Archived 2016 topics: Sharp-beaked Ground-finch (Geospiza difficilis) is being split: list Vampire Ground-finch G. septentrionalis and Genovesa Ground-finch G. acutirostris as Vulnerable?

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for passerines

Lynx Edicions and BirdLife International will soon publish the second volume of the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.

The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.

Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.

The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 2 of the checklist (for passerines) will begin to be incorporated into the 2016 Red List update, with the remainder to be incorporated into subsequent Red List updates.

Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.

Sharp-beaked Ground-finch Geospiza difficilis is being split into G. difficilis, G. septentrionalis and G. acutirostris, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, G. difficilis (BirdLife species factsheet) was listed as Least Concern, on the basis that despite the small range of the species it was considered to have a stable population and had been described as fairly common.

G. difficilis (as defined following the taxonomic change, and incorporating G. d. debilirostris) is found on the islands of Pinta, Fernandina and Santiago in the Galapagos Islands. G. septentrionalis is found on the two tiny islands of Darwin and Wolf in the extreme north west of the Galapagos Islands, and G. acutirostris is found on Genovesa Island only, in the north Galapagos Islands.

The split of this group results in a clear separation of habitat and habit between the newly recognised species. The new nominate Sharp-beaked Ground-finch G. difficilis is a species of structurally complex, dense Zanthoxylum (‘cat’s claw’) forest where they feed on vegetative material, but supply a variety of invertebrates for their nestlings. G. acutirostris occurs in arid scrub, feeding on a similar range of items. However Vampire Ground-finch G. septentrionalis is so named due to sanguinivory. The species opens wounds at the base of the feathers of nesting booby species (Sula spp.) and drinking the blood that ensues. It is posited that this adaptation represents a response to resource scarcity in the late dry season on these arid islands (Scluter and Grant 1984). The species is described as common throughout the two small arid islands on which it occurs (Jaramillo 2016).

The avifauna of the Galapagos Islands face a litany of threats (Wiedenfield and Jiménez-Uzcátegui 2008), perhaps the most severe of which is that from invasive species. The bot-fly Philornis downsi was first discovered in the Galapagos in 1997 and has been demonstrated to reduce fledgling success (Fessl et al. 2006) but at widely varying rates each year (Cimadom et al. 2014), which may be related to rainfall (Dudaniec et al. 2007). P. downsi has been found on 11 out of 13 islands sampled, only being absent in nests examined on the most arid islands of Española and Genovesa (Wiedenfield et al. 2007). Avianpox-like viruses have also been detected in wild populations of other species on the islands with divergent impacts; again there is no assessment of incidence or impacts on the present species (Parker et al. 2011).

Vampire Ground-finch Geospiza septentrionalis is restricted to a maximum area of occurrence (AOO: the actual land area within this range) of barely 2km2, two dots in an extent of occurrence (EOO) of a little over 40km2. The population is believed to be stable and indeed abundant, somewhat dramatically described ‘preying’ on the defenceless chicks in the seabird colonies of the islands ‘lining up behind their victim, patiently waiting their turn to dine’ as reported on the BBC website (Z Gorvett in litt. 2015: http://www.bbc.co.uk/programmes/b04hkysz). However, while the seabirds on which it feeds, for example Red-footed Booby Sula sula (BirdLife Species Factsheet) have a range that wraps around the world, the tiny distribution of G. septentrionalis leaves it potentially at risk of extinction. At present, visiting these islets is strictly controlled and great effort is made to minimise the possibility of the introduction of potentially harmful species. Indeed, recently the eradication of rats from Pinzon demonstrates that hopefully the direction of travel is towards fewer islands with rats (Anon. 2016) has reduced the likelihood of colonisation by this route. However the potential for the introduction of a suitable vector for avian pox is much higher, and the parasitic fly P. downsi, although preferring more humid islands would appear to be a potential risk to the species.

Given the potential threats to a bird with one of the smallest natural ranges of any on the planet, it is suggested that Vampire Ground-finch G. septentrionalis is listed as Vulnerable under criterion D1 + D2.

