Henderson Petrel (Pterodroma atrata)

Henderson Petrel

Subspecies

Genus	Species	subspecies	Region	Range
Pterodroma	atrata		PO	se

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

Medium-sized, slight, dark grey-brown, gadfly petrel. Fairly uniform grey-brown plumage, somewhat paler on underparts. Greyer feather tips on forehead and chin give mottled appearance around bill. Underwing shows pale leading edge between carpal joint and body, and some silvery-white at base of primaries. Black bill. Pink legs, with pink feet proximally, black distally. Similar spp. Dark phase Kermadec Petrel P. neglecta slightly bigger, with white primary shafts, and wholly black legs. Murphy’s Petrel P. ultima is a greyer bird. Providence Petrel P. solandri is distinctly larger, and usually has more facial frosting.

wingspan min.:	85	cm	wingspan max.:	100	cm
size min.:	33	cm	size max.:	37	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 : Southeast. Pterodroma atrata is known to breed only on Henderson Island, Pitcairn Islands (to UK), but may have also bred on Pitcairn Island in the past and has apparently become extirpated from Ducie, also in the Pitcairn Islands. It is likely to breed on other islands in the region too, such as the Gambier and Marquesas Islands (French Pacific Oceanlynesia). In 1991-1992, the breeding Pacific Oceanpulation on Henderson was estimated at c.16,000 breeding pairs and it was suggested that the species could be undergoing a long-term decline.

Habitat

On Henderson, it nests exclusively on the plateau, scattered in the dense forest, though nearer to the coast than P. heraldica

Reproduction

Forms loose colonies. Nests in rock revices, on crag ledges or on ground. Clutch size 1 egg (info derived from Herald Petrel species of which is was considered a subspecies).

Feeding habits

Like P. heraldica it may feed predominantly on cephalopods, also taking fish and crustaceans

Conservation

This species qualifies as Endangered as it probably breeds at fewer than five locations (although currently only known from one) and its population is suspected to be declining as a consequence of predation by rats.
Predation by Polynesian rat Rattus exulans is believed to be the main cause of chick mortality on Henderson, although predation by crabs Coenobita spp. is also a possiblity. If it ever bred on Pitcairn, it is likely to have been extirpated there because of predation by feral cats and introduced rats. The species is potentially threatened by climate change because it has a geographically bounded distribution: it is restricted to an island with a maximum altitude of 33 meter.

Migration

No information available

Distribution map

Henderson Petrel distribution range map

Planet of Birds