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. Audubon wrote that two of his banded phoebe chicks came back to nest near their birthplace. Modern studies doubt it: in one large Indiana study, only 218 of 11,847 banded phoebe nestlings, or 1.8 percent, returned to the study area. In the United States today, a person needs a federal permit to band or mark wild birds, and 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. Great tits readily use nest boxes and nest close together. They do not travel far from where they hatched, and they cope well with being watched. In 75 years, researchers have monitored every nesting attempt and identified every parent and chick, across more than 55 generations. The data showed there is a best number of eggs for a great tit to lay, which depends on how much food, such as caterpillars, is around when the chicks need feeding.

The Amboseli Baboon Research Project in Kenya has followed individually known baboons from birth through their whole lives since 1971. To follow young salmon, scientists tag wild Chinook parr in up to 15 Idaho streams with tiny PIT tags, then detect them at monitoring sites and dams as they swim downstream. Young Chinook in freshwater have dark marks on their sides called parr marks, which help camouflage them. Before they go to sea they lose the marks and grow a dark back and light belly like other open-water fish.

In a drone study of humpback whales, calves grew in body volume by nearly 395 percent and in length by almost 60 percent over six months, while their nursing mothers shrank in body volume by about 17 percent. The energy humpback mothers use to make milk is huge: in Hawaii, the energy a mother spent nursing was more than the whole energy cost of carrying her calf for a year, and mothers lose about a fifth of their body volume over 60 days of nursing. A blue whale calf is about 23 feet long when it is born, and it is weaned at about six months old, when it is over 52 feet long.

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. Scientists call chicks that hatch well developed and ready to move precocial, and most chickens, ducks and turkeys are precocial. Chicks that hatch helpless and stay in the nest are called altricial. Birds born in open country hatch ready to run, and being able to move right away helps them avoid predators.

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 why cubs are born so small. 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.

The skin of an emperor penguin dad's brood pouch is full of nerves that sense temperature, so he can feel the temperature of the egg. 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. A chick needs about 42 kilograms (93 pounds) of food from each parent.

In places with many lions and other predators, half or more of newborn giraffes may die in their first days or weeks. A newborn giraffe's nervous system is ready at birth, like that of a one-year-old human child ready to walk. Only about one in 1,000 to one in 10,000 sea turtle hatchlings is estimated to survive to adulthood. A mother sea turtle does not stay to care for her eggs, and when the first hatchling breaks free and digs, the movement sends vibrations through the nest, and the others begin to dig out too. Hatchlings find the sea by the slope of the beach and by the moon or starlight shining on the water. Many years later, a grown female usually returns to lay her own eggs on a beach near where she hatched.

A single frog can lay up to 20,000 eggs at once, but only a small percentage of the eggs survive to adulthood. Bullfrog tadpoles may take several years to turn into frogs. 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. As a tadpole changes into a frog, it grows lungs and loses its gills, so it can breathe air. Its tail is not shed. The body slowly absorbs it and uses it as a source of energy. Frogs are indicators of ecosystem health: changes in the timing or success of any life stage can signal wider environmental pressures.

Words to know

• banding: ring tagging
• imprinting: early following
• generations: family stages
• incubator: egg warmer
• precocial: ready at birth