Which bird lays the largest eggs?

The ostrich, at around 1.5 kilograms - the equivalent of roughly two dozen hen's eggs, and the largest single cell produced by any living animal. Relative to the bird, though, it is small: an ostrich egg is about one per cent of the mother's weight, where a kiwi's is closer to a fifth, which is the proportion that actually deserves the superlative.

The shell is about two millimetres thick and strong enough to stand on, which creates an obvious problem for whatever is inside. The chick has a temporary egg tooth on its beak and takes hours or sometimes days to get out. Cooking one takes over an hour, and getting into it takes a saw.

The largest egg ever laid on Earth belonged to the elephant bird of Madagascar, extinct within the last thousand years - about 10 kilograms, holding some 150 hen's eggs' worth of volume, and near the theoretical maximum for a shell that can still be broken from inside. Intact ones occasionally surface at auction, and one was found in 2018 sitting misidentified in a museum's ordinary collection.