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We document the sighting of four New Zealand Storm Petrels Fregetta maoriana off Gau Island, Fiji, by summarising the circumstances and the identification and ageing of the birds. Like the first record off Gau in May 2017 (Flood & Wilson 2017), these sightings are significant for three reasons. They are only the second confirmed records of New Zealand Storm Petrel away from New Zealand / Australasia. They provide further evidence of long-distance dispersal / migration (Fiji is c.2,000 km north of New Zealand). New Zealand Storm Petrel remains listed as Critically Endangered (IUCN 2022).

We undertook an eight-day pelagic expedition (25 May–1 June 2022) to observe tubenoses off Gau (Ngau), Fiji. The vessel used was the 18-m sailing yacht Sauvage. Wind direction varied between north-east and south-east, and its speed between still and 35 knots, and sea state from flat to 2.5 m: 25–26 May north-east 15–25 knots, 27–29 May east-northeast 10–15 knots (35 knots evening 28 May), 30 May east-southeast 0–5 knots (several hours of heavy rain mid-afternoon), 31 May–1 June east-southeast 10–15 knots. The broader picture saw the dominant trade winds and associated high-pressure system pushed away from Fiji by small low-pressure cells arriving from the south-west.

At given locations, we set up an oil slick using Menhaden fish oil Brevoortia and other fish products. Three locations south of Gau were used: ‘position 1’ c.50 km south (c.25 nm), ‘position 2’ c.30 km south (c.15 nm) and ‘position 3’ c.10 km south (c.5 nm). Most time was spent around position 2. These locations were originally chosen by Shirihai et al. (2009) for their successful at-sea search for Fiji Petrel Pseudobulweria macgillivrayi and were used by Flood & Wilson (2017), yielding the first record of New Zealand Storm Petrel off Gau. Morning and afternoon / evening chumming sessions lasted 3–5 hours. A fish-oil drip at the stern of the yacht was running at all other times in daylight hours.

We recorded four New Zealand Storm Petrels within c.5 km of position 2 (individual birds separated by pattern of streaks on underparts; Fig. 1). On 29 May 2022, three different New Zealand Storm Petrels were observed: bird 1 at 11.19–12.20 h, bird 2 at 15.05–15.24 h, and bird 3 at 16.13 h. On 30 May 2022, one was seen at 16.13–16.22 h.

Identification was based on recently established criteria to separate New Zealand Storm Petrel from New Caledonian Storm Petrel F. lineata (details in Bretagnolle et al. 2022; summarised in Table 1), along with our past at-sea experience of the two. Briefly, New Zealand Storm Petrel is smaller (the size of Wilson's Storm Petrel Oceanites oceanicus), shorter winged, shorter legged, smaller billed, with a different underwing pattern and underparts streaking. All four were seen alongside Wilson's Storm Petrels and were about the same size.

New Zealand Storm Petrel breeds in February–June (egg laying end of February; Rayner et al. 2013; C. Gaskin in litt. 2022). Typically, storm petrels that have bred successfully commence primary moult post-breeding, presumably from July in New Zealand Storm Petrel (depending on post-breeding movements, which are largely unknown). Typically, juveniles from the previous season, non- and failed breeders, commence primary moult a month or so earlier than breeding adults, presumably sometime in May / June for New Zealand Storm Petrel. None of the four was in primary moult, but their primaries were noticeably worn and primary moult might be expected to commence within a month or so. This is consistent with juveniles from the previous year's breeding season, and non- and failed breeders in the current year. It is unlikely that the birds in May off Gau, c.2,000 km north of the breeding grounds, were successful breeders from the 2022 breeding season.

Figure 1.

New Zealand Storm Petrels Fregetta maoriana, c.30 km south of Gau, Fiji, 29 and 30 May 2022, presented in chronological order, top left to bottom right. Note the compact build and relatively small bill. The white underwing panel is broad and clean-looking, with the diagnostic clear-cut border to the longest lesser secondary-coverts and the greater secondary-coverts are unmarked. All four birds show broad dark feathering from the dark lateral undertail-coverts to / beyond the thighs, forming a broad elongated dark band either side of the rear underparts, and streaking is largely confined to the flanks and upper breast. Note the bird top left lacks a toe projection beyond the tail tip because its legs are retracted. Top left and bottom right (Mike Danzenbaker), top right and bottom left (Hiroyuki Tanoi)

TABLE 1

Key differences in structure and plumage that enable field separation of New Zealand Storm Petrel Fregetta maoriana from New Caledonian Storm Petrel F. lineata (based on Bretagnolle et al. 2022). WSP = Wilson's Storm Petrel Oceanites oceanicus.

We considered whether the five birds recorded off Gau (in 2017 and 2022) could represent a previously unrecognised taxon of streaked storm petrel most like New Zealand Storm Petrel, or a northern population of the latter. The possibilities arise because these are the only records of the species away from New Zealand, bar a few off eastern Australia that are pending acceptance by the BirdLife Australia Rarities Committee (T. Palliser in litt. 2022), and thus are geographically isolated from all other records by >2,000 km. However, an unrecognised taxon or northern population of New Zealand Storm Petrel appear improbable based on current knowledge. All historical specimens of streaked storm petrel have been assigned to either New Zealand Storm Petrel or New Caledonian Storm Petrel. Other taxa of Fregetta are known to disperse or migrate long distances. The eastern border of the Australian tectonic plate runs directly north from New Zealand to the region around Fiji and Tonga, forming a significant ridge likely to generate upwelling and food productivity.