Egg size: 68 ? 48 mm
Incubation lasts for around 55 days. During that time both parents incubate the egg in shifts that last between 3–6 days; the length of shift varies by location, although female shifts are longer than those of males. Birds have been recorded losing between 20–33% of their body mass during a shift.
The chick has no feathers when it hatches and one parent must stay with it at all times to protect it from the sun's heat. After a month the chick will be covered with white down (fluffy baby feathers). The young iwa are fed every 18 hours and stay in the nests for about 145 days after they fledge (grow adult feathers and can fly), they still rely on their parents for about a year.
They reach full adult maturity at 8 to 9 years for females and 10 to 11 years for males and they rarely attempt to breed before aquiring full adult plumage.
They start looking for a mate when they reach maturity. Both sexes have a patch of red skin at the throat that is called the gular sac; in males this is inflated in order to attract a mate. Groups of males sit in bushes and trees and force air into their sac, causing it to inflate over a period of 20 minutes into a large red balloon. While females fly overhead the males waggle their head from side to side, shake their wings and call. Females will observe many groups of males before forming a pair bond.