Macaroni penguin female are similar in appearance; males tend to be slightly larger. Males also bear relatively larger bills, which average around compared to in females; this feature has been used to tell the sexes apart. Immature birds are distinguished by their smaller size, smaller, duller-brown bill, dark grey chin and throat, and absent or underdeveloped head plumes, often just a scattering of yellow feathers. The crest is fully developed in birds aged three to four years, a year or two before breeding age. Macaroni penguins moult once a year, a process in which they replace all of their old feathers. They
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