For the newly split Genovesa Ground-finch G. acutirostris the one island on which it occurs is approximately 15km2 in area, which represents both EOO and AOO for the species. It appears to be abundant, occurring throughout the island and there does not appear to be evidence for any population decline. However, even more so than for Vampire Ground-finch, the tiny range and single island leaves the population at risk from introduced predators or diseases.

It is suggested that G. acutirostris is listed as Vulnerable under criterion D1 + D2.

The EOO for the newly defined Sharp-beaked Ground-finch G. difficilis is approximately 10,000km2, though the maximum AOO is only around 1,150km2. Historically the species also occurred on Isabela, Floreana, San Cristobal and Santa Cruz islands, but has become extinct on all of these prior to 1939, most recently on Santa Cruz (Wiedenfeld 2006). In the remaining range it has been described as uncommon (Jaramillo 2016). No population estimate is available, however it is believed likely that the population exceeds the thresholds for listing as Vulnerable under criterion C as the population is believed to exceed 1,000 mature individuals on at least two of the three islands on which the species occurs, and the overall population is most likely in excess of 10,000 mature individuals. Quantification of the extant population is important. The invasive bot-fly P. downsi is present on both Santiago and Fernandina and while the impact of this at the population level is unclear it should be noted as a potential concern.

Consequently G. difficilis, Sharp-beaked Ground-finch is suggested to be listed as Least Concern.

However, should there be evidence that the population is declining due to invasive species or disease then the number of locations* that the species would be considered to occur at may well be fewer than 10. If so, then the species would warrant listing as Vulnerable under criterion B1ab(v) + B2ab(v).

Comments are invited on these proposed categories and further information would be welcomed.

*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. 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:

Anon. 2016. Post-Rat Eradication and Monitoring on Pinzon. Galapagos Conservancy. Available at: http://www.galapagos.org/conservation/conservation/project-areas/ecosystem-restoration/rat-eradication/. Website accessed 17th October 2016.

Dudaniec, R., Fessl , B. & Kleindorfer, S. 2007. Interannual and interspecific variation in intensity of the parasitic fly, Philornis downsi, in Darwin’s finches. Biological Conservation 139: 325–332.

Fessl, B., Kleindorfer, S., Tebbich, S. 2006. An experimental study on the effects of an introduced parasite in Darwin’s finches. Biological Conservation 127: 55-61.

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

IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN.

Jaramillo, A. 2016. Sharp-beaked Ground-finch (Geospiza difficilis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/62172 on 17 October 2016).

Parker, P.G., Buckles, E.L., Farrington, H., Petren, K., Whiteman, N.K., Ricklefs, R.E., Bollmer, J.L. and Jiménez-Uzcátegui, G. 2011. 110 Years of Avipoxvirus in the Galapagos Islands. PLoS ONE 6: e15989. doi:10.1371/journal.pone.0015989

Schluter, D., and Grant, P. R. 1984. Ecological correlates of morphological evolution in a Darwin’s finch, Geospiza difficilis. Evolution. 38: 856-869.

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. 2010. Quantitative criteria for species delimitation. Ibis 152: 724–746.

Wiedenfeld, D. A. 2006. Aves, The Galapagos Islands, Ecuador. Check List, [S.l.], v. 2, n. 2, p. 1-27. ISSN 1809-127X. Available at: <http://biotaxa.org/cl/article/view/2.2.1>. Date accessed: 18 Oct. 2016. doi:http://dx.doi.org/10.15560/2.2.1.

Wiedenfeld, D.A., Jimenez. U., Gustavo, A., Fessl, B., Kleindorfer, S. & Valarezo, J.C. 2007. Distribution of the introduced parasitic fly Philornis downsi (Diptera, Muscidae) in the Galápagos Islands. Pacific Conservation Biology. 13: 14–19.

Wiedenfeld D,A. and Jiménez-Uzcátegui, G. 2008. Critical problems for bird conservation in the Galápagos Islands. Cotinga 29: 22–27.

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One Response to Archived 2016 topics: Sharp-beaked Ground-finch (Geospiza difficilis) is being split: list Vampire Ground-finch G. septentrionalis and Genovesa Ground-finch G. acutirostris as Vulnerable?

  1. James Westrip (BirdLife) says:

    Based on available information, our preliminary proposal for the 2016 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 of 28 October, 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 2016 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.