Pterodroma occulta Bonaparte 1856
Creators: name: Flood, Robert L.
name: Wilson, Angus C.
name: Zufelt, Kirk
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Aves
Procellariiformes
Procellariidae
Pterodroma

description: VANUATU PETREL Pterodroma (cervicalis) occulta   
 Observed at sea from c. 50 km south to c. 150 km north of Vanua Lava, Banks Islands, northern Vanuatu, where breeding has recently been documented (Totterman 2009). Birds were sparsely distributed at sea. Nevertheless, our sightings give some indication of foraging range in the breeding season. The rest of our sightings were off Vanua Lava.   
 We arrived at Vanua Lava at noon on 8 January and departed at dusk on 10 January. Late afternoon and evening were spent north-east of Vanua Lava at a ‘hotspot’ for returning Vanuatu Petrels (Shirihai & Bretagnolle 2010; Fig. 4). At night we drifted off north-east Vanua Lava. Morning and midday were mainly spent searching for feeding frenzies of seabirds (frigatebirds Fregata, boobies Sula, noddies Anous and terns Sterna) that often attracted small numbers of Vanuatu Petrels. Groups of 2– 6 P. (c.) occulta were found loafing at sea in the late afternoon and evening, north-east of Vanua Lava, between the Reef Islets and Mota Lava. Birds were observed landing, swimming toward each other, and preening. 8 January—six at sea while approaching Vanua Lava, five in the afternoon with feeding frenzies, then 20 at the ‘hotspot’ in the evening, with two or more calling occasionally 1 km offshore 22.00–23.00 h (the toooooo-wit call described by Totterman 2009: 60). 9 January—six in the afternoon with feeding frenzies, and ten at the ‘hotspot’ in the evening. 10 January— three in the afternoon with feeding frenzies, but none at the ‘hotspot’ before departure at dusk. 11 January—five at sea, mainly with feeding frenzies.   
 Identification of Vanuatu Petrel away from the Banks Islands necessitates correct judgement of size and the extent of white ‘tongues’ on the underside of the primaries beyond the greater primary-coverts (Shirihai & Bretagnolle 2010: 135). We found greater variation in the underwing pattern than Shirihai & Bretagnolle (2010). Their Fig. 6 (p. 137) shows a White-necked Petrel with extensive white ‘tongues’. The legend states that such extensive white has yet to be found in Vanuatu Petrel and might reliably identify White-necked Petrel. On 9 January, we found two same-sized Vanuatu Petrels together on the sea between the Reef Islands and Mota Lava, c. 12 km north-east of Vanua Lava. They eventually flew off. One had a fairly typical underwing pattern, with largely dark primaries, while the other had extensive white ‘tongues’, equivalent to the extreme for White-necked Petrel shown in Shirihai & Bretagnolle (2010: Fig. 6; compare our Fig. 5). At the other extreme, studies in the Kermadec Islands found that 9% of White-necked Petrels had a mainly dark underside to the primaries like typical Vanuatu Petrel (Shirihai & Bretagnolle 2010: 136 and Fig. 8). Consequently, pelagic identification of Vanuatu and White-necked Petrels away from their respective breeding islands will depend solely on correct judgement of size, which of course is difficult to establish at sea.
description: Published as part of Flood, Robert L., Wilson, Angus C. & Zufelt, Kirk, 2017, Observations of five litle-known tubenoses from Melanesia in January 2017, pp. 226-236 in Bulletin of the British Ornithologists' Club 137 (3) on pages 231-232, DOI: 10.25226/bboc.v137i3.2017.a7, http://zenodo.org/record/11558495