Wilson’s Storm-Petrel: Does the Most Abundant Seabird Still Exist?
Introduction The Wilson’s Storm-Petrel (Oceanites oceanicus) is considered the world’s most abundant seabird. With a population estimated at 8-20 million individuals (BirdLife International 2024), its breeding range spans the Southern Ocean, from Antarctica to subantarctic islands. During the austral winter, it migrates across the equator into the North Atlantic, Pacific, and Indian Oceans (Brooke 2004). Despite its abundance, unresolved questions about its taxonomy and range persist, particularly in Australian waters.
Taxonomy and Phylogeny Wilson’s Storm-Petrel is a polytypic species, currently classified into three subspecies: O. o. oceanicus, O. o. exasperatus, and O. o. chilensis (Clements et al., 2023). Its closest relatives include Elliot’s Storm-Petrel (O. gracilis; O. g. gracilis and O. g. galapagoensis) and the monotypic Pincoya Storm-Petrel (O. pincoyae) (Harrison et al., 2013). Recent studies have suggested splitting the Fuegian Storm-Petrel (O. chilensis) and Lowe’s Storm-Petrel (O. galapagoensis) into separate species (Howell & Zufelt 2019), elevating the Antarctic Storm-Petrel (O. exasperatus) to species status and recognising the Andean Storm-Petrel (O. barrosi) as a new species (Norambuena et al., 2024). This would expand the genus Oceanites from three to seven species:
- Oceanites chilensis (Fuegian Storm-Petrel)
- Oceanites exasperatus (Antarctic Storm-Petrel)
- Oceanites gracilis (Graceful Storm-Petrel)
- Oceanites pincoyae (Pincoya Storm-Petrel)
- Oceanites barrosi (Andean Storm-Petrel)
- Oceanites galapagoensis (Lava Storm-Petrel)
- Oceanites oceanicus (Subantarctic Storm-Petrel)
Phylogenetic analysis has uncovered surprising relationships that do not align with phenotypic features. For instance, the Pincoya Storm-Petrel is closely related to the Andean Storm-Petrel, while the Lava Storm-Petrel groups with the Subantarctic Storm-Petrel, rather than the Graceful Storm-Petrel. The Antarctic Storm-Petrel appears to be a sister group to the other species, with the Fuegian Storm-Petrel being the most basal.
Wilson’s Storm-Petrel in Queensland: The Possibility of Other Taxa In Queensland, Wilson’s Storm-Petrel is the most common storm-petrel in pelagic waters, but other Oceanites taxa may also occur. Species like the Graceful, Pincoya, and Lava Storm-Petrels are easily distinguished by their distinct white belly plumage (Norambuena et al., 2024). However, no such birds have been reported in Australian waters (BirdLife Australia Rarities Committee Reports Archive 2024). Similarly, the Andean Storm-Petrel, with its limited but conspicuous white belly tips, is an unlikely candidate for Queensland waters. The Fuegian Storm-Petrel closely resembles ‘classic’ Wilson’s Storm-Petrel and could potentially be misidentified, but given its ecology and distribution, it is unlikely to be a regular visitor. This leaves two main possibilities: the Antarctic Storm-Petrel and the Subantarctic Storm-Petrel. Norambuena et al. (2024) suggest only the Antarctic Storm-Petrel migrates into the northern hemisphere, but but not the Subantarctic Storm-Petrel. The Antarctic Storm-Petrel breeds in regions like the South Shetland Islands and migrates across the equator, while the Subantarctic Storm-Petrel breeds on islands like Crozet, Heard, and Macquarie Island.
The Antarctic Storm-Petrel is generally noted for longer wings and tails (but with substantial overlap), possibly an adaptation for long-distance migration. Observations of Wilson’s Storm-Petrels in Southeast Queensland have revealed size differences, raising the possibility that either the Antarctic (likely) or Subantarctic Storm-Petrel, or both, might be present in Australian waters. Further research, including genetic analysis and field measurements, is needed to determine whether these size differences are due to natural variation or indicate the presence of distinct taxa.
Conclusion The potential presence of Antarctic and Subantarctic Storm-Petrels in Queensland waters warrants further investigation, as it could provide valuable insights into the migratory and ecological patterns of these enigmatic seabirds. With advances in genetic analysis and continued field observations, future studies may resolve these uncertainties and lead to a clearer understanding of the Wilson’s Storm-Petrel complex in Australia.
References
- BirdLife Australia Rarities Committee Reports Archive (2024)
- BirdLife International (2024) Species factsheet: Wilson’s Storm-petrel Oceanites oceanicus
- Brooke M (2004). Albatrosses and Petrels Across the World. Oxford University Press
- Clements JF et al. (2023) The eBird/Clements Checklist of Birds of the World
- Harrison, P., et al. (2013) A new storm-petrel species from Chile. Auk, 130(1), 180–191
- Howell SNG & Zufelt K (2019). Oceanic Birds of the World. Princeton University Press
- Norambuena HV et al. (2024) Resolving the conflictive phylogenetic relationships of Oceanites. Zootaxa 5486 (4): 451–475
