So is it really a belly button?
If by belly button you mean a navel, yes.
If you are picturing a human-style innie or outie, not really.
A bird embryo develops inside an egg instead of being attached to a placenta. It still needs a route for nutrients from the yolk sac to enter the body. The place where that connection closes is the navel.
The scar is most obvious around hatching and then fades.
What is the yolk sac?
The yolk is not just food sitting loose in the egg.
As the embryo develops, blood vessels spread over the yolk sac and move nutrients into the growing chick. The yolk helps fuel development before the bird ever takes its first bite of outside food.
Near hatching, remaining yolk is pulled into the chick's abdomen. That reserve can help support the hatchling during its first hours or days.
What happens to the opening when a chick hatches?
It closes.
In a healthy hatchling, the navel area seals as development finishes. A small scar remains, but it becomes much less noticeable as the chick grows and feathers cover the body.
By the time you are watching an adult chickadee, crow, or robin outside, you are not going to spot its belly button through binoculars.
Do chickens have belly buttons?
Yes, in the same basic sense.
Anyone who raises poultry may hear more about the navel because hatcheries pay attention to whether that area has closed properly. A poorly closed navel can be a health concern in a newly hatched chick.
For a healthy adult chicken, though, the tiny scar is not something most people ever notice.
Is a bird's navel from an umbilical cord?
The word umbilical can make this sound more mammalian than it is.
Bird embryos are connected to extra-embryonic membranes and the yolk sac inside the egg. They are not connected to a mother's placenta by a long umbilical cord the way a human fetus is.
So the developmental idea is related: there is a nutrient connection and a navel where it enters the body. The anatomy around it is different.
Do all egg-laying animals have something similar?
Many egg-developing vertebrates have an umbilical or yolk-sac connection during embryonic development.
The details vary among birds, reptiles, and other groups, but the basic problem is the same. A growing embryo needs access to stored nutrients.
Why do adult birds not have obvious belly buttons?
There is no reason for a large external navel to remain.
Once the yolk connection closes, the scar becomes small. Then skin, body shape, down, and adult feathers make it even harder to see.
Humans are unusual in how obvious our navels remain.
Does a belly button tell you a bird's age?
Only at the very beginning.
The navel area can tell poultry professionals something about a newly hatched chick's development and hatch quality. It is not a practical age marker once a wild bird is feathered and growing normally.
For wild birds, plumage, feather wear, eye colour, bill colour, and molt patterns are far more relevant age clues in species where ageing is possible at all.
How is this connected to egg laying?
The navel belongs to the chick, not the mother.
The female builds and lays the egg. If the egg is fertilized and incubation succeeds, an embryo develops inside. The yolk sac then feeds that embryo until the remaining yolk is drawn into the body around hatch time.
Our how do birds lay eggs? page follows the process from ovulation through shell formation.
Frequently asked questions
Can you see a bird's belly button?
You may be able to see the navel area on a very young hatchling. On an adult bird it is normally tiny, healed, and hidden.
Do baby birds have umbilical cords?
They have a connection between the embryo and yolk sac inside the egg, but not a placenta-and-cord arrangement like mammals.
Does the yolk go inside the chick?
Yes. Remaining yolk is drawn into the body near the end of incubation and provides an early energy reserve.
Do robins have belly buttons?
They develop a navel scar just like other birds. You simply are not likely to see it once the bird has grown and feathered.
Keep following the question
Bird development is full of odd little details. Read how do birds lay eggs?, how long do bird eggs take to hatch?, or return to the Bird Facts hub.