Henderson Petrel
Pterodroma atrata
Procellariiformes Order - Procellariidae Family
INTRODUCTION:
The Henderson Petrel is endemic to Henderson Island (Pitcairn Islands group), a remote island in the South Pacific Ocean. It also breeds on Easter Island, and probably on some islands in French Polynesia.
It is found in dense forested areas where it breeds, and it forages over the oceanic waters. It feeds mainly on squid and other cephalopods, fish and crustaceans.
This species is pelagic and wanders widely over the Pacific Ocean, reaching the coasts of South America, especially the coasts of Chile.
The Henderson Petrel nests in a burrow or a crevice on the ground. Both parents share all the nesting duties, until the young petrel becomes independent from the adults, about 100-120 days after hatching.
The Henderson Petrel has a very restricted range, and the population is threatened by predation by rats, involving heavy chick mortality on Henderson Island. In addition, the breeding habitat may be affected by changing sea-levels.
The Henderson Petrel is currently listed as Endangered.
DESCRIPTION OF THE BIRD:
Biometrics:
Length: 36-37 cm
Wingspan: 90-97 cm
Weight: 320 gr at fledging
The Henderson Petrel is a medium-sized gadfly petrel with long, thin wings and body and short tail.
The plumage is almost entirely blackish-grey to bluish grey-brown, sometimes with sooty appearance, depending on moult period and angle of lighting.
The upperparts are mainly blackish, sometimes showing contrasting greyer and browner feathers.
The underparts are uniformly paler grey-brown, but somewhat paler than the upperparts, with soft, whitish scaling on the belly.
Depending on the season, the underwing sometimes shows a contrast between the darker wing linings and the silvery flight-feathers. We can also see a pale grey or whitish stripe on the inner wing, along the leading edge. Depending on the lighting, the underwing appears sometimes mottled black-and-white.
The head is dark brown, with a contrasting pale face mask. The chin is paler, mostly greyish-white.
The bill is black with slightly hooked tip.
The eyes are dark brown.
Legs and feet are pink, but the outer parts of the feet are black.
Male and female are similar in plumage colour and size.
The juvenile resembles adults with general brown and grey coloration. But it may show a slightly paler plumage, with more conspicuous barring on feathers.
The bill is shorter than in adults, but it grows longer and more hooked with the age.
RANGE:
The Henderson Petrel is endemic to Henderson Island (Pitcairn Islands) where it breeds. This remote island is located in the South Pacific Ocean.
It was recently recorded nesting on Easter Island, and possibly on some islands of French Polynesia, W of Pitcairn Islands.
During the non-breeding period, it reaches the coasts of Chile in South America, and wanders over vast areas while foraging.
HABITAT:
The Henderson Island where this species is breeding is a remote, uninhabited island with subtropical climate. The habitat includes dense forest canopies and limestone areas.
The Henderson Petrel breeds in scrub in the dense forest covering the plateau of the island.
However, the Henderson Island is affected by continued accumulation of plastic debris on the beaches, but the main problem is primarily the predation by rats.
CALLS AND SONGS: SOUNDS BY XENO-CANTO
The Henderson Petrel is usually more vocal at breeding sites where it produces low growls and short calls.
Moaning and bleating calls are also given in series that increase in speed and pitch, and then becoming a chatter uttered both in flight and on the ground. It is described as “kyek-kyek-kyek” and lasts several seconds.
BEHAVIOUR IN THE WILD:
The Henderson Petrel is an opportunistic feeder. It feeds primarily on fish, squid and various marine invertebrates. However, it also scavenges for carrion at any available food sources within its habitat.
The marine prey are caught with the sharp bill, both at water surface and underwater. The bird uses its keen eyesight to detect and locate prey underwater. It soars over the ocean, and dives to catch the detected prey.
The Henderson Petrels are often seen flying and gliding near schools of fish, but also over areas where squid congregates at water surface. It primarily forages and feeds at night.
During the breeding season, the Henderson Petrel performs beautiful courtship displays such as aerial acrobatics accompanied by calls often heard during the mating period. The monogamous pair performs synchronized flight patterns to strengthen the pair-bonds.
The Henderson Petrels nest in colonies where their social behaviour promotes group defence against predators.
This species nests in excavated burrows or natural crevices on the ground, under the protection of the forest. Both adults share all the nesting duties.
Following the breeding season, the Henderson Petrel probably disperses widely across the South Pacific Ocean. It may wander over large areas while foraging, usually within subtropical and tropical oceanic waters.
It is recorded off Chile coasts, and sometimes reaches the coasts of Middle America.
The Henderson Petrel is known for its ability to sleep while flying, allowing the bird to rest during long, foraging flights.
The wings of this species are long and narrow, very well adapted for soaring and gliding over the open oceanic waters. It may fly over long distances without landing for incredible durations. It is a pelagic species.
REPRODUCTION OF THIS SPECIES:
The breeding season on Henderson Island occurs mainly between May and December, with peak in June-July. The Henderson Petrel breeds in colonies usually densely packed, involving some interactions among the birds.
This species nests in a burrow excavated in the ground, in an area protected from strong winds and predators. The nest-site is placed in moist subtropical scrub, on top plateau of the island.
However, on Easter Island, the nest is a small depression on the ground, made with some dry grasses and twigs, placed among grasses or in a natural rock crevice shaded by vegetation.
The female lays a single egg, and both adults share the incubation by taking regular turns, during 50-55 days. At hatching, the chick is covered in soft, slate grey down. It depends on adults for food and protection. It is fed by regurgitation.
The chick grows slowly but the flight-feathers develop within a few weeks. It leaves the burrow around 70-80 days after hatching, but it remains in the surroundings.
It usually becomes independent from its parents about 100-120 days after hatching. It is able to perform a sustained flight and to feed on its own.
Following a significant amount of time at sea, the young bird will return to Henderson Islands 5-7 years later as an adult to breed.
PROTECTION / THREATS / STATUS:
The Henderson Petrel is affected and still threatened by predation by rats. An eradication attempt in 2011 failed. The chicks of the species are the main prey of the rats.
The Henderson Petrel is a restricted-range species, and its breeding habitat may be significantly affected by changes in sea-levels and plastic pollution.
The size of the population on Henderson Island was estimated at 19,987 pairs in 2015. This population is suspected to be declining.
The Henderson Petrel is currently listed as Endangered.
Fr: Pétrel de Henderson
Ang: Henderson Petrel
All: Hendersonsturmvogel
Esp: Petrel de La Henderson
Ita: Petrello di Henderson
Nd: Hendersonstormvogel
Sd: hendersonpetrell
Text by Nicole Bouglouan
Sources:
HANDBOOK OF THE BIRDS OF THE WORLD vol 1 by Josep del Hoyo-Andrew Elliot-Jordi Sargatal - Lynx Edicions - ISBN: 8487334105
OISEAUX DE MER – Guide d’identification de Peter Harrison – Editions Broquet (Canada) – ISBN-10 : 2890004090 – ISBN-13 : 978-2890004092
Endemic Henderson Petrels continue to survive in the face of rats
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