When birds first hatch from their eggs, they look quite different from adult birds. Hatchlings are covered in down feathers and their bodies are disproportionately large compared to their heads and wings. Their eyes are closed and they are generally quite helpless, relying on their parents for food, warmth, and protection.
Appearance
The most striking feature of newly hatched birds is their coat of down feathers. Down refers to the soft, fluffy feathers that lie underneath the outer contour feathers. While contour feathers help birds fly and stay waterproof, down feathers provide insulation and warmth. Down feathers lack stiff quills, and instead have soft strands coming off a central shaft. This allows down to “loft” or spread out to trap heat next to a bird’s skin.
In hatchlings, these downy feathers are short, between 0.5-2 cm long depending on the species. They are also sparse, letting the pinkish skin show through. The down is usually a gray, brown, or yellow color that helps camouflage the vulnerable young birds in the nest. The fuzziness of down feathers gives hatchlings an adorable fluffy appearance.
Underneath the down, hatchlings have mostly undeveloped skin. Their flight and contour feathers have not grown in yet. These stiffer, more complex feathers will start growing towards the end of the nestling phase to be ready for the bird’s first flight. Hatchling’s wings are small stubs, making up less than 20% of their eventual adult size.
A hatchling’s body is almost comically oversized compared to its head and wings. Their huge stomachs take up much of their body mass, acting as a built-in food supply. The stomach stores the remaining egg yolk, which nourishes the chick after hatching. The yolk accounts for around 25% of a hatchling’s weight, compared to only 2% of an adult bird’s body weight. As they grow, hatchlings will slim down and develop more proportional body dimensions.
Their necks are short and thin, making a hatchling’s head look especially small. A hatchling’s head accounts for only about 15% of their total body size, versus 25-35% in adults. Their eyes are closed and their bills are soft, limiting their ability to interact with their environment. Hatchlings are born deaf and blind, though their senses rapidly develop within the first weeks.
Helplessness
When birds first hatch, they are essentially immobile. Newly hatched birds are called hatchlings or chicks until they develop flight feathers around 2 weeks old. After this, they are referred to as nestlings. Due to their underdeveloped wings and lack of flight feathers, hatchlings cannot fly or even walk or hop very capably.
Their oversized stomachs and short legs make it difficult for hatchlings to stand up without toppling over. They can scoot around a bit by pushing with their small legs and wings, but spend most of their time lying down. Without parental care, hatchlings would be unable to move to find food or warmth.
In addition to immobility, hatchlings have essentially no ability to thermoregulate or feed themselves. Their down coat and incomplete feather development make it hard for them to maintain their body temperature. They depend on the warmth of their parents sitting on the nest and sheltering them with their bodies and wings.
Similarly, hatchlings rely fully on their parents to bring them food. Their eyes and bills are not adept enough to hunt for insects or seeds. Hatchlings have strong begging reflexes to signal to their parents when they need food. Parent birds will often chew up food before feeding it to young hatchlings.
While helpless at birth, hatchlings develop quickly under their parents’ care. Within a couple weeks, their feathers, legs, wings, eyes, and ears will be developed enough for them to start interacting with the world around them.
Variation Among Species
While all hatchlings are underdeveloped compared to adults, some species hatch in a more advanced state than others. The level of maturity when hatching is known as precociality or altriciality.
Precocial species hatch covered in down feathers and with their eyes open. These include species like ducks, chickens, ostriches, and quail. Precocial chicks can feed themselves immediately after hatching, though they still rely on their parents for warmth. Many precocial species can even swim and walk within hours of hatching.
Altricial species, in contrast, hatch naked, blind, and completely dependent on their parents. Examples include owls, woodpeckers, parrots, hawks, and songbirds. Altricial hatchlings are essentially embryos that complete their development outside of the egg. Their eyes open and they grow feathers several days after hatching.
In terms of helplessness, the most altricial hatchlings are those of swifts, nightjars, and some hummingbirds. These chicks hatch naked and with their eyes sealed shut. With almost no ability to lift their heads, they simply lie still in the nest and gape their mouths to be fed.
Some species, like ducks and chickens, fall in the middle of the spectrum. Their hatchlings are covered in down and have partly open eyes, but still rely somewhat on parents for feeding and warmth early on. Overall, the level of maturity depends on the innate capabilities of the species.
Developmental Milestones
Over the next several weeks after hatching, baby birds undergo rapid growth and reach several developmental milestones. Their helplessness at hatching turns into greater mobility, independence, and ability to interact with their environment.
Here is an approximate timeline of the major changes hatchlings undergo:
1-5 days after hatching
- Eyes open fully (in altricial species)
- Begin growing contour feathers
- Ears open
- Legs strengthen enough for standing
5-10 days after hatching
- Wings grow and start developing flight feathers
- Start repeatedly flapping wings
- Grow first true tail feathers
- Ability to thermoregulate improves
10-15 days after hatching
- Covered in juvenile plumage
- Able to hop, walk, or swim short distances
- Begin exploring the area immediately outside the nest
- Parent birds encourage first short flights
The exact timeline varies based on whether the species is precocial or altricial. The initial helplessness, however, rapidly evolves into impressive physical abilities within the first weeks after hatching.
Conclusion
When birds emerge from their eggs, they look like fluffy, feathered balls with giant stomachs. Their disproportionately large abdomen full of yolk, tiny wings, closed eyes, and lack of contour feathers make them almost entirely dependent on parental care. Within their first few weeks of rapid development, they transform into fledgling birds ready to fly and leave the nest.