Data Zone
Justification of Red List category
The species is currently considered Data Deficient as information on where the species breeds is lacking and hence threats and population trends are largely unknown.
Population justification
Brooke (2004) estimated the global population to exceed 30,000 individuals.
Trend justification
The only known breeding location may be being impacted by rats, but there is no knowledge of the proportion of the population that is found there, and no assessment of the severity of the threat from rats at the site (Carboneras et al. 2018). Therefore, the overall population trend is essentially unknown.
Oceanites gracilis occupies tropical waters of the eastern Pacific Ocean, where it is numerous (Spear and Ainley 2007). The only breeding sites known are for the subspecies gracilis. Prior to 2003, only one nest had ever been found, on Isla Chungungo, Chile (where rats and fire may have caused a decline). During surveys of the island in 2002, three crevices containing perhaps 11 nests were located in the north-east part of the island (Hertel and Torres-Mura 2003). Suitable sites are limited on the island, and alternative sites may be too disturbed by nesting Humboldt Penguins Spheniscus humboldti (Hertel and Torres-Mura 2003). No evidence of rodents or marsupials was found, although the presence of the Short-tailed Snake Tachymenis chilensis may be cause for concern (Hertel and Torres-Mura 2003). Other sites inland in the Atacama Desert (Chile) include a mummified chick found in a crevice at one location (recent DNA analysis has confirmed it to be O. gracilis) and further signs of former activity in many cavities. No live birds have been found despite searches at different times of the year (Schmitt et al. 2015). It is highly likely that O. g. gracilis also breeds in Peru, where it is commonly seen at sea, for example around the islands off Callao, but no breeding site has been found there.
A breeding population (subspecies galapagoensis) is suspected for the Galápagos, Ecuador. Although commonly seen throughout the archipelago and seemingly numerous, re-sightings of banded birds suggest localized populations with indication of limited overlap in spatial use during breeding season. While common, it is possibly not as populous as it might appear from regular observations of flocks at cruise boat anchorages, of birds following vessels, or of birds in open sea between islands where they are observed feeding over dead marine mammals, dumped organic waste, or around fishing vessels (C. Gaskin in litt. 2016). The population on Galápagos appears to be mostly resident; populations from Peru and Chile appear to move further offshore during post-breeding (Spear and Ainley 2007).
It is numerous in the eastern Pacific Ocean and presumably breeds on small rocky islets from Chile north to the Galápagos (Tobias et al. 2006). Birds collected by Beck in May 1913 (also off Callao) had fully enlarged gonads and included a female with an egg ready to lay (Murphy 1936, Brooke 2004), suggesting possible breeding from April to August. Further confirmation of this timing for Peru comes from recent records of grounded O. g. gracilis fledglings for July and August, including an inland site at Lunahuana (C. Gaskin, in litt. 2016). Brood patch data from Galápagos birds captured at sea in 2014 confirmed breeding from May to September; however, despite searches using radio telemetry no breeding site was found (C. Gaskin in litt. 2016).
Rats are thought to be impacting the species at the only known breeding location, but there is no knowledge of the proportion of the population that this location represents, and no assessment of the severity of the threat from rats at the site (Carboneras et al. 2018).
Conservation Actions Underway
None is known.
Text account compilers
Sharpe, C.J., Stuart, A., Symes, A., Hermes, C., Fjagesund, T., Benstead, P., Isherwood, I., Martin, R., McClellan, R., Miller, E., Moreno, R.
Contributors
Ismar , S., Gaskin, C., Hertel, F.
Recommended citation
BirdLife International (2024) Species factsheet: White-vented Storm-petrel Oceanites gracilis. Downloaded from
https://datazone.birdlife.org/species/factsheet/white-vented-storm-petrel-oceanites-gracilis on 25/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 25/12/2024.