The two similar-looking species of giant petrels, the Northern Giant Petrel Macronectes halli and the Southern Giant Petrel M. giganteus, are renowned for being difficult to identify. In this paper we review and offer new guidelines on identification of these birds at sea, on land, and as dead specimens. Criteria for identifying giant petrels are available in the scientific literature, especially regarding bill-tip coloration which readily differ from one species to another. Plumage characters, although useful to discriminate species, are not adequately covered at present. Thus, for each species we describe in detail and illustrate distinctive age-related plumage stages, or types, from juveniles through to adult breeders. We also comment on giant petrel biometrics, body weight, and some aspects of their behaviour, in order to help ornithologists and birdwatchers separate males and females, and eventually specimens from South America–Gough Island, Antarctic and sub-Antarctic regions.

Giant petrels Macronectes are large Procellariiformes with a wingspan usually in excess of two meters in males, slightly less in females, and are similar in size to Thalassarche mollymawks. They display a wide range of plumages, from dull-black to brownish-grey and even white, according to age and species. The discovery of two distinct populations breeding at Macquarie Island (Australian Antarctic Territory; Figure 1), laying about six weeks apart (Warham 1962), led Bourne & Warham (1966) to restrict the name Macronectes giganteus (Gmelin, 1789) to those birds breeding on Antarctic islands, the Antarctic Peninsula and continent, and on islands of the South Atlantic, and to resurrect the name Macronectes halli Mathews, 1912 for birds breeding on sub- Antarctic islands, from South Georgia through the Indian Ocean to the New Zealand area. Voisin & Bester (1981) and Voisin (1982b) showed later that the form breeding on the Falkland and Gough Islands (South Atlantic), as well as on islands off the Argentine coast, represented a well-marked subspecies: acronectes giganteus solanderi Mathews, 1912, for which Carlos et al. (2005) proposed the vernacular name South Atlantic Giant Petrel. Hereafter, we follow current usage in referring to M. halli as Northern Giant Petrel and M. giganteus as Southern Giant Petrel.

Ringing recoveries and subsequent satellite-tracking studies have shown that both species of giant petrel roam the southern ocean widely, especially immatures, but also adults in the breeding and non-breeding seasons (Hunter 1984; Voisin 1990; Parmalee 1992; Trivelpiece & Trivelpiece 1998; González-Solís et al. 2000a, b; Patterson & Hunter 2000; Patterson & Fraser 2000, 2003; BirdLife International 2004; González-Solís et al. 2008). Antarctic populations of Southern Giant Petrel are especially wide-ranging, and one should not assume that, for example, a Southern Giant Petrel seen off the Argentinean–Brazilian coast at any time of the year is necessarily M. g. solanderi.<>

Recently, Penhallurick & Wink (2004) proposed to re-group M. halli as a subspecies of M. giganteus on the basis of low mitochondrial cytochrome-b gene divergence. Such a position is untenable since both species have long bred sympatrically, and often in close proximity, on South Georgia, Marion, Crozet and Macquarie Islands (Figure 1) without regular interbreeding. A few cases of inter-specific breeding involving male M. giganteus paired to female M. halli have been reported from Marion (Burger 1978; Cooper et al. 2001) and Macquarie Islands (Johnstone 1978), although the resulting eggs did not hatch. Only at South Georgia has occasional hybridisation been reported (Hunter 1982, 1987). Given these circumstances, we can reasonably assume that gene flow between the two species is extremely limited. In birds, many closely related species are known to hybridise regularly, e.g. Anas dabbling ducks (Carboneras 1992), and Common Phylloscopus collybita and Iberian P. ibericus Chiffchaffs (Salomon et al. 2003), without merging into one single species. Even if ‘their apparent failure to interbreed is not quite as straightforward as if they bred at the same time without interbreeding’ (Penhallurick & Wink 2004), M. giganteus and M. halli do not genetically mix.

Several authors have dealt with giant petrel identification, especially of birds at sea (Johnstone 1971, 1974; Conroy et al. 1975; Voisin 1982a; Hunter 1983; Voisin & Teixeira 1998; Jiguet 2000; Shirihai & Jarrett 2002). Here we review, and offer new guidelines on, giant petrel identification at sea, on land, and as dead specimens.

We are grateful to Steve Copsey, Fernanda I. Colabuono and Ronald Saldino for allowing us to use their photographs. Renata F. Cunha kindly prepared Figures 7 & 8. CJC received support from Fundação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil. The typescript benefited from the input of Bernie Zonfrillo, Stephen Hunter, Bill Fraser, an anonymous referee and the editorial advice of Martin Heubeck.

Anonymous, 2002. The oldest stinker in town? Falkland Conservation Newsletter (Sep. 2002): 4.

