Pterodroma arminjoniana
herald petrel
(Also: Trindade petrel)

Herald petrels are found in several, disjunct regions. The subspecies P. a. arminjoniana occurs in the south Atlantic near Trinidade and Martin Vaz Islands and in the Indian Ocean at Round Island in Mauritius. Some authorities do not place the Round Island populations in this subspecies, however. The subspecies P. a. heraldica is found in the southern Pacific, from northeastern Australia and throughout the tropical Pacific to Eastern Island. (del Hoyo, et al., 1992)

Herald petrels are found in the open ocean, only coming near or to land during breeding season near breeding colonies. They breed on oceanic islands or "stacks," on rocky cliffs or ledges up to 1000 meters high. They nest sometimes in dense vegetation on these islands. (del Hoyo, et al., 1992)

Herald petrels are from 35 to 39 cm long, about 318 g, and with wingspans of 88 to 102 cm. This species exhibits color polymorphism, with dark, light, and intermediate forms. Color morphs are similar in appearance to Kermadec petrels (Pterodroma neglecta), but with a pointed tail and more white on the underwing. Light morphs are similar to mottled petrels (Pterodroma inexpectata) because the patterns on their underwings form a loose, dark "M" shape of black patterns against a light underwing. Light morphs have less white on their faces than other Pterodroma species with white faces. Juveniles are similar to adults in appearance. They have pink legs and feet, with black distal portions to the feet, but the legs and feet may be entirely black in dark morphs. Their bills are black. Western south Atlantic populations (Trinidade petresl, P. a. arminjoniana) and Round Island petrels are larger than Pacific forms (P. a. heraldi). (Brooke, 2004; del Hoyo, et al., 1992)

Mated herald petrels cooperate to raise their young, remaining together for at least a breeding season. Otherwise, there is little know about mating systems in herald petrels. (Brooke, 2004)

Breeding season in herald petrels varies substantially across their range. They form loose colonies that are visited throughout the year by adults. Some breeding may occur throughout the year, with peak laying activity in October and April. They nest on the ground or in crevices under rocks. Females lay 1 egg that is incubated for 53 days. Young are fledged at about 100 days old. (Brooke, 2004; del Hoyo, et al., 1992)

Both parents incubate the egg and feed the young. They alternate incubation shifts of about 8 to 9 days long. Hatchlings are fed most frequently in their first 10 days, then less frequently through 75 days old, and much less frequently after that. Young are fed up to 138 grams of regurgitate at a feeding. (Brooke, 2004)

There is no information on lifespan in herald petrels. Other petrel species (Pterodroma) can live up to 20 years, herald petrels are probably similar. (Brooke, 2004)

Herald petrels are active during the day, seemingly foraging mostly during the morning when at breeding colonies. They are found at high densities at breeding colonies. Little is known of their behavior outside of breeding colonies. (Brooke, 2004)

There is no information on home range in herald petrels, they range widely in search of food, both when breeding and when not at breeding colonies.

Herald petrels are vocal, using calls described as "ki"s, repeated every 10 to 12 seconds. (Brooke, 2004)

The food habits of herald petrels have not been reported, although they have been observed eating squid and may eat primarily squid. They seem to associate with Puffinus pacificus. (del Hoyo, et al., 1992)

Herald petrels are preyed on at nesting colonies by non-native mammalian predators, including feral pigs (Sus scrofa) and cats (Felis catus). They may have bred at lower elevations before being excluded to higher elevations and less accessible areas by these non-native predators. Feral pigs and goats (Capra hirca) have also destroyed vegetation on nesting islands, further restricting nesting opportunities. (BirdLife International, 2009)

It can be assumed that herald petrels are an important part of the pelagic seabird fauna, they seem to associate with Puffinus pacificus. (del Hoyo, et al., 1992)

Herald petrels are important members of their oceanic avian community. Guano from their nesting colonies may be collected for sale.

There are no negative effects of herald petrels on humans.

Herald petrel subspecies have been assessed separately by the IUCN. Pterodroma a. arminjoniana (called Trinidade petrels) is considered vulnerable because populations are limited to several small island groups for breeding and are susceptible to threats to those colonies, such as non-native predators, oil spills, and stochastic events. The Round Island populations are also considered threatened by the Commonwealth environmental law in Australia. Pterodroma a. heraldica has a wider breeding range and is considered "least concern." Many breeding colonies are now protected and non-native predators and grazers on some islands have been eradicated, resulting in improved nesting habitat. (BirdLife International, 2009; del Hoyo, et al., 1992; Department of the Environment and Heritage, 2003)

Herald petrels are also known as Trinidade petrels. The subspecies are sometimes considered separate species and the Indian Ocean population has not been thoroughly assessed and may be a different species. Some authorities recognize 3 species instead of 1: Pterodroma atrata, nesting in the Pitcairn Islands in the south Pacific, Pterodroma arminjoniana in the south Atlantic, and Pterodroma heraldica in the south Pacific. Round Island populations may also be a different species, based on significant variation in mitochondrial DNA and information on morphology and parasitic lice faunas. (Brooke, 2004; del Hoyo, et al., 1992)

Pterodroma arminjoniana is named for an Italian vice-admiral, V.F. Arminjoni. (Brooke, 2004)