| Kiwi Eggs - Largest Eggs in proportion to its size The Chicken-sized kiwi lays eggs six times the size of a chicken egg. A couple of days before the egg is laid, it assumes so gigantic proportions that it fills the female's whole body cavity, forcing the bird to fast. It's a huge burden for the kiwi, while developing the egg, it needs to eat three times as much as usual. The kiwi has the largest egg-to-body ratio (1:5) among all birds.
The chicken-sized species that make up the kiwi family Apterygidae exhibit many unusual traits. The wings are tiny and hidden within the soft, hairlike, gray-brown plumage, and the nostrils are located at the tip of the long flexible bill (rather than at the base, as with most birds). The legs are stout and muscular, with a large claw on each of the four toes. Kiwi are solitary and nocturnal; they live in the forests of New Zealand, sleeping in burrows during the day and foraging at night for worms, insects, and berries.
Kiwi eggs are huge with respect to the size of the mother: The female kiwi lays an egg equivalent to 15–20 percent of her body mass. In contrast, ostrich eggs equal a mere 2 percent of the female ostrich's weight, and a newborn human weighs just 5 percent of its mother's weight at birth.
DNA analyses in 1995 and 2003 redefined the kiwi family structure by identifying five distinct species. These are the North Island brown kiwi (Apteryx mantelli); the little spotted kiwi (A. owenii); the great spotted kiwi (A. haastii); the rowi (A. rowi); and the tokoeka kiwi (A. australis). The latter is further divided into numerous subspecies.
Wonder what adaptive advantage this bird gains by producing such a monster egg. The answer lies in the lack of natural predators. No native mammals exist in New Zealand (except for bats) that could prey on them, which is the primary reason for the loss of most of the birds' ability to fly (think of the kakapo or the takahe, all flightless) on the island. The energy necessary to fly is turned over to producing enormous eggs. Not incidentally, the lack of predation allows for the birds to have very low reproduction rates, raising only one chick per season. As a matter of course, the whole agenda is turned upside down by the introduction of invasive species like rats, pigs and feral cats, wreaking havoc in the bird nests and effectively reducing the population size of these wonderful, but hapless birds.
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