BirdLife International, 2004. Tracking ocean wanderers: the global distribution of albatrosses and petrels. Results from the Global Procellariiform Tracking Workshop; 2003 September 1-5; Gordon’s Bay, South Africa. BirdLife International, Cambridge, UK.

Bourne, W. R. P. & Warham, J. 1966. Geographical variation in the giant petrels of the genus Macaronectes. Ardea 54: 45–67.

Burger, A. E. 1978. Interspecific breeding attempts by Macronectes giganteus and M. halli. Emu 78: 234–235. [Crossref]

Carboneras, C. 1992. Family Anatidae (Ducks, Geese and Swans). In: del Hoyo J., Elliott A. & Sargatal J. (eds.), Handbook of the Birds of the World. Vol. 1: 536–628. Lynx Edicions, Barcelona.

Carlos, C. J., Voisin, J.-F. & Vooren, C. M. 2005. Records of Southern Giant Petrel Macronectes giganteus solanderi and Northern Giant Petrel M. halli off southern Brazil. Bulletin of the British Ornithologists Club 125: 288–292.

Conroy, J. W. H. 1972. Ecological aspects of the biology of the Giant Petrel Macronectes giganteus (Gmelin) in the Maritime Antarctic. British Antarctic Survey Scientific Report 75: 1–74.

Conroy, J. W. H., Bruce, G. & Furse, J. R. 1975. A guide to the plumage and iris colours of the giant petrels. Ardea 63: 87–92.

Cooper, J., Brooke, M. L., Burger, A., Crawford, R. J. M., Hunter, S. & Williams, T. A. J. 2001. Aspects of the breeding biology of the Northern Giant Petrel (Macronectes halli) and the Southern Giant Petrel (Macronectes giganteus) at sub-Antarctic Marion Island. International Journal of Ornithology 4: 53–68.

Copello, S., Quintana, F. & Somoza, G. 2006. Sex determination and sexual size-dimorphism in Southern Giant Petrels (Macronectes giganteus) from Patagonia, Argentina. Emu 106: 141–146. [Crossref]

González-Solís, J. 2004. Sexual size dimorphism in Northern Giant Petrels: ecological correlates and scaling. Oikos 105: 247–254. [Crossref]

González-Solís, J., Croxall, J. P. & Wood A. G. 2000a. Foraging partitioning between giant petrels Macronectes spp. and its relationship with breeding population changes at Bird Island, South Georgia. Marine Ecology Progress Series 204: 279–288. [Crossref]

González-Solís, J., Croxall, J. P. & Wood, A. G. 2000b. Sexual dimorphism and sexual segregation in foraging strategies of Northern Giant Petrels, Macronectes halliduring incubation. Oikos 90: 390–398.

González-Solís, J., Croxall, J. P. & Afanasyev, V. 2008. Offshore spatial segregation in giant petrels Macronectes spp.: differences between species, sexes and seasons. Aquatic Conservation: Marine and Freshwater Ecosystems 17: S22–S36. [Crossref]

Humphrey, P. S. & Livezey, B. C. 1983. Giant Petrels (Macronectes giganteus) nesting in Chubut, Argentina. Gerfaut 73: 3–8.

Hunter, S. 1982. Interspecific breeding in giant petrels at South Georgia. Emu 82 (suppl.): 312–314. [Crossref]

Hunter, S. 1983. Identification of giant petrels Macronectes spp. Sea Swallow 32: 72–77.

Hunter, S. 1984. Breeding biology and population dynamics of giant petrels Macronectes at South Georgia (Aves: Procellariiformes). Journal of Zoology, London 203: 441–460. [Crossref]

Hunter, S. 1987. Species and sexual isolating mechanisms in sibling species of giant petrels Macronectes. Polar Biology 7: 295–301. [Crossref]

Jiguet, F. 2000. The two giant petrels. Birding World 13: 108–116.

Johnstone, G. W. 1971. Bird in the hand–giant petrels. The Australian Bird Bander 9: 86–87.

Johnstone, G. W. 1974. Field characteristics and behaviour at sea of giant petrels in relation to their oceanic distribution. Emu 74: 209–218. [Crossref]

Johnstone, G. W. 1978. Interbreeding by Macronectes halli and M. giganteus at Macquarie Island. Emu 78: 235. [Crossref]

Johnstone, G. W. Shaughnessy, P. D. & Conroy, J. H. W. 1976. Giant petrels in the South Atlantic: new data from Gough Island. South African Journal of Antarctic Research 6: 19–22.

Mougin, J.-L. 1975. Ecologie comparée des Procellariidae antarctiques et subantarctiques. Comité National Français dês Recherches Antarctiques 36: 1–195.

Obst, B. S. & Nagy, K. A. 1992. Field energy expenditures of the Southern Giant Petrel. Condor 94: 801–810. [Crossref]

Parmelee, D. F. 1992. Antarctic Birds: Ecological and Behavioral Approaches. University of Minnesota Press, Minneapolis.

