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That is an evolutionary question. The simple answer is generally considered to be that eggs weight less than fully hatched chicks, and therefore it would make it difficult for a mother bird to fly if she were carrying five chicks instead of five eggs. As for Flightless Birds, if they evolved from birds of flight, then there is no evolutionary reason that they would have become viviparous.
What else can I help you with?
Do birds give birth or lay eggs to live young?
birds lay eggs
Does a moose have live birth or eggs?
born alive only birds lay eggs
Which does not lay eggs the emu the rhea or the kudu?
The kudu does not lay eggs. Kudus are mammals and give birth to live young, while emus and rheas are flightless birds that lay eggs. Mammals typically do not lay eggs, instead, they give birth to live offspring.
Does starfish lay eggs instead of giving live birth?
it lays eggs
How do you identify those birds who lay eggs and those who give birth?
There are no birds that give live birth.One of the characteristics of birds is that they all lay eggs.
What are mammals differ from birds?
Mammals differ from birds as birds lay eggs, and mammals give live birth.
Do birds and reptiles lay eggs?
Yes, birds and reptiles do lay eggs. Some reptiles, however, give birth to live young.
What are some things that mammals do and birds don't?
mammals give live birth and birds lay eggs
How do cockatoos give birth?
The words "give birth" mean producing live young from within the body. NO BIRDS do this. ALL birds lay eggs which develop into live young outside the body.
What bird dont lay eggs but give birth to natural babbys?
All birds lay eggs. No bird gives live birth.
If birds are mammals how come they lay eggs?
Birds are not mammals. Mammals give birth to live young and nurse them with milk from the mother's body. Birds do not give birth to live young and do not feed their babies with their milk. ----
Does a peregrine falcon have live birth?
Falcons are birds, so they hatch from incubated eggs.
