I had this thought while watching ducks.
Birds lay eggs and then sit on them to keep them warm until they are ready.
But why? The eggs was already inside them and it’s warm there of course.
Then I thought it may related to mamals with vaginal canal analogy but the eggs does not grow while out.
So the bird could keep it in the lay it’s just when it’s ready.
My last thought is that carrying the eggs is too dangerous for their safety or its hard to move and gather food.
Please explain 🙂
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That is just how they evolved. Having the babies outside the body does create distinct advantages, as there is less damage to the mother caused by a whole creature growing inside.
In humans, for example, the woman’s organs are rearranged to accommodate the growing fetus, then after a period of months, where the woman is increasingly forced to abstain from any sort of helping or caring for herself and others, the infant tears itself out of the body, leading to sometimes permanent damage and sometimes death.
Egg laying avoids a lot of that. The egg is still large but are most often smooth and easily passed. The fetus grows inside the shell, not the body, so the body doesn’t get reshaped. The mother can leave the egg for periods of time to hunt for food or shore up the nest. And there is very few deaths during egg laying.
Even better, if the mother happens to die before the eggs hatch, it is possible to have something else finish hatching the eggs, where in a human, dead mom usually means dead baby.
Birds typically lay clutches of eggs, as in several eggs at once.
Chickens are pretty different because of domestication and breeding for steady egg production.
Wild birds only lay eggs at certain times, and their bodies are not designed to function well with multiple eggs inside them. It would be somewhat equivalent to a person being 9 months pregnant. And momma bird still has to fly around to get food and water.
Plus, laying the eggs in a nest allows for the papa bird to be involved in the incubation process. They can take turns protecting the eggs instead of it all being up to one of them.
At the end of the day, though, it’s just evolution. Birds that do it this way survive, so it just works. For whatever reason. If other ways worked just as well, we’d see them more often. Apparently, they don’t.
One that hasn’t been mentioned yet is that birds usually only lay one egg at a time, taking a day or longer to make the next egg to add to the nest. They usually don’t start sitting on the eggs until they have a full nest, which depending on the species could be as little as one or as many as a dozen. While they may have enough room in their bodies to hold one egg, holding more generally isn’t possible.
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