Patterson, D. L. & Hunter, S. 2000. Giant petrel Macronectes spp. band recovery analysis from the International Giant Petrel Banding Project, 1988/89. Marine Ornithology 28: 69–74.

Patterson, D. L. & Fraser, W. 2000. Foraging movements of Southern Giant Petrels on the Antarctic Peninsula: preliminary findings of a satellite tracking study during the breeding season. In: Flint, E. & Swift, K. (eds.) 2nd International Conference on the Biology and Conservation of Albatrosses and Petrels, Honolulu, Hawaii, USA, 8-12 May 2000. Marine Ornithology 28: 125–152.

Patterson, D. L. & Fraser, W. 2003. Satellite tracking Southern Giant Petrels at Palmer Station, Antarctica. Feature Articles, Microwave Telemetry, Inc. 8: 3–4.

Penhallurick, J. & Wink, M. 2004. Analysis of the taxonomy and nomenclature of the Procellariiformes based on complete nucleotide sequences of the mitochondrial cytochrome b gene. Emu 104: 125–147. [Crossref]

Pennycuick, C. J. 1982. The flight of petrels and albatrosses (Procellariiformes) observed in South Georgia and its vicinity. Philosophical Transactions of the Royal Society of London Series B 300: 75–106. [Crossref]

Quintana, F., Schiavini A. & Copello, S. 2005. Estado poblacional, ecología y conservación del Petrel Gigante del Sur (Macronectes giganteus) en Argentina. Hornero 20: 25–34. [Crossref]

Salomon, M., Voisin, J.-F. & Bried, J. 2003. On the taxonomic status and denomination of the Iberian Chiffchaff. Ibis 145: 87–97. [Crossref]

Shaughnessy, P. D. 1970. The genetics of plumage phase dimorphism of the Southern Giant Petrel Macronectes giganteus. Heredity 25: 501–506. [Crossref]

Shaughnessy, P. D. 1971. Frequency of the white phase of the Southern Giant Petrel, Macronectes giganteus. Australian Journal of Zoology 19: 77–83.

[Crossref]

Shaughnessy, P. D. & Conroy, J. W. D. 1977. Further data on the inheritance of plumage phases of the Southern Giant Petrel Macronectes giganteus. British Antarctic Survey Bulletin 45: 25–28.

Shaughnessy, P. D. & Fairall, N. 1976. Notes on seabirds at Gough Island. South African Journal of Antarctic Research 6: 23–25.


Shirihai, H. & Jarrett, B. 2002. The Complete Guide to Antarctic Wildlife: Birds and Marine Mammals of the Antarctic Continent and the Southern Ocean. Princeton University Press, Princeton and Oxford.

Trivelpiece, S. G. & Trivelpiece, W. Z. 1998. Postfledging dispersal of Southern Giant Petrels Macronectes giganteus banded at Admiralty Bay, King George Island, Antarctica. Marine Ornithology 26: 63–68.

Voisin, J.-F. 1968. Les pétrels géants (Macronectes halli et M. giganteus) de I’lle de la Possession. L’Oiseau et la Revue Française d’Ornithologie (Special No.) 38: 95–122.

Voisin, J.-F. 1976. Observations sur les pétrels géants de l’île aux Cochons (archipel Crozet). Alauda 44: 411–429.

Voisin, J.-F. 1982a. Sur la détermination des pétrels géants Macronectes giganteus et M. halli de l’Océan indien sud. Info Nature, Ile de la Réunion 19: 157–165.

Voisin, J.-F. 1982b. Observations on the Falkland Islands Giant Petrels Macronectes giganteus solanderi. Gerfaut 72: 367–380.

Voisin, J.-F. 1988. Breeding biology of the Northern Giant Petrel Macronectes halli and the Southern Giant Petrel M. giganteus at île de la Possession, îles Crozet, 1966–1980. Cormorant 16: 65–97.

Voisin, J.-F. 1990. Movements of giant petrels Macronectes spp. banded as chicks at Iles Crozet and Kerguelen. Marine Ornithology 18: 27–36.

Voisin, J.-F. & Bester, M. N. 1981. The specific status of giant petrels Macronectes at Gough Island. In: Cooper, J. (ed.) Proceedings of the Symposium on Birds of the Sea and Shore: 215–222. African Seabird Group, Cape Town.

Voisin, J.-F. & Teixeira, D. M. 1998. The identification of giant petrels (Aves, Procellariidae) in the South Atlantic. Boletim da Fundação Brasileira para a Conservação da Natureza 25: 129–134.

Warham, J. 1962. The biology of the Giant Petrel Macronectes giganteus. Auk 79: 139–160. [Crossref]

Woods, R. W. 1975. The Birds of Falkland Islands. Anthony Nelson, Oswestry, England.