Blue Petrel
Halobaena caerulea
Number Of Mature
Individuals (Regional)
210 000 – 291 000
Regional
Population Trend
Decreasing
2025
Regional Category
Vulnerable
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CONTENTSOverview
Names
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IOC English Name: |
Blue Petrel |
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SA & IOC Scientific Name: |
Halobaena caerulea |
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BirdLife International Taxonomy (scientific name): |
Halobaena caerulea |
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Order: |
PROCELLARIIFORMES |
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Family: |
Procellariidae |
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Species name author: |
Gmelin JF 1789 |
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Afrikaans: |
Bloustormvoël |
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Sesotho (South Africa): |
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Sesotho (Lesotho): |
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Siswati: |
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Zulu: |
umantantobunzelimhlophe |
Current Assessment Status
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2025 Regional Category [Criteria] |
VU [A3e] |
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2024 Global Category [Criteria] |
LC (BirdLife International 2020) |
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Population size (Regional) |
210 000 – 291 000 |
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Population size (Global) |
Unknown |
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Distribution size (EOO) (Regional) km2 |
c. 720 (regional; breeding) |
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Distribution size (EOO) (Global) km2 |
96 500 000 (breeding/resident) |
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Distribution size (AOO) (Regional) km2 |
334 (based on colony size); 76 ha (specific area occupied on Marion Island; Dilley et al. 2017a); c. 100 ha on Prince Edward Island; P Ryan, pers obs) |
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Generation time |
c. 9 years (Bird et al. 2020) |
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Status change reason |
Error correction |
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Migrant (in the region) |
Native, breeding visitor |
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Regional endemic |
No |
Historic Listing Information
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2000 Regional Status |
LC |
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2015 Regional Status |
NT [D2] |
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Status change reason (if applicable) |
Application of criteria |
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2015 Population size (Regional) |
c. 300 000 mature individuals |
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2015 Global Status |
LC |
Reason for Inclusion
Reason for Inclusion in the Assessment
Blue Petrel Halobaena caerulea was listed as Near Threatened in the 2015 Regional Red Data Book (Taylor 2015).
Category Justification
Category Justification
The regional population of Blue Petrel breeds at two locations in the region, Prince Edward Island and Marion Island. This species qualifies for Vulnerable (VU) under Criterion A3 due to projected future declines based on expert-assessed extinction horizons due principally to the threat of House Mice Mus musculus on Marion Island (Preston et al. 2019). While there is limited direct evidence of ongoing population decline currently, predictive assessments suggest that the species may experience a significant reduction over the next three generations. The extinction horizon estimates indicate that the species’ population may decline by 40% within this period, exceeding the threshold for VU under A3 (Lee 2025). Although Area of Occupancy (AOO) <500 km2 the other subcriteria for Criterion B2 are not met so Criterion B is not invoked (see Lee 2025 for details).
Since the likelihood of a Regional Rescue Effect is unknown for Blue Petrel, the Category is retained as VU [A3].
Population Justification
Studying burrow-nesting seabirds requires accurate identification of burrow occupants and nest status, which can be difficult, and complicates estimation of population numbers (Bird et al. 2022). Brooke (2004) estimated the global population of the Blue Petrel to number at least 3 000 000 individuals. Ryan and Bester (2008) crudely estimated that 100 000 pairs breed annually on Prince Edward Island and 50 000 pairs on Marion Island. Subsequently, surveys of the breeding population on Marion Island based on burrow counts have estimated the population to be 145 000 breeding pairs in 2012 (95% confidence interval 110 000 to 180 000; Dilley et al. 2017a), and a different approach estimated 124 000 pairs in 2015 (41 000 to 191 000; Dilley et al. 2019). This totals a regional breeding population estimate between 210 000 and 291 000 at the Prince Edward Islands, although previous estimates at Prince Edward Island probably are conservative given the much larger number on Marion Island than initially estimated (Ryan and Bester 2008). Confidence in this regional population estimate is medium. The Prince Edward Islands is thus the third most important breeding locality for Blue Petrels after Diego Ramirez Islands and the Kerguelen Archipelago (Dilley et al. 2017a).
