MacGillivray's prion is a little-known seabird that was long confused with the closely-related broad-billed prion (its nearest relative) and Salvin’s prion. It has been considered a subspecies of both these species, and has bill measurements that are intermediate between the two. For several decades, MacGillivray's prion was considered to be reduced to a few hundred pairs breeding on La Roche Quille, a rock stack off the coast of rat-infested St Paul Island in the southern Indian Ocean. However, around 2014, it was recognised to be breeding in large numbers on Gough Island in the south Atlantic. As it breeds sympatrically with broad-billed prions on Gough Island (but 3 months later) without evidence of hybridisation, this has led to MacGillivray's prion being considered a full species.

MacGillivray's prions began recolonising St Paul Island after ship rats were eradicated there in 1997–99. A tracking study of birds from St Paul Island revealed that four of seven spent the 2018 winter in the Tasman Sea. However, the only museum specimens from New Zealand (1) and Australia (4) identified in a 2025 study were all from the more distant Gough Island population.

Identification

All eight prion species are very similar in appearance and behaviour, differing mainly in bill shape and size. All are medium-small seabirds that are blue-grey above and white below, with a blackish ‘M’ across the back from wingtip to wingtip, a black tip to the upper tail, blue-grey bill, and blue legs and feet. MacGillivray's prions have bills that are 16–20 mm wide, which bridges the gap in bill width between broad-billed prion and the slightly smaller Salvin’s prion. MacGillivray's prions from Gough Island typically have bills that are 33–36 mm long, compared to 29–34 mm on St Paul Island.

Voice: prions rarely call at sea, but they are vocal on the ground at night at their breeding colonies, giving harsh chattering calls and softer dove-like crooning.

Similar species: MacGillivray’s prion is most similar in bill structure to Salvin prion, and the two have very similar plumage. The main character used to distinguish them in the hand are that MacGillivray’s prion generally has a slightly wider bill (16–20 mm wide, cf. 14–18 mm in Salvin’s prion). MacGillivray’s prions from St Paul Island have bill lengths that overlap considerably with Salvin’s prions. It is likely that genetic methods will be required to confirm the presence of  MacGillivray’s prions from St Paul Island in New Zealand (as indicated by geolocator sensor tracking).

Distribution and habitat

MacGillivray’s prions breed near the Subtropical Front on St Paul Island (820 ha) and the adjacent La Roche Quille (0.7 ha) in the southern Indian Ocean, about 3000 km south-west of Australia, and also on Gough Island (6500 ha) in the south Atlantic Ocean.

Failed breeders from Gough Island (eight) all spent the 2015 winter off the coast of Argentina. Of the seven birds successfully tracked from St Paul Island in 2018, three headed west to an area south-east of South Africa, and four were tracked to the Tasman Sea during March to August

The only accepted New Zealand record is a Te Papa specimen (ex Gough Island) that was found dead on Ōtaki Beach, Horowhenua, in July 1954 and identified using genetic methods in 2025. The geolocator tracking study indicated that birds from St Paul Island approached close to the Fiordland coast in 2018.

Population

Fewer than 1000 pairs on St Paul Island plus La Roche Quille, and at least 300,000 pairs on Gough Island.

Threats and conservation

Ship rats and rabbits were eradicated from St Paul Island during 1997–99, allowing prions to recolonise from La Roche Quille 150 metres offshore. Mice remain present, with no evidence of them preying on seabirds at this location. Eradication of Norway rats on 56,600 ha Amsterdam Island (a former MacGillivray’s prion breeding site, 90 km from St Paul Island) was attempted in 2024.

Mice killed 100% of MacGillivray’s prion chicks in a study colony on Gough Island in 2014-15. An attempted mouse eradication on the island in 2021 unfortunately failed. The small size of the St Paul Island population and the ongoing (and extreme) threat of mouse predation on Gough Island both contribute to MacGillivray’s prion having an IUCN threat listing of Critically Endangered.

A vagrant peregrine falcon killed at least 27 adult MacGillivray’s prions on La Roche Quille and St Paul Island in February 1999.

Breeding

MacGillivray’s prions breed in colonies, nesting in burrows or caves. They return to their colonies in late September and lay a single white egg in late November or early December. They breed as monogamous pairs, sharing incubation and chick-rearing, with the young departing in late February and early March.   

Behaviour and ecology

Little is known about MacGillivray’s prion behaviour. They are essentially identical in appearance to other ‘wide-billed’ prion species when at sea, and so our knowledge of their at-sea ecology is based on 15 geolocator-tracked individuals (eight from Gough Island and seven from St Paul Island). During breeding, they foraged within 400 km of their colonies. Between breeding seasons, they foraged and moulted in subtropical and subantarctic seas up to 7550 km from the colony, staying away from land for about 6 months.

