Slender-billed Prion Pachyptila belcheri Scientific name definitions

The Slender-billed Prion is a member of the distinctive genus Pachyptila, the prions. Apart from their small size, from afar their general appearance is similar to most procellariids being darker and patterned above and white below. Their most distinctive attribute are broadened mandibles with the upper mandible fringed with lamellae, which is used to filter plankton from the ocean. The Slender-billed Prion feeds using two alternative methods, either ‘surface-seizing’ while pattering over the water or by ‘dipping’ their bills into the water while in flight. The Slender-billed Prion is the most distinctive species of prion due to its very slender bill with which it takes mostly marine crustaceans, though this character is fairly difficult to see well in the field. It occurs in small flocks in the pelagic waters off of South America and in the south Indian Ocean from New Zealand to Africa.

25–28 cm (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); 112–192 g (2 Genevois, F. and Bretagnolle, V. (1995). Sexual dimorphism in voice and morphology in the Thin-billed Prion (Pachyptila belcheri). Notornis. 42(1): 1–10. Close ); wingspan 56 cm. Thin-billed prion  with comparatively little black on tail and sharply contrasting white superciliary . Upperparts  pearl grey to pale grey-blue, slightly darker slate-grey on forehead and crown, contrasting blackish subterminal band on rearmost scapulars and tertials, framed at rear by narrower whitish-grey fringe; upperwing mostly as dorsal plumage but has transversal blackish M on spread wings; uppertail pearl grey to bluish grey, noticeably paler on sides, with black band on central tips; sharply defined and often large white superciliary usually reaching anterior lores, cheeks and lower face, contrasting with slate-grey to blackish mask from just in front of eyes to most of ear-coverts , at rear meeting broad pearl grey to bluish-grey neck-sides, otherwise entirely white underparts  including underwing  and undertail, except broad dark area on central tail, diffuse demarcation between greyish and white on rear body, and thighs largely greyish; iris blackish; bill black on culmen, greyish to cerulean-blue at tip and over rest of bill; legs pale blue to greyish, webs pinkish to flesh. Sexes alike, with only minor dimorphism in size (2 Genevois, F. and Bretagnolle, V. (1995). Sexual dimorphism in voice and morphology in the Thin-billed Prion (Pachyptila belcheri). Notornis. 42(1): 1–10. Close , 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Juvenile similar to adult. Dark M pattern on upperwing often comparatively ill-defined on central wing; perhaps most similar to P. desolata, also has protruding central rectrices, but terminal black tail-band marginally narrower and more restricted to central rectrices, particularly well-defined face pattern with much white in those with mask restricted to narrow line below eye and on upper ear-coverts, broad superciliary usually connects with white cheeks, and bill thinner and slightly shorter.

Southern Ocean, breeding on Noir I (off S Chile) and Falkland Is, and also Crozet Is and Kerguelen Is.

Marine and pelagic , but during breeding often feeds inshore or in shallow offshore waters, sometimes in areas of upwelling. Breeds in coastal areas, with soft or stony soil and low vegetation, or under rocks (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ).

Disperses widely over Southern Ocean after breeding, generally absent from colonies Mar–Sept; birds from Falklands were thought to mainly move W (although some remain in Falklands waters year-round and it is regular visitor to South Georgia in non-breeding season) (3 Prince, P. A., and J. P. Croxall (1996). The birds of South Georgia. Bulletin of the British Ornithologists’ Club 116(2):81–104. Close , 4 Woods, R. W., and A. Woods (1997) Atlas of Breeding Birds of the Falkland Islands. Anthony Nelson, Oswestry, UK. Close ), being recorded in large numbers off W South America, and ranging N to 15° S, where is commonest prion off Chile and Peru (5 Post, P.W. (2007). Observations of prion (Pachyptila) wrecks on the west coast of South America. Notornis. 54(4): 220–225. Close ). However, study in SW Atlantic using geolocators found that this species and P. desolata have divergent migrations and almost complete spatial segregation, with 19 of 20 P. belcheri migrating to an area > 3000 km E of their breeding site, whereas all P. desolata migrated a much shorter distance, and to the NW, and while the range of the former species includes the waters around South Georgia, only when P. desolata is absent (6 Quillfeldt, P., Masello, J.F., Navarro, J. and Phillips, R.A. (2013). Year-round distribution suggests spatial segregation of two small petrel species in the South Atlantic. Journal of Biogeography. 40: 430–441. Close ). Geolocators and analysis of stable isotopes in feathers show that, in contrast, birds from the Kerguelen Is in the Indian Ocean migrate westwards, resulting in an overlapping nonbreeding area in the E Atlantic sector of the Southern Ocean; birds from the Falklands moult at slightly higher latitudes than those from Kerguelen Is.; phenology differs notably between the two populations: Falkland birds return to the Patagonian Shelf after 2–3 months, while Kerguelen birds remain in the nonbreeding area for seven months, before returning to nesting grounds highly synchronously and at high speed (7 Quillfeldt, P., Cherel, Y., Masello, J.F., Delord, K., McGill, R.A.R., Furness, R.W., Moodley, Y. and Weimerskirch, H. (2015). Half a world apart? Overlap in nonbreeding distributions of Atlantic and Indian Ocean Thin-billed Prions. PLOS One. 10(5): e0125007. doi:10.1371/journal.pone.0125007. Close ). Some Indian Ocean birds also move E, occurring regularly off Australia and New Zealand (from where there is a band recovery of a Kerguelen-bred bird) (8 Imber, M.J. (2003). Recovery of Kerguelen-banded thin-billed prion (Pachyptila belcheri) in New Zealand. Notornis. 50(4): 238. Close ). Few records off S Africa, Madagascar and Mauritius (9 Safford, R. J., and A. F. A. Hawkins, Editors (2013). The Birds of Africa. Volume 8. The Malagasy Region. Christopher Helm, London, UK. Close ); generally range N only to 26–30º S (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ), being found in on average colder waters than P. desolata (10 Cherel, Y., Phillips, R.A., Hobson, K.A. and McGill, R. (2006). Stable isotope evidence of diverse species-specific and individual wintering strategies in seabirds. Biol. Lett.. 2: 301–303. Close ). Vagrancy recorded N to Kenya (11 Fanshawe, J. H., P. Prince, and M. Irwin (1992). Black-bellied Storm Petrel Fregetta tropica, Antarctic Prion Pachyptila desolata, and Thin-billed Prion P. belcheri: three species new to Kenya and East Africa. Scopus 15:102–108. Close ), Java (12 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close ) and S Brazil (e.g. Bahia and São Paulo) (13 Olmos, F., Martuscelli, P., Silva, R. and Neves, T.S. (1995). The sea-birds of São Paulo, southeastern Brazil. Bull. Brit. Orn. Club. 115(2): 117–128. Close , 14 Martuscelli, P., Silva e Silva, R. and Olmos, F. (1997). A large prion Pachyptila wreck in south-east Brazil. Cotinga. 8: 55–57. Close ).

Mostly crustaceans (> 95% by mass) (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ), with heavy dependence on amphipods (Themisto gaudichaudii), but also some euphausiids; takes some small squid and fish, while sea skaters (Halobates splendens) have also been recorded in species’ diet, although perhaps taken incidentally (15 Cheng, L., L. B. Spear, and D. G. Ainley (2010). Importance of marine insects (Heteroptera: Gerridae, Halobates spp.) as prey of eastern tropical Pacific seabirds. Marine Ornithology 38(2):91–95. Close ). Copepods apparently absent from diet, unlike other Pachyptila, and this species’ bill lacks lamellae (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). At the Falklands adults prey mostly on squid (Gonatus antarcticus) during incubation but switch to mainly amphipods and euphausids during chick rearing (16 Quillfeldt, P., Michalik, A., Veit-Köhler, G., Strange, I.J. and Masello, J.F. (2010). Inter-annual changes in diet and foraging trip lengths in a small pelagic seabird, the thin-billed prion Pachyptila belcheri. Marine Biology. 157: 2043–2050. Close ); considerable inter-annual differences take place, both in foraging trip lengths and prey switches, in relation to oceanic conditions (17 Quillfeldt, P., Masello, J.F., Brickle, P. and Martin-Creuzburg, D. (2011). Fatty acid signatures of stomach contents reflect inter- and intra-annual changes in diet of a small pelagic seabird, the Thin-billed prion Pachyptila belcheri. Marine Biology. 158: 1805–1813. Close ). Feeds mainly by surface-seizing, dipping and pattering, but also surface-diving, being capable of reaching at least 7·5 m below surface (18 Chastel, O. and Bried, J. (1996). Diving ability of Blue Petrels and Thin-billed Prions. Condor. 98(3): 627–629. Close ). Mainly feeds at night; gregarious when foraging (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ), also associating with P. desolata, but rarely following ships (12 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close ).

Vocal only at night, although activity declines notably on moonlight nights, both because fewer non-breeding individuals visit colonies (which birds are responsible for more calling) and those birds that do visit vocalize less frequently (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Cooing song is sexually dimorphic being strikingly different in timing and syntax (ordering of short and long syllables), given during interaction between pairs (19 Bretagnolle, V., R. Zotier, and P. Jouventin (1990). Comparative population biology of four prions from the Indian Ocean and consequences for their taxonomic status. Auk 107(2):305–316. Close ). Also recorded are a single-note flight call, harsh squawks during antagonostic interactions, a trill during copulation, as well as a rapid succession of single notes (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Chicks use 1–5 begging sessions per night; while the parameters of the first calling session does not reflect body condition, whereas the duration of begging sessions and number of begging calls over the whole night is correlated with body condition and sizes of meals; chicks do not change call frequencies according to state of nutrition and all call parameters, including acoustic parameters of chick begging calls, are highly chick-specific, with strong correlations between call features and chick age (20 Duckworth, A., Masello, J.F., Mundry, R. and Quillfeldt, P. (2009). Functional characterization of begging calls in Thin-billed Prions Pachyptila belcheri chicks. Acta Orn.. 44: 127–137. Close ).

