A kiwi has the largest egg relative to its body size of any bird - it’s about 20-25% of the animal’s entire weight. That’s like if I gave birth to a 35lb baby. 
Image from the Hall of Birds at The Field Museum.

A kiwi has the largest egg relative to its body size of any bird - it’s about 20-25% of the animal’s entire weight. That’s like if I gave birth to a 35lb baby. 

Image from the Hall of Birds at The Field Museum.