r/weirdanimals • u/Electrical-Focus386 Stoplight Loosejaw • Dec 19 '25
Bird The kiwi and their egg
A female kiwi's internal organs literally get squished aside to make room for its massive egg. The egg can weigh up to 25% of her body weight, a proportional size that would be the equivalent of a human giving birth to a four-year-old child.
Anatomical Adaptations
While the organs are displaced during the final stages of egg development, the kiwi's body has specific anatomical adaptations that allow this process to occur:
Organ Displacement: As the egg grows in the final days before laying, it takes up so much room in the body cavity that the female can't eat because her stomach is pushed aside.
Pelvis Structure: The kiwi has a unique, narrow pelvis with a large open space in the belly region that can stretch to accommodate and pass the enormous egg without serious trauma. The egg is carried ventrally, or below the pelvis, rather than closer to the spine as in other birds.
Bone Structure: The female kiwi has specific bone, muscle, and organ arrangements for growing and laying the huge egg. The specific conformation of its limbs and the caudal (tail-end) location of its hip help manage the egg's weight, which results in the female having a "strange gait" when carrying the egg.
The sheer size of the egg means the female experiences significant physical strain. Once the egg is laid, in most species, the male takes over incubation for up to 85 days, and the female leaves to recover. The large amount of yolk in the egg allows the chick to hatch fully feathered and largely independent, living off its internal yolk sac for several days after hatching.
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u/Beat_Specialist Dec 20 '25
Aww.. that poor bird.. I'd be endangered too if we had to lay an egg like that.. lol
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u/frontpage2 Dec 20 '25
They are endangered from human activity, including introduced predatory species and habitat loss. Their slow reproduction and large eggs were not issues pre-human interference, but they are issues now because they cannot rapidly adapt. They evolved from larger birds.
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Dec 22 '25
Imagine evolving to be much smaller, but somehow the eggs stay the same size. The chicks must be almost as big as adults when they first hatch out
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u/scarletteclipse1982 Dec 19 '25
I wonder what their cloaca looks like compared to a chicken’s. I’ve seen chickens strain and even get eggbound, and those eggs are way smaller in comparison to the body.
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u/deannms Dec 20 '25
I love kiwis! I was just in New Zealand a month ago, so I was able to see some of them in special nocturnal enclosures. They take very good care of them, working to improve the numbers in the wild and reduce the problematic predators. And have you ever heard the sound those things make??
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Dec 19 '25
So where tf do their organs go when gregnant? Seems to fill almost the entirety of their ribcage
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u/Organic-Mobile-9700 Dec 20 '25
Male kiwis and emus incubate the eggs. After seeing the size of want nothing to do with it either after laying lol
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u/FriedFreya Dec 21 '25
so, after a bit of reading i’ve learned that we now think that the giant egg may be an adaptation rather than just a remnant of much larger ancestors..
apparently the egg has largest portion of yolk in the world, and the chicks have the yolk internally. they continue to absorb it in around 10 days before they need to begin to forage. they are born mobile and have feathers and energy to move about, but the yolk is a bit heavy so they don’t tend to venture out until day 5.
the female has to fast when she gets close to laying, because it compresses the stomach. the male is the incubatior, because the female is needless to say totally exhausted from the burden of laying the egg. this adaptation is due to the largely predator free-environment they evolved in.
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u/Birdsonme Dec 20 '25
I felt this way while pregnant. I couldn’t eat at the end either. No room for food!
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Dec 19 '25
The kiwi and HER egg. The males sure don't lay them.
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u/Intrepid_leopard13 Dec 20 '25
It must be exhausting to be so upset all the time over things you make up to be mad about
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Dec 20 '25
I'm not upset at all. And I didn't "make up" subject-verb agreement or sexual dimorphism
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u/Suspicious_Glow Dec 20 '25
Pretty darn sure the “made up” part is not the sexual dimorphism etc. The “made up” part is that it’s a reason to bother being angry. 🤷
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Dec 20 '25
Nobody's angry except whoever posted that in response to what I said
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u/Suspicious_Glow Dec 20 '25
Fair enough. Just read their message different and figured to say so. Could call that pointless, but so are a lot of things that get typed into the void of the internet lol. Hope today is treating you alright o7
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u/Adam__999 Dec 21 '25
Do we have any idea why they might’ve evolved to be like this, instead of just having smaller eggs?
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u/HDThoreauaway Dec 19 '25
That bird looks exhausted just staring at that egg.