lay her own eggs near where she hatched.

Frogs are another case. A single frog can lay up to 20,000 eggs at once, but only a small percentage of them survive to adulthood. Tadpoles in ponds that are drying up can speed up their change into frogs, or they can delay it, and some frog species skip the swimming tadpole stage and develop into small frogs inside the egg. Frogs are indicators of ecosystem health: changes in the timing or success of any life stage can signal wider environmental pressures.

Marsupials and monotremes grow up in very different ways. A newborn kangaroo latches onto a teat inside the pouch, and the teat swells and holds it in place for about three and a half to four months. A wombat's tiny, underdeveloped baby grows in the pouch for 6 to 10 months. The platypus and the echidna lay eggs. A baby echidna comes out of its egg after about 10 days, blind and hairless, and drinks milk in its mother's pouch for two or three months.

Some young animals depend on their mothers for a very long time. Orangutan babies cling to their mothers as the mothers move through the trees, and the mothers teach them which foods to eat, where to find them, in which trees and in which seasons. Orangutans are weaned at about age six or seven, and a Sumatran orangutan mother may wait at least eight years before she has her next baby.

Words to know

• imprinting: early following
• precocial: ready at birth
• incubator: egg warmer
• monotremes: egg-laying mammals
• conservation: protecting nature