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Birds start arriving to breed in late July in the northern form, but in October/November in the southern form. Males arrive about a week before females. A clutch of two dimorphic eggs is laid 4.4 days apart. Male and female remain at the nest sharing incubation for the first 12 days or so; thereafter the male takes the first foraging trip and the female the next, both of which last nearly two weeks. In all, males fast for 33 days from arrival, whereas females fast for 39 days from arrival. Most of the first-laid eggs (A-eggs) are lost during incubation, which lasts for 34 days. The few chicks that hatch from A-eggs almost invariably die during the first few days of brooding. The guard stage lasts for 20-26 days. Fledging occurs at 66-73 days.
Crustaceans, in particular euphausids, make up the bulk of food items consumed during most studies of this species. Fish and cephalopods play a minor role, though one study found 53% cephalopods (by mass). Over 90% of the diet of Northern Rockhopper penguins breeding on Gough Island consists of crustaceans (mainly euphausids),with the remaining 10% being made up of fish and, to a very small extent, squid.