The kiwi lays a very large egg, which gestates for 78 days on average (compared with a chicken’s 21 days)
The chick hatches fully developed, with its eyes open and ready to forage for itself. It has a belly full of yolk, which it can live off for several weeks. This may be a result of evolving in an environment with no land-based predators but plenty of flying ones. The ability to move and eat independently could have been important for survival.
Look at a kiwi egg (on the left) compared with an ostrich egg. The largest adult kiwi weighs 3.5 kg. A female adult ostrich weighs 100 kg. Despite an adult ostrich weighing 30 times as much as an adult kiwi, the kiwi egg is about half the size of the ostrich egg.
A kiwi egg can weigh 25% of the mother’s body weight. For a human, the equivalent would be a 15 kg baby!
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