Trend Justification
The global population is thought to be decreasing (BirdLife International 2023). The regional population may be slightly increasing. On Marion Island, breeding success increased shortly after the eradication of Feral Cats Felis catus in 1991 (Cooper et al. 1995) and has been stable since then (Dilley et al. 2018) although estimates have been few. Density of burrows at Marion Island is still much lower than on mouse free Prince Edward Island; the invasive mammal is thought to be behind the slower than expected increase of the population between the late 1970s and the early 2010s (Dilley et al. 2017b). House Mice on Marion Island remain a concern. Future population projections based on extinction horizon estimates suggest that significant reductions may occur within the next three generations (Preston et al. 2019, Lee 2025). While no significant recent declines have been observed, the potential for future declines justifies careful consideration under Criterion A3be (Lee 2025). Ongoing monitoring is essential to validate these projections and determine whether the species is experiencing measurable population decreases.
Biology & Ecology
Taxonomy
Monotypic; Blue Petrel is also the only species in the genus Halobaena. The species is closely related to the prions Pachyptila (Nunn and Stanley 1998, Estandía et al. 2021).
Identification
A small, 26–30 cm petrel with a white forehead, blackish head, and grey upperparts. It has a distinctive white band on the grey tail and a dark “M” pattern on the pale grey wings. Underparts are white, and the bill is slender and dark. Legs and inner toes are pale blue. Both sexes look alike.
Distribution
The Blue Petrel is a circumpolar species that breeds at seven sub-Antarctic Island groups from 40°S to 56°S (Dilley et al. 2017a). While breeding, adults are found in the proximity of the Polar Front (Navarro et al. 2013, Quillfeldt et al. 2020). Outside the breeding season, birds disperse widely throughout the Southern Ocean, but mostly south of the Antarctic Polar Front (Quillfeldt et al. 2017), favouring southern waters to moult (Ryan et al. 2020). The species is a non-breeding vagrant to South African shelf waters, irregularly appearing in large numbers. This behaviour has been observed alongside other Southern Ocean seabird species such as the Kerguelen Petrel Aphrodroma brevirostris (Ryan et al. 1989). Blue Petrels are also occasionally recorded along the South American (Muñoz et al. 2023 and references therein), Australian (Brown et al. 1986), and New Zealand (Powlesland 1986) coasts.
Ecology
Blue Petrels breed in dense, large colonies at the Prince Edward Islands (Fugler et al. 1987). The species shows a distinct preference for burrowing in steep coastal slopes but is found up to 2.5 km inland and to a maximum altitude of 220 m (Dilley et al. 2017a). No demographic data are available for the Prince Edward Islands. A generation length of 8.7 years is estimated by Bird et al. (2020). Blue Petrels are summer breeders with peak laying occurring in the middle of October, hatching in the middle of December and the chicks fledge from the end of January (Fugler et al. 1987). Adults depart the island in February to moult in Antarctic waters (Cherel et al. 2016) and undertake a post-breeding visit to their breeding colony in April/May (Fugler et al. 1987). At Marion Island, the diet of Blue Petrels is dominated by crustaceans followed by fish and cephalopods (Steele and Klages 1986, De Menezes 2023). Sub-Antarctic species dominate the diet but the presence of Antarctic species such as Antarctic krill Euphausia superba is also noted (De Menezes 2023). At the Kerguelen Archipelago, chick-rearing Blue Petrels undertake a dual foraging strategy, alternating short and long foraging trips (Chaurand and Weimerskirch 1994). The stomach content composition observed at Marion Island suggests that chick-rearing adults at Marion Island also use a dual foraging strategy (Steele and Klages 1986, De Menezes 2023).
Threats & Conservation
Threats
The regional population decreased between the early 1950s and late 1980s due to predation by cats on Marion Island (van Aarde 1980). The eradication of cats from the island in 1991 has removed this threat and the species’ breeding success increased from 24% to 64% (Cooper et al. 1995). Blue Petrel was the first species for which predation on chicks and eggs by alien invasive House Mice was suspected (Fugler et al. 1987). Mouse densities have increased on the island, resulting in attacks on other seabirds (Dilley et al. 2018). Nonetheless, predation by mice is thought to be the most likely explanation for the limited recovery of Blue Petrels over the last 30 years (Dilley et al. 2017b). Blue Petrels are also preyed upon by Brown Skuas Catharacta antarctica (Schramm 1983, Cerfonteyn and Ryan 2016), particularly on Prince Edward Island (Ryan et al. 2009). Climate change also poses a threat. Barbraud and Weimerskirch (2003) reported that an exceptionally long-lasting warming from 1994 to 1997 caused a 40% decline of the Blue Petrel population at the Kerguelen Archipelago; suggesting that climate change will strongly impact the species. For all seabirds and particularly densely colonial species such as Blue Petrels, disease outbreaks may threaten the species – although such an outbreak has yet to be recorded for the species at the Prince Edward Islands or elsewhere. Blue Petrels are rarely directly associated with fisheries activities (Melvin et al. 2013), but light pollution on vessels can lead to a high number of fatalities (Black 2005). Finally, plastic pieces were recovered in more than 40% of Blue Petrel samples collected on Marion Island in 2018-2020 (De Menezes 2023), but this presents a clear decrease from the plastic occurrence of over 80% recorded in the middle 1980s (Ryan 1987).