Food

MacGillivray’s prions mainly eat small pelagic crustaceans. As with other ‘wide-billed’ prions, these are likely mainly captured by shallow dives or surface-seizing while hydroplaning – facing into the wind with wings extended, and dipping the head and neck into the upper 10 cm of the water column. Lamellae along the edge of the upper mandible are used to filter small prey items out of mouthfuls of sea water.

Websites

BirdLife factsheet

References

Barbraud, C.; Delord, K.; Le Bouard, F.; Harivel, R.; Demay, J.; Chaigne, A.; Micol, T. 2021. Seabird population changes following mammal eradication at oceanic Saint-Paul Island, Indian Ocean. Journal for Nature Conservation 63. doi.org/10.1016/j.jnc.2021.126049

BirdLife International 2022. Pachyptila macgillivrayi. The IUCN Red List of Threatened Species 2022: e.T104062579A198532259. doi.org/10.2305/IUCN.UK.2022-1.RLTS.T104062579A198532259.en. Accessed on 8 April 2025.

Delord, K.; Cherel, Y.; Roy, A.; Bustamante, P.; Swadling, K.M.; Weimerskirch, H.; Bost, C.-A.; Barbraud, C. 2022. At-sea behavioural ecology of the endangered MacGillivray’s prion from Saint Paul Island: combining tracking and stable isotopes. Marine Ecology Progress Series 697: 149–165. doi.org/10.3354/meps14136

Dilley, B.J.; Davies, D.; Bond, A.L.; Ryan, P.G. 2015. Effects of mouse predation on burrowing petrel chicks at Gough Island. Antarctic Science 27: 543–553.

Jiguet, F.; Robert, A.; Micol, T.; Barbraud, C. 2007. Quantifying stochastic and deterministic threats to island seabirds: last endemic prions face extinction from falcon peregrinations. Animal Conservation 10: 245–253.

Jones, C.W.P. 2018. Comparative ecology of Pachyptila species breeding sympatrically at Gough Island. MSc dissertation, University of Cape Town. https://hdl.handle.net/11427/29646

Jones, C.W.; Phillips, R.A.; Grecian, W.J.; Ryan, P.G. 2020. Ecological segregation of two superabundant, morphologically similar, sister seabird taxa breeding in sympatry. Marine Biology 167: 45. doi.org/10.1007/s00227-020-3645-7

Masello, J.F.; Ryan, P.G.; Shepherd, L.D.; Quillfeldt, P.; Cherel, Y.; Tennyson, A.J.D.; Alderman, R.; Calderón, L.; Cole, T.L.; Cuthbert, R.J.; Dilley, B.J.; Massaro, M.; Miskelly, C.M.; Navarro, J.; Phillips, R.A.; Weimerskirch, H.; Moodley, Y. 2022. Independent evolution of intermediate bill widths in a seabird clade. Molecular Genetics and Genomics 297: 183–198. doi.org/10.1007/s00438-021-01845-3

Micol, T.; Jouventin, P. 2002. Eradication of rats and rabbits from Saint-Paul Island, French Southern Territories. Pp. 199–205. In: Veitch, C.R. and Clout, M.N. (Eds). ‘Turning the tide: the eradication of invasive species’. Proceedings of the International Conference on Eradication of Island Invasives. (Gland: Switzerland and Cambridge, UK.)

Miskelly, C.M.; Tennyson, A.J.D.; Horton, P.; Penck, M.; Ryan, P.G.; Barbraud, C.; Delord, K.; Shepherd, L.D. 2025. Hidden in plain sight; DNA sequencing of museum specimens confirms the occurrence of MacGillivray’s prion (Pachyptila macgillivrayi) in Australia and New Zealand. Emu – Austral Ornithology 125: doi.org/10.1080/01584197.2025.2490644

Roux, J.-P.; Mougin, J.-L.; Bartle, J.A. 1986. Le prion de MacGillivray. Données taxonomiques. L’Oiseau et la Revue Française d’Ornithologie 56: 379–383.

Ryan, P.; Bourgeois, K.; Dromzée, S.; Dilley, B. 2014. The occurrence of two bill morphs of prions Pachyptila vittata on Gough Island. Polar Biology 37: 727–735. doi.org/10.1007/s00300-014-1473-2

Tollu, B. 1984. La Quille (Île Saint Paul, Océan Indien), sanctuaire de populations relictes. L’Oiseau et la Revue Française d'Ornithologie 54: 79–85.

Recommended citation

Miskelly, C.M. 2025. MacGillivray’s prion. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz