Fregetta lineata (Peale, 1848)

Bretagnolle, Vincent, Flood, Robert L., Gaba, Sabrina & Shirihai, Hadoram, 2022, Fregetta lineata (Peale, 1848) is a valid extant species endemic to New Caledonia, Bulletin of the British Ornithologists’ Club 142 (1), pp. 111-130 : 119-123

New Caledonian Storm Petrel Fregetta lineata

Holotype.—The oldest of the three F. lineata specimens ( USNM 15713 ; Fig. 2 ) was collected on Upolu, Samoa, in 1839 by T. R. Peale and described in detail by Mathews (1933). It is the type specimen of Thalassidroma lineata Peale (1848 , Deignan 1961). However, the specimen has not been sequenced, unlike the other two. Probably, the specimen was collected in November 1839, perhaps during 23–25 November, when Peale visited the island. The species was said to be nesting in holes high in the mountains ( Mathews 1933), ‘very high up in the mountains’ ( Murphy & Snyder 1952), possibly the highest point Mt. Fito (c. 1,100 m). Historic records state that a native collected the specimen for Peale, and the latter mentioned these birds were from the mountains. However, the precise circumstances are unclear and it is possible that the storm petrel breeding in the mountains was Polynesian Storm Petrel Nesofregetta fuliginosa ( Bourne 2008) , and that the specimen was collected at sea, as Peale mentioned these birds were commonly observed there. Murphy & Snyder’s (1952) conclusion that the specimen is F. tropica , which is not known to breed in the tropics, led Bourne (2008) to propose that it was collected by Peale in the southern seas and accidentally exchanged with the holotype of Collared Petrel Pterodroma brevipes ( USNM 15459; also collected by Peale). As it is not F. tropica (see above), there is no reason to doubt the locality. USNM 15713 has not been genetically sequenced, its age is unknown, and the skin is damaged.

Measurements.—Wing length 163 mm; tail length 70 mm; culmen (bill length from feathers) 14.5 mm; bill depth (top of maxillary unguis to base of mandibular unguis) 4.8 mm; bill width at base 6.6 mm; tarsus length 37.3 mm.

Second oldest specimen.— AMNH 194110 from the Marquesas ( Fig. 2 ) was described in detail by Murphy (1924) and is a female collected on 15 September 1922 by R. H. Beck, off Ua Pou, Marquesas. It is currently labelled Fregetta guttata ( Mathews 1933, LeCroy 2017) and is the holotype of F. guttata ( LeCroy 2017) . Murphy (1924) initially considered the specimen to be the same taxon as F. lineata ( Peale 1848) , and noted an intermediate structure (foot, nails, rectrices, etc.) between F. grallaria and F. tropica . Mathews (1933) misinterpreted Murphy (1924), confusing F. lineata and F. [g.] titan, and concluded AMNH 194110 represented a new species, even proposing a new genus. However, contra Mathews (1933), Murphy & Snyder (1952) found the differences insufficient to recognise a new taxon and assigned it to F. grallaria , considering ‘ lineata ’ to be a synonym of ‘ grallaria ’ (see also LeCroy 2017). Measurements are given in Appendix 2.

Description.—Consult Figs. 7–9 . Foreparts Head, neck and throat to upper breast blackish brown (old feathers brownish and new ones glossed black). Throat of worn birds may show central pale mottling. Underparts Lower breast, belly to upper ventral region, and flanks contrastingly white with characteristic oval-shaped blackish streaking (feather centres). Streaking somewhat variable in size and shape, but typically each streak broadens at feather tip. Streaks on flanks widest and densest, those on central belly narrowest, and form rows of oval dapples. Dark upper breast border tends to form triangular extensions into sides of white breast. Underwing Striking pattern with following specific characteristics. Broad blackish-brown leading edge, its border contiguous with dark upper breast. Dark leading edge of inner wing involves lesser secondary-coverts, and on outer wing the lesser and central median primary-coverts. Greater primary-coverts mostly greyish black. Median and greater primary-coverts narrowly tipped and edged white. Flight feathers essentially uniform greyish black. Resultant pattern is dark with restricted white underwing panel, which mostly involves median and greater secondary-coverts. However, some greater secondary-coverts can be dark centred, further restricting area of white panel. Upperparts Mantle to back and scapulars essentially blackish brown, shiny greenish / greyish on catching the light. Some mantle and scapular feathers narrowly tipped whitish. Small uppertail-coverts browner, rest white forming a well-defined wide U shape that wraps onto white underside. Upperwing Colour as upperparts, but upperwing-coverts a shade browner, forming an indistinct paler panel. Tail Blackish brown with white basal area on underside mostly concealed by blackish-brown lateral undertail-coverts (with thin white edges) but visible on spread tail. Bare parts Essentially black.

In-hand identification.— F. lineata is distinct from F. grallaria in structure and measurements. Only a few F. grallaria are flecked / streaked on belly ( Fig. 8 ). Murphy & Snyder (1952) stated that such markings are commonly found in F. grallaria . However, they are found on just eight of 68 adults collected near the Juan Fernández Islands ( Chile), and seven of 35 adult F. [g.] titan. Similar statistics occur for F. tropica (AMNH) . Our experience of F. grallaria and F. [g.] titan in the South Pacific, and c. 35 F. tropica specimens from New Zealand, leads to the conclusion that streaking is scarce and irregular, and variable in width and density, unlike the three F. lineata specimens (see Flood 2003, Stephenson et al. 2008b). Variation in intermediate-morph F. g. grallaria from Lord Howe and Kermadec Islands amounts to gradual darkening on the axillaries and flanks, not streaking on the belly, and all but the darkest individuals have a pale belly ( Marchant & Higgins 1990, Stephenson et al. 2008b).

Identification at sea and plumage variation.— F. lineata can reliably be identified at sea with good views and, ideally, in sharp photographs on which it is possible to evaluate details.

Separation from Fregetta storm petrels .—Usually, F. tropica has a thick dark central belly-stripe, sometimes narrow, scarcely broken, and a different structure and behaviour (see below). Usually, F. grallaria has a pure white belly, but a few have irregular thinly distributed flecks / streaks. Scarcely, individuals from all populations of F. grallaria have flanks streaking, narrow and close to feather shafts, never in rows of oval dapples characteristic of F. lineata , or straighter lines characteristic of F. maoriana ( Fig. 8 ). A few extreme examples of F. g. grallaria from Lord Howe display broader flanks streaking, but never across the whole belly ( Fig. 8 ). Also, unlike F. grallaria , F. lineata (and F. maoriana ) have a narrower white ‘rump patch’ on the long uppertail-coverts and a more restricted white underwing panel. Lastly, F. lineata (and F. maoriana ) lack extensive and broad white fringing on fresh upperparts as in most populations of F. tropica and F. grallaria .

Separation from F. maoriana .—Consult Figs. 8‒9 . Similar-looking but individually variable F. lineata is larger, longer winged and longer legged, with different belly streaking and underwing pattern. Belly streaking of F. lineata is typically denser and bolder. White underwing panel of F. lineata typically narrower and less clean-looking (more underwing-coverts have broad dark centres). Border of dark on breast rounder in F. lineata , curving from sides of lower breast to central upper breast, but clearly straighter in F. maoriana . White ‘rump patch’ on long uppertail-coverts averages narrower and rounder in F. lineata . Both species show variation in belly streaking. For example, F. lineata score 4 (16.7% of birds) shows narrower less coalescing streaking, suggesting most heavily streaked F. maoriana score 1 (9.3% of birds). F. lineata score 1 (23.3% of birds) uniquely patterned, with continuous and dense rows of oval dapples, rather than the more straight-lined streaks of F. maoriana (for explanation of scoring see Fig. 9 ). Borderline cases of belly streaking separated when underwing pattern diagnostic. Underwing of F. lineata diagnostic when shows partially dark row of longest lesser secondary-coverts, creating characteristic ragged border to dark leading edge, and has dark centres to greater secondary-coverts. Conversely, a clear-cut border and all-white greater secondary-coverts are diagnostic of F. maoriana (e.g., as evidenced by the first proven record of F. maoriana away from New Zealand, off Fiji; Flood & Wilson 2017). Also consider jizz and behaviour as follows.

Jizz and behaviour.—Once learnt, F. lineata is readily identifiable by jizz, flight and feeding behaviour. Compared to other Fregetta storm petrels , including F. maoriana , note the slimmer build, with proportionately longer and narrower wings, elongated rear body, and long squarer-ended tail. F. lineata has a less square, more angular forehead profile, longer neck, and quite long and thick bill that curves downward. It also has long legs, notably the tibia, which can approach the very long legs of White-faced Storm Petrel Pelagodroma marina , best appreciated when foot-pattering ( Fig. 7 ). Feet relatively ‘huge’, accentuating impression of ‘walking on water’. Unlike other Fregetta that freely ‘ski’ using one foot, this species only occasionally performs short ‘skis’. Rather, it employs both feet simultaneously, occasionally followed by a short ‘ski’. F. maoriana ‘skis’ on one foot in travelling flight, but not habitually like F. tropica and F. grallaria . Travelling flight striking, comprising glides and flaps on stiff wings, close to the sea surface. Collects prey from sea surface like other Fregetta . A bird once dived c. 30 cm to collect small pieces of fish. On several occasions, foraging birds challenged Tahiti Petrel Pseudobulweria rostrata and Gould’s Petrel Pterodroma leucoptera , quickly snatching fish pieces, then escaping. F. lineata may associate with P. leucoptera as they often arrive simultaneously at chum, and F. lineata is always present at large feeding aggregations of P. leucoptera . Also, F. lineata constantly follows feeding Copper Sharks Carcharhinus brachyurus .

