Band-rumped Storm-petrel (Hydrobates castro) is being split: assessment of newly recognised taxa.

Following a taxonomic reassessment, the Band-rumped Storm-petrel, Hydrobates castro, has been split on the HBW/BirdLife International checklist into H. castro and H. jabejabe.

H. castro encompasses the vast majority of the range of the pre-split species and with no evidence to contradict its current listing, it is proposed that this newly recognised taxa be listed as Least Concern. H. jabejabe, on the other hand, has a far more restricted range, only being known to breed in the Cape Verde Islands. Hazevoet (1994) lists the species as breeding on 10 islands, although this has only been confirmed for half of these islands, and Oliveira et al. (2013) provide evidence of possible breeding on Santa Luzia too.

Seabirds in the Cape Verde Islands face a range of threats, of which one of the key ones has been identified to be human exploitation of the breeding colonies (Hazevoet 1994). However, Hazevoet (1994) does stress that this is predominantly directed towards larger species and may not directly affect smaller petrel species. However, for these species a bigger impact may come indirectly because of this threat, with the trampling and collapse of breeding burrows as people try to collect the other, larger species, as well as carrying out other collecting activities (e.g. for shellfish) (Hazevoet 1994). Invasive alien species also impact on seabird colonies, with cats and rats, and potentially mice, posing a predation threat; while goats have had a significant impact on some seabird colonies by trampling breeding burrows (Hazevoet 1994). Pollution and the impact of fisheries were not thought to be having a significant impact in Cape Verde waters in the 1990s (Hazevoet 1994), although the current impact of these potential threats now is not known.

Given its restricted range and this range of threats, therefore, further assessment of H. jabejabe against all criteria appears to be required. This reassessment is given below.

 

Criterion A – Given the threats to seabirds on the Cape Verde Islands, it may be considered that the population size of H. jabejabe is in decline. However, the rate of decline is not known, and so we cannot accurately compare the species to the thresholds for this criterion.

 

Criterion B – The Extent of Occurrence (EOO) and Area of Occupancy (AOO) for this species have not been calculated yet per IUCN guidelines (IUCN 2001, 2012). A rough EOO based solely on a Minimum Convex Polygon around the potential breeding islands would still be greater than the threshold for Vulnerable under criterion B1. However, the AOO of its breeding colonies is likely to be very small and could approach or meet the threshold for Vulnerable (2,000km2). The number of locations* is uncertain, given the uncertainty over which islands the species breeds, but it is likely to be small, and so could approach or meet the threshold for Vulnerable (10 locations). The ongoing threats to seabirds in the Cape Verde Islands also means that we may infer an ongoing population decline and deterioration in the quality of habitat. Therefore, the species likely warrants listing as at least Near Threatened under criterion B2ab(iii,v).

 

Criterion C – Hazevoet (1994) estimated the population size to be at least 1,000 breeding pairs (equivalent to 2,000 mature individuals). The uncertainty over the exact figure means that it may be most appropriate to place the population size in the range 1,000-2,499 mature individuals. Even though breeding takes place at various sites, the ability of seabirds to move large distances, and the proximity of the different islands to one another, suggests that (per IUCN guidelines) the species should be considered to be all in one subpopulation.

Given the potentially ongoing threats acting on the species, particularly those from invasive species, it is tentatively suggested that the species be inferred to be undergoing a continuing decline. Therefore, H. jabejabe would warrant listing as Endangered under criterion C2a(ii).

 

Criterion D – With a population size estimate of 2,000 mature individuals, the population size is too large to warrant listing under criterion D1. The species’s range is also sufficiently large that it would not warrant listing under criterion D2 either.

 

Criterion E – To the best of our knowledge there has been no quantitative analysis of extinction risk carried out for this species. Therefore, it cannot be assessed against this criterion.

 

Therefore, it is proposed that H. castro be listed as Least Concern, while H. jabejabe would warrant listing as Endangered under criterion C2a(ii). We welcome any further information or comments regarding these proposed listings, but please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are about the proposed listing.

 

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

 

References

Hazevoet, C. J. 1994. Status and conservation of seabirds in the Cape Verde Islands. Pp. 279-293 in Seabirds on Islands – Threats, Case Studies and Actions Plans (ed. By D. N. Nettleship, J. Burger and M. Gochfeld). BirdLife Conservation Series, No.1, Cambridge.

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. Available at: www.iucnredlist.org/technical-documents/categories-and-criteria.

Oliveira, N.; Oliveira, J.; Melo, T.; Melo, J.; Geraldes, P. L. 2013. Possible breeding of Cape Verde storm-petrel Oceanodroma jabejabe (Bocage, 1875), on Santa Luzia, Cape Verde Islands. Zoologia Caboverdiana 4(1): 17-20.

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2 Responses to Band-rumped Storm-petrel (Hydrobates castro) is being split: assessment of newly recognised taxa.

  1. Jurek Dyczkowski says:

    About not only Hydrobates/Oceanodroma castro:
    BirdLife uses increasingly more detailed and objective criteria to define species status, but taxonomic decisions what to consider a species versus subspecies are much more subjective.
    I agree that jabejabe deserves separate protection, like many distinctive forms recently elevated to species status. However, BirdLife unwillingly creates a taxonomic chaos because researchers try to elevate subspecies or other forms to a specific status with purpose of getting more conservation attention. So Birdlife unwillingly became a cause contributing to taxonomic inflation and inflation of science publications.
    The most correct approach it probably Birdlife starting to evaluate distinctive subspecies and populations. This would parallel approach in other groups of organisms (fish and big cats, for example). This would lower the pressure on creating as many species as possible.
    Examples of taxa would be several other endemic birds of Cape Verdes (Bourne Heron, Cape Verde Peregrine etc.) which are somehow on the midline between subspecies and species.

  2. Rob Martin (BirdLife International) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2018 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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