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. Scientists call chicks that hatch helpless and stay in the nest altricial, while they call chicks that hatch well developed and ready to move precocial. Pigeons, songbirds, and owls and eagles are altricial, whereas most chickens, ducks and turkeys are precocial.
Birds born in open country hatch ready to run, and being able to move right away helps them avoid predators. After it makes the first hole in the shell, a chick stops and rests for three to eight hours before it breaks out, and a few hours after hatching it is dry and fluffy and starts to walk around. 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. 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. He wrote that two of his banded phoebe chicks came back to nest near their birthplace, but 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. A bird historian, Matthew Halley, argued that part of Audubon's famous banding story might never have happened, which shows that scientists must check even famous old reports against the evidence. In the United States, a person now needs a federal permit to band or mark wild birds, and the U.S. Geological Survey's Bird Banding Laboratory runs the program with Canada's wildlife service, 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. 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, and each bird can be marked with its own leg ring and followed all its life. In 75 years, researchers have monitored every nesting attempt in the boxes and identified every parent and chick, across more than 55 generations of great tits.
Wytham 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. Long records also show that spring has moved earlier: in 2022 the first great tit egg at Wytham Woods was counted on 28 March, almost exactly a month earlier than 75 years before. The Amboseli Baboon Research Project in Kenya has followed individually known baboons from birth through their whole lives since 1971, and researchers study baboon stress and growth without disturbing the animals by testing hormones in their droppings. 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. These studies estimate how many young Chinook survive from the parr stage to the smolt stage, and how fast they grow and move.
A giraffe mother gives birth standing up, and her newborn calf drops about six and a half feet to the ground. The fall helps break the umbilical cord and starts the calf's first breath. In its first days a calf is often tucked into tall grass while its mother feeds, and she comes back to nurse it. In places with many lions and other predators, half or more of newborn giraffes may die in their first days or weeks.
Only about one in 1,000 to one in 10,000 sea turtle hatchlings is estimated to survive to adulthood, and many years later a grown female usually returns to lay her own eggs on a beach near where she hatched. Sea turtles come out of their nests together: when the first hatchling breaks free and digs, the movement sends vibrations through the nest, and the other hatchlings begin to dig out too, while a mother sea turtle does not stay to care for her eggs, and by the time the hatchlings come out of the nest at night, she is gone.
A single frog can lay up to 20,000 eggs at once, but only a small percentage of the eggs 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. A tadpole's 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.
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 joey spends its first six months relying on the pouch for protection and milk, and then it comes out to learn how to forage and avoid predators. Two kinds of mammals lay eggs, the platypus and the echidna, which are called monotremes. A baby echidna comes out of its egg after about 10 days, blind and hairless, and it then drinks milk in its mother's pouch for two or three months. When it grows prickly spines, its mother takes it out of her pouch and builds a burrow for it.
A monarch caterpillar is less than 1 centimeter long when it hatches, and it grows to about 5 centimeters. It grows to almost 2,000 times the mass it had when it hatched. A monarch egg is about the size of a pinhead or the tip of a pencil. Inside the chrysalis, the caterpillar's chewing mouth changes into the straw-like tongue of a butterfly, used for sipping nectar. The other way insects develop, incomplete metamorphosis, skips the pupa stage and has only three stages: egg, nymph and adult.
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. They 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.
A newborn Asian elephant weighs between 150 and 350 pounds and may stand about three feet tall at birth. It drinks milk with its mouth, so it does not need a long trunk yet, and elephant calves spend their days practicing. They are clumsy with their trunks at first, but they learn.
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. In Hawaii, the energy a mother spent nursing was more than the whole energy cost of carrying her calf for a year. Humpback mothers lose about a fifth of their body volume over 60 days of nursing in Hawaii. A blue whale calf is about 23 feet long when it is born and weighs 5,000 to 6,000 pounds, and the calf is weaned at about six months old, when it is over 52 feet long.
An emperor penguin dad keeps the egg warm on top of his feet, and the skin of his brood pouch is full of nerves that sense temperature, so he can feel the temperature of the egg, while the moms go to sea to feed on fish. In a 48-hour blizzard the whole huddle can drift as much as 200 meters downwind, and the dads take turns moving from the cold edge of the huddle to the warm middle. 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, and a chick needs about 42 kilograms (93 pounds) of food from each parent.
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 panda's pink skin is covered with white fur within about 48 hours, the black markings come next, and the fur is all filled in by about three weeks.
Words to know
- altricial: helpless at birth
- precocial: ready at birth
- imprinting: early following
- monotremes: egg-laying mammals
- generations: family stages
- hormones: body chemical signals
