Macaroni penguin is a shallow scrape in the ground which may be lined with some pebbles, stones, or grass, or nestled in a clump of tussock grass (on South Georgia Island). Nests are densely packed, ranging from around 66 cm apart in the middle of a colony to 86 cm at the edges. A fertile macaroni penguin will lay two eggs each breeding season. The first egg to be laid weighs , 61–64% the size of the second, and is extremely unlikely to survive. The two eggs together weigh 4.8% of the mother's body weight; the composition of an egg is 20%
Bird egg the shell immediately before laying, but this research shows coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral. In species such as the common guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed. Bird eggshells are diverse. For example: Tiny pores in a bird eggshell allow the embryo to breathe. The domestic hen's egg has around