Best studied on Falkland Is (on New I), with additional data from Kerguelen Is (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Starts Oct/Nov, with return to colony commencing in mid Aug (in Falklands) (4 Woods, R. W., and A. Woods (1997) Atlas of Breeding Birds of the Falkland Islands. Anthony Nelson, Oswestry, UK. Close ) and colonies fully occupied by mid Sept, and copulation occurs mid Oct, c. 3 weeks prior to egg-laying (pre-laying exodus), which usually occupies c. 2 weeks; hatching late Dec/early Jan, and fledging mid Feb to early Mar (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close , 21 Quillfeldt, P., Strange, I.J. and Masello, J.F. (2007). Sea surface temperatures and behavioural buffering capacity in thin-billed prions Pachyptila belcheri: breeding success, provisioning and chick begging. Journal of Avian Biology. 38(3): 298–308. Close ). On Kerguelen Is, breeds c. 40 days earlier than sympatric P. vittata (19 Bretagnolle, V., R. Zotier, and P. Jouventin (1990). Comparative population biology of four prions from the Indian Ocean and consequences for their taxonomic status. Auk 107(2):305–316. Close ) and season starts later on Kerguelen than Falklands (2 Genevois, F. and Bretagnolle, V. (1995). Sexual dimorphism in voice and morphology in the Thin-billed Prion (Pachyptila belcheri). Notornis. 42(1): 1–10. Close ). Probably forms long-term pair-bonds (12 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close ), but study on New I using species-specific microsatellites as genetic markers found that seven of 34 chicks (21%) were not fathered by the male (which value is among highest recorded for seabirds) (22 Quillfeldt, P., Masello, J.F. and Segelbacher, G. (2012). Extra-pair paternity in seabirds: a review and case study of Thin-billed Prions Pachyptila belcheri. Journal of Ornithology. 153(2): 367–373. Close ); strongly aggressive towards conspecifics with interspecific competition for nest-sites with Halobaena caerulea (23 Genevois, F. and Buffard, É. (1994). Sites de nidification et caractéristiques des terriers chez deux espèces de petrels sympatriques aux Îles Kerguelen: le Pétrel bleu Halobaena caerulea et le Prion de Belcher Pachyptila belcheri. Alauda. 62(2): 123–134. Close ). Loosely colonial , where is exclusively nocturnal to evade skua (Catharacta) predation (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ), with colony attendance declining on moonlit nights (24 Mougeot, F. and Bretagnolle, V. (2000). Predation risk and moonlight avoidance in nocturnal seabirds. Journal of Avian Biology. 31(3): 376–386. Close ) and behaviour varying according to perceived predation risk by habitat, weather and other parameters (25 Silva, M.C., Granadeiro, J.P., Boersma, P.D. and Strange, I. (2011). Effects of predation risk on the nocturnal activity budgets of thin-billed prions Pachyptila belcheri on New Island, Falkland Islands. Polar Biology. 34: 421–429. Close ); nests in self-excavated burrows (60–350 cm long) (12 Shirihai, H. (2007). A Complete Guide to Antarctic Wildlife. The Birds and Mammals of the Antarctic Continent and the Southern Ocean. Second edition. A. & C. Black, London, UK. Close ), sometimes lined with scraps of available local vegetation (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Single white egg, mean size 48·4 mm × 34·8 mm (Crozets and Kerguelens), mass 28·6–32·7 g (Falklands) (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); incubation 46–47 days, with stints of 4–7 days (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); chicks have grey down and receive a mean 0·4–0·9 meals per night (up to nine days sometimes elapse without meals) (21 Quillfeldt, P., Strange, I.J. and Masello, J.F. (2007). Sea surface temperatures and behavioural buffering capacity in thin-billed prions Pachyptila belcheri: breeding success, provisioning and chick begging. Journal of Avian Biology. 38(3): 298–308. Close ), with adults undertaking mix of short (1–3 days) and long feeding trips (5–9 days) determined by their (not the chick’s) body condition (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); fledging 43–54 (mean 49) days at c. 138–160·5 g, but achieves peak mass of c. 194·5–234 g earlier (21 Quillfeldt, P., Strange, I.J. and Masello, J.F. (2007). Sea surface temperatures and behavioural buffering capacity in thin-billed prions Pachyptila belcheri: breeding success, provisioning and chick begging. Journal of Avian Biology. 38(3): 298–308. Close , 26 Quillfeldt, P., McGill, R.A.R., Furness, R.W., Möstl, E., Ludynia, K. and Masello, J.F. (2012). Impact of miniature geolocation loggers on a small petrel, the thin-billed prion Pachyptila belcheri. Marine Biology. 159: 1809–1816. Close ). Both sexes of prions on New I undertook feeding trips of 1–8 days’ duration (median three days), similar to Kerguelen, while meal sizes increased with longer trips but did not differ between the sexes (27 Quillfeldt, P., Strange, I.J., Segelbacher, G. and Masello, J.F. (2007). Male and female contributions to provisioning rates of thin-billed prions, Pachyptila belcheri, in the South Atlantic. Journal of Ornithology. 148(3): 367–372. Close ). Studies at Kerguelen Is found that hatching success averaged 65% (with desertion main cause of failure), while overall breeding success there estimated at 60%, declining to just c. 30% in poor years (28 Chastel, O., Weimerskirch, H. and Jouventin, P. (1995). Body condition and seabird reproductive performance: a study of three petrel species. Ecology. 76(7): 2240–2246. Close ), whereas on New I in three seasons 2002/03 to 2004/05 laying success was 60–72%, hatching success 57–93%, fledging success 68–90%, with overall breeding success estimated at 23–59%, and starvation, predation (e.g. by Striated Caracaras Phalcoboenus australis and rodents) and nest flooding were the principal causes of losses to be identified (21 Quillfeldt, P., Strange, I.J. and Masello, J.F. (2007). Sea surface temperatures and behavioural buffering capacity in thin-billed prions Pachyptila belcheri: breeding success, provisioning and chick begging. Journal of Avian Biology. 38(3): 298–308. Close ). This study also recorded that sea surface temperatures rose within and between breeding seasons and were negatively correlated with provisioning frequencies by adult prions; chick mass was reduced and begging intensities increased at low feeding frequencies, but overall breeding success and fledging success were not affected, because most chicks survived to fledging despite poor provisioning rates (21 Quillfeldt, P., Strange, I.J. and Masello, J.F. (2007). Sea surface temperatures and behavioural buffering capacity in thin-billed prions Pachyptila belcheri: breeding success, provisioning and chick begging. Journal of Avian Biology. 38(3): 298–308. Close ). Few other data, other than an estimate of annual adult survival of 85% (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ).