Figures

Figure 2. The five historic and one recently discovered museum specimens of New Caledonian Storm Petrel Fregetta lineata and New Zealand Storm Petrel F. maoriana. (A) F. lineata, collected 1839, perhaps 23–25 November, Samoa by T. R. Peale during the US Explorer Expedition, held at National Museum of Natural History, Washington DC (USNM 15713). (B) F. lineata, collected 15 September 1922, presumably at sea, off Ua Pou Island, Marquesas Islands by R. H. Beck during the Whitney South Seas Expedition, held at American Museum of Natural History, New York (AMNH 194110). (C) F. maoriana, collected January–March 1827 by Quoy & Gaimard (1830) during first voyage of the Astrolabe, held at Museum national d’Histoire naturelle, Paris (MNHN C.G. 1829.254 (14393), C.G. 1829 (14372)). (D) F. maoriana, presented by George Carrick Steet of London in February 1895, possibly collected in the Hauraki Gulf, New Zealand (Bourne et al. 2004), held at the Natural History Museum, Tring (NHMUK 1895.2.11.1). (E) F. lineata (left) and Black-bellied Storm Petrel F. tropica (right), beach-cast, Stradbroke Island, Brisbane, Queensland, Australia, held at Queensland Museum, Brisbane (respectively, QM 14391 collected July 1973; and QM 31216, collected 22 May 1999) (Vincent Bretagnolle, except D: Mark Adams, © Natural History Museum, London)

Figure 7. New Caledonian Storm Petrel Fregetta lineata, off Nouméa, New Caledonia, January 2020 (Hadoram Shirihai, © Tubenoses Project)

Figure 8. Comparison of ‘streaked’ White-bellied Storm Petrel Fregetta g. grallaria with New Zealand Storm Petrel F. maoriana and New Caledonian Storm Petrel F. lineata. (A) White-bellied Storm Petrel, Lord Howe Island, Australia, April 2019 (David Newell, www.birdlifephotography.org.au). (B) White-bellied Storm Petrel, Lord Howe Island, February 2017 (Mark Lethlean, www.birdlifephotography.org.au). (C) White-bellied Storm Petrel, Lord Howe Island, date unknown (Jack Shick, www.lhirodenteradicationproject. org/plants-animals/birds). (D) New Zealand Storm Petrel, Hauraki Gulf, North Island, New Zealand, November 2018 (Hadoram Shirihai, © Tubenoses Project). (E) New Caledonian Storm Petrel, off Nouméa, New Caledonia, January 2020 (Hadoram Shirihai, © Tubenoses Project). (F) New Caledonian Storm Petrel, off Nouméa, New Caledonia, January 2020 (Hadoram Shirihai, © Tubenoses Project). Rarely, individuals of all populations of F. grallaria have limited fine streaking, for example (A) and (B), narrow and close to feather shafts, never in rows of oval dapples characteristic of F. lineata, for example (E) and (F), or forming straighter lines characteristic of F. maoriana (D). A few extreme examples of F. g. grallaria from Lord Howe possess broader flanks streaking, e.g. (C), but never covering the whole belly.

Figure 9. Comparison of underparts and underwing patterns of New Caledonian Storm Petrel Fregetta lineata (n = 30), off Nouméa, New Caledonia, January 2020 (top row) and New Zealand Storm Petrel F. maoriana (n = 43), Hauraki Gulf, North Island, New Zealand, November 2018 (bottom row). Variation is scored into four main types for each species, from the heaviest marked (score 1) to lightest marked (score 4). Underparts streaking Both species can show similar coverage of streaking on the white belly and a tendency for denser and / or thicker streaks on the flanks. Score 1 for F. lineata (23.3% of birds) is uniquely patterned, with continuous and dense rows of oval dapples, rather than straighter lines of F. maoriana. Score 2 for F. lineata (36.7%) is the most common and similar to the coverage and shape of streaking as the similarly common score 2 for F. maoriana (34.9%). Streaking on F. lineata tends to be denser and bolder giving the impression it is wider. The unstreaked belly area tends to be cleaner white in F. maoriana. Border of dark breast The border in F. lineata is positioned higher than in F. maoriana, towards the centre of the upper breast, creating a rounder and less straight border than F. maoriana. Underwing pattern In F. lineata, the dark leading edge to the inner wing involves lesser secondary-coverts. The longest of these have partially dark bases creating a characteristic ragged border, with strongly marked bases in 83.3%, limited dark bases in the remaining 16.7%. By contrast, the dark leading edge in F. maoriana invariably shows a clear-cut border on the coverts, only occasionally with a few dark spots in the longest lesser coverts, and never forming a continuous ragged border as in F. lineata. Usually, some greater secondary-coverts and most / all greater primary-coverts in F. lineata have broad dark centres. Thus, the white underwing panel of F. lineata is noticeably less extensive than in F. maoriana (Hadoram Shirihai, © Tubenoses Project)