The blue petrel is an abundant small seabird of the extreme southern Atlantic and Indian Oceans, with a few hundred pairs breeding in the Pacific sector on Macquarie Island. Although rarely seen in New Zealand seas, large numbers occasionally wash up dead on New Zealand beaches in late winter and spring. A surprising number (13) were found oiled (dead) on Bay of Plenty beaches in October 2011 following the C.V. Rena stranding and oil spill, indicating that blue petrels do occur over inshore waters at times. Maybe the few pelagic seabird watching opportunities in New Zealand are simply at the wrong times and places to see this cryptically coloured seabird with its diagnostic white-tipped tail. It is the only member of the genus Halobaena.
The blue petrel is a small seabird that combines features of prions and the smaller gadfly petrels (genus Pterodoma). Its overall colouration (grey-blue above and white below, including underwing) and flight behaviour are similar to prions, while its bill structure and head plumage are more like a small gadfly petrel (e.g. Gould’s petrel). A conspicuous blackish cap extends to the eye and onto the sides of neck as a partial collar, contrasting with the white forehead and throat, and a curl of white extending up towards the ear. The dark cap blends into the grey-blue upperparts and upperwings. As for prions, a dark open ‘M’ extends across the upperwing from wingtip to wingtip, broken only across the lower back. The tail is square with a unique white tip, readily seen at sea if the dorsal surface is seen. The underparts are white, apart from the dark half-collar. The bill is blackish, and the legs and feet blue with pink webs. Blue petrels mainly fly close to the sea surface; they soar more than most prions, but without the towering arcs of otherwise similar small gadfly petrels (the latter also have darker upperwings, with the ‘M’ not as prominent).
Voice: blue petrels are silent at sea, and give cooing and cackling calls similar to prions at breeding colonies at night.
Similar species: blue petrels are generally similar to the more slender-billed of the prions (e.g. thin-billed prions, fairy prion) and smaller gadfly petrels (e.g. Cook' petrel, Gould's petrel), but the white-tipped tail is completely diagnostic.
Distribution and habitat
The blue petrel is a pelagic, circumpolar seabird of the deep south, common near the pack ice but ranging north to 40° S. They mainly stay near breeding islands during the southern summer, but spread into the Pacific sector in winter and spring. Blue petrels nest in large colonies, burrowing into tussock-covered slopes on islands off southern Chile (Diego Ramirez and Cape Horn Islands) and on South Georgia, and Prince Edward, Crozet and Kerguelen Islands. Smaller numbers nest on Marion and Macquarie Islands.
The global population of blue petrels numbers in the low millions. Major colonies include Diego Ramirez Islands (1,000,000 pairs), Kerguelen Island (100,000–200,000 pairs), Prince Edward Island (100,000 pairs), South Georgia (70,000 pairs), and Crozet Islands (40,000–180,000 pairs). Fewer than 1000 pairs on Macquarie Island. Blue petrels are mainly recorded beach-wrecked in New Zealand, especially during July-October: typically 10–100 per annum, max 881 in 1984. There are 9 records of beach-wrecked blue petrels from the Chatham Islands.
Threats and conservation
Blue petrels are not globally threatened, but introduced cats and rats have devastated some colonies. Cats and ship rats (both since eradicated) confined blue petrels to coastal stacks on Macquarie Island, and ship rats exterminated the population on Possession Island, Crozet Islands. Feral cats (since eradicated) greatly reduced the population on Marion Island, and continue to impact the population on Kerguelen Island. The subantarctic skua and the closely related Chilean skua are the main natural predators.
The blue petrels is a colonial, monogamous burrow-nester. Both sexes incubate the single white egg for 45-49 days, and feed the chick by regurgitation. The chick fledges after 43-60 days. Laying occurs in October, hatching in December, and fledging in February.
Behaviour and ecology
The blue petrel is a pelagic seabird, only coming ashore to breed. At sea it often occurs in single species flocks or in mixed flocks with prions, especially thin-billed prions (Drake Passage), Antarctic prions (near South Georgia and southern Indian Ocean) and Salvin’s prions (southern Indian Ocean). As typical for most small petrels, blue petrels are nocturnal at their breeding sites, nest in burrows in large colonies, are monogamous, and have shared care of the single egg and chick.
Blue petrels mainly eat crustaceans, also small fish and squid obtained by dipping while in flight, or while swimming. They will also dive. Blue petrels often associate with prions, and occasionally attend feeding whales. They usually show little interest in ships, but will fly alongside in the lee of larger vessels.
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- Breeding season
- Egg laying dates