Not globally threatened (Least Concern). Total population probably well in excess 2,000,000 pairs and possibly 7,000,000 birds (1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ); up to 1,000,000–2,000,000 pairs have been estimated at Falklands (though just 50,000–100,000 pairs in early 1980s to early 1990s breeding bird survey) (4 Woods, R. W., and A. Woods (1997) Atlas of Breeding Birds of the Falkland Islands. Anthony Nelson, Oswestry, UK. Close ), 700,000–1,000,000 pairs at Kerguelen, with just a few tens of pairs on Crozet Is, has been in burrows on Macquarie I so might breed there (late 1970s) (29 Baker, G. B., R. Gales, S. Hamilton, and V. Wilkinson (2002). Albatrosses and petrels in Australia: a review of their conservation and management. Emu 102(1):71–97. Close ), and large numbers breed on Isla Noir, S Chile, with (at least formerly) perhaps additional colonies elsewhere in region of Tierra del Fuego (e.g. Landfall I) (30 Clark, G. S., A. Cowan, P. Harrison, and W. R. P. Bourne (1992). Notes on the seabirds of the Cape Horn islands. Notornis 39(2):33–144. Close , 1 Brooke, M. (2004). Albatrosses and Petrels Across the World. Oxford University Press, Oxford, UK. Close ). Largest known colony on New I (Falklands) has suffered heavy predation by cats; rats also abundant, as are rabbits in tussock grass habitat where species breeds; recent elimination of some of these introduced predators and revegetation apparently causing increase and expansion, although it also seems to be the case that the prion is naturally resilient at this locality (31 Hilton, G.M. and Cuthbert, R.J. (2010). The catastrophic impact of invasive mammalian predators on birds of the UK Overseas Territories: a review and synthesis. Ibis. 152(3): 443-458. Close ). Est I (Crozet Is) has neither cats nor rats but supports only small colony, presumably due to competition for nest sites with superabundant P. salvini; population at Kerguelen suffers predation by cats. Skuas (Catharacta) dig birds out of burrows , especially in areas of soft peat, but evidence from Kerguelen suggests that bulk of skua predation on this species is of non-breeders attending colonies (24 Mougeot, F. and Bretagnolle, V. (2000). Predation risk and moonlight avoidance in nocturnal seabirds. Journal of Avian Biology. 31(3): 376–386. Close ). More information required on population sizes, trends and main threats; eradication of all alien fauna from breeding islands recommended.