IUCN threat status:

Vulnerable (VU)

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Biology

The breeding season for Stejneger's petrel begins in November with the birds nesting in colonies, often with the Juan Fernández petrel (Pterodroma externa). Burrows, 0.5 - 1 meter long, are excavated in the soil by males using their bill and feet. Breeding females lay a single egg each season, with the peak laying period occurring in late November to early December (7). Peak hatching occurs during the first half of February, and fledging occurs in early to mid May (2) (8). When provisioning chicks, adults embark on foraging trips, typically lasting for four to ten days. Thus the chicks typically go for several days at a time without being fed (7). During the breeding season the diet appears to be dominated by squid, with some fish (7). Like all other petrels and closely related albatrosses, Stejneger's petrel has a special digestive system consisting of an upper and lower stomach. Oil is produced from the petrel's diet and stored in the upper stomach. This concentrated, calorie-rich oil acts as a constant source of energy as small amounts trickle into the lower stomach to be absorbed. It is also an efficient means of transporting energy back to the breeding colony, as the oil weighs less than unprocessed prey, where it can be regurgitated to feed the chicks (7) (9). After multiple days spent foraging at sea, the adults return to the colony, calling noisily. Breeding birds return straight to their burrows, whilst non-breeding birds may spend several hours on the surface, sleeping, interacting, and exploring other burrows. Whilst birds are on the surface of the colony, they are most at risk from predation (8). However, they have a form of defence in the sticky and foul-smelling oil produced by the stomach. If threatened, adults and chicks can eject large quantities of the oil, which sticks onto the fur or feathers of a predator. Not only does this make the predator smell awful, the coated fur or feathers lose their insulating and waterproofing properties, which can be fatal (9).

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