Stejnegers Petrel (Pterodroma longirostris)

Stejnegers Petrel

Subspecies

Genus	Species	subspecies	Region	Range
Pterodroma	longirostris		PO	n, e

Genus

Genus Pterodroma, Pseudobulweria and Aphrodroma are also knwon as the Gadfly Petrels. They vary in size from rather small birds such as the Cookilaria-species, measuring about 26 cm, to the much larger and robust representatives of this group like the White-headed Petrel with an overall length of about 43 cm. Their plumages also vary a great deal from species to species; from completely black to light grey mantles and pure white bellies, and with different color phases within species. One feature shared by all of them is the black bill of which the shape also shows much variation. Some species are extremely rare and restricted to a very limited area, other are abundant and wander widely or have unknown pelagic ranges.
The group of the Gadfly Petrels counts over 35 species, mainly from the Southern Hemisphere. There are three genera: Pterodroma with about 30 species, Pseudobulweria counting four and Aphrodroma with only one. Many authors have tried to classify the large number of species of this group and to determine their relationships. This has resulted in a division in several subgenera and the grouping of several species which are considered to have a more or less close relationship. The taxonomic discussion has not come to an end yet: new species have been added or split recently and probably will be in the near future.

Physical charateristics

Small, typical “M” marked gadfly petrel. Dark grey upperparts with sharp “M” mark. Bold and very dark grey cap and mask, extending to dark grey half collar on upper breast. Dark grey rump and uppertail-coverts. White throat and lower chest/belly. Predominantly white underwing, but black tip and narrow black trailing edge, extending to leading edge with slight thickening at carpal joint. Separated from most other small gadfly petrels by whiter underwing. Cook’s Petrel P. cookii and de Filippi’s Petrel P. defilippiana have paler crown and nape, and outertail feathers that are paler than central feathers. Pycroft’s Petrel P. pycrofti has less extensive dark patch around eye. Juan Fernandez Petrel P. externa is larger, with white on rump and small black carpal patch

wingspan min.:	53	cm	wingspan max.:	66	cm
size min.:	26	cm	size max.:	31	cm
incubation min.:	0	days	incubation max.:	0	days
fledging min.:	0	days	fledging max.:	0	days
broods:	1		eggs min.:	1
			eggs max.:	1

Range

Pacific Ocean : North, East. Pterodroma longirostris breeds on Alejandro Selkirk Island in the Juan Fernandez Islands, Chile.

Habitat

It nests in burrows on slopes in Dicksonia externa fern-forest and adjacent grasslands at elevations of 700-1,1120 m

Reproduction

The breeding season for Stejneger’s petrel begins in November with the birds nesting in colonies, often with the Juan Fernandez 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. Peak hatching occurs during the first half of February, and fledging occurs in early to mid May. 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.

Feeding habits

It feeds in pelagic waters primarily on squid and small fish

Conservation

This species qualifies as Vulnerable owing to its very small breeding range, which renders it susceptible to stochastic events and human impacts. Confirmation that introduced predators are causing a decline may qualify it for uplisting to Critically Endangered.
Predation by feral cats, introduced brown rats Rattus norvegicus9 and house mice Mus mus has been documented and may be causing a population decline. In mixed colonies with P. externa, cats prefer to take the smaller P. longirostris. Introduced goats (c.6,000) are destroying suitable breeding habitat. In 1995, a fire destroyed habitat within part of the colony, although it is not known if the species was nesting in that part of the colony. In 2002, a massive rainstorm caused multiple landslides within the colony, although the effects of this on the species were unquanitified. The species is potentially threatened by climate change because it has a geographically bounded distribution: its altitudinal distribution falls entirely within 2,000 m of the highest mountain top within its range (1,649 m)

Migration

Transequatorial migrant, occurring in subtropical waters off Japan, Jun-Nov; might also be regular off California. Several records from New Zealand suggest widespread dispersal of non-breeders.

Distribution map

Stejnegers Petrel distribution range map

Planet of Birds