Conservation Measures Underway
No conservation measures focused specifically on the Blue Petrel are currently underway, but various generic conservation principles are in place at its breeding islands. The Prince Edward Islands are listed as a Ramsar Wetland of International Importance, as a Special Nature Reserve under the Environment Conservation Act (No 73 of 1989) and the Prince Edward Islands Management Plan. The Prince Edward Islands Marine Protected Area was proclaimed in 2013. Various stringent guidelines are in place to prevent pollution, contamination, disturbance and introduction of pathogens or invasive organisms on the islands. Further, no access to Prince Edward Island is allowed except for bona fide research purposes at most every four years.
Conservation Measures Proposed
House Mice should be eradicated from Marion Island as soon as possible to benefit Blue Petrels, other seabirds, and the whole island ecosystem. The eradication is being prepared.
Research Priorities and Questions
- Only a crude population estimate is available for Prince Edward Island, and burrow densities in some habitats on the island were estimated in April and September 1979 (Schramm 1986). This should be updated, preferably during the Blue Petrel breeding season to positively identify burrows.
- The last study on the impact of mice on Blue Petrel breeding success dates to 2012 (Dilley et al. 2018); this should be updated in light of the continuation and aggravation of the impact of mice on seabirds at Marion Island.
- Virtually nothing is known about many basic demographic parameters for this species at the Prince Edward Islands. Knowledge of recruitment parameters, longevity, breeding frequency, sex-based differences in parental investment, age/sex structure, etc. would be useful for modelling population trends. Currently, all this information would have to be inferred from the Kerguelen Archipelago, which is located closer to the Polar Front than the Prince Edward Islands; the parameters obtained at the Kerguelen Archipelago may thus not reflect the processes at the Prince Edward Islands.
- Movements of the Blue Petrel during and outside the breeding season are unknown, including the geographical range of juveniles.
Contributors & References
Assessor/s
Maëlle Connan
Reviewer/s
Peter Ryan
References
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Chaurand T, Weimerskirch H. 1994. The regular alternation of short and long foraging trips in the Blue petrel Halobaena caerulea: a previously undescribed strategy of food provisioning in a pelagic seabird. Journal of Animal Ecology 63: 275–282.
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De Menezes L. 2023. Blue Petrels Halobaena caerulea and Salvin’s Prions Pachyptila salvini at Marion Island: updated trophic ecology and plastic loads. MSc, Nelson Mandela University, Gqeberha, South Africa.
Dilley BJ, Davies D, Schramm M, Connan M, Ryan PG. 2017a. The distribution and abundance of Blue Petrels (Halobaena caerulea) breeding at subantarctic Marion Island. Emu 117: 222–232. Available: 10.1080/01584197.2017.1298403.
Dilley BJ, Schramm M, Ryan PG. 2017b. Modest increases in densities of burrow-nesting petrels following the removal of cats (Felis catus) from Marion Island. Polar Biology 40: 625–637. Available: 10.1007/s00300-016-1985-z.
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Dilley BJ, Hedding DW, Henry DAW, Rexer-Huber K, Parker GC, Schoombie S, Osborne A, Ryan PG. 2019. Clustered or dispersed: testing the effect of sampling strategy to census burrow-nesting petrels with varied distributions at sub-Antarctic Marion Island. Antarctic Science 31: 231–242.
Estandía A, Chesser RT, James HF, Levy MA, Obiol JF, Bretagnolle V, González-Solís J, Welch AJ. 2021. Substitution rate variation in a robust Procellariiform seabird phylogeny is not solely explained by body mass, flight efficiency, population size or life history traits. BioRxiv Available: 10.1101/2021.07.27.453752.
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Citation
Connan M 2025. Blue Petrel. In: Lee ATK, Rose S, Banda S, Bezeng SB, Maphalala MI, Maphisa DH, Smit-Robinson H (eds), The 2025 Red Data Book of Birds of South Africa, Lesotho and Eswatini. Johannesburg, South Africa: BirdLife South Africa. Available at: https://www.birdlife.org.za/red-list/blue-petrel/
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