Archived 2016 topics: Red-breasted Chat (Granatellus venustus) is being split: list Granatellus francescae 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.

Red-breasted Chat Granatellus venustus is being split into G. venustus and G. francescae, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, G. venustus (BirdLife species factsheet) was listed as Least Concern as it was not considered to approach any of the criteria for Vulnerable. The habitat of the species was dense scrub, scrubby deciduous woodland, chaparral, semi-arid thorn-forest and second growth with dense understorey (Curson et al. 2016). G. venustus (as newly defined following the taxonomic change) occurs in the west of Mexico from Sinaloa to Chiapas (Curson 2016). It is locally common (Curson 2016), and in the absence of evidence of population declines or imminent threats does not approach the thresholds for listing as Vulnerable under any of the Red List criteria. Hence G. venustus is proposed to be listed as Least Concern.

G. francescae has a limited range, being found on the islands of Madre, Magdalena and Cleofas in the Tres Marias Islands group off the coast of Nayrarit, Mexico (Grant and Cowan 1964). The habitat on the Tres Marias has been threatened by invasive mammals, in particular goats, and a recovery programme is underway to eradicate them (Aguirre-Muñoz et al. 2011). Additional threats include urban development, livestock farming and wood-cutting (Arizmendi and Valdemar 2000).

Tres Marias Hummingbird Cynanthus lawrencei is similarly restricted to the islands, although present on all four islands, and has been assessed as Near Threatened under criteria C2a(i) and D1 +2, on the basis that it occupies a very small range and is estimated to have a small population; however there were not known to be any declines in the population or the species’ habitat.

The total area of the three islands on which G. francescae is present,  is approximately 200 km2, which can be taken as a maximum Area of Occupancy (AOO) for the species. In addition the Extent of Occurrence (EOO) is roughly 500 km2.

The number of locations* inhabited by this species is not straightforward to estimate. As the most significant threat comes from invasive species, it may be reasonable to assume few separate locations, though given the mountainous terrain and lack of evidence of either direct predation or quantification of habitat damage it is considered that the number of locations likely exceeds 10.

The very small AOO likely indicates that the overall population size is similarly small. No density or population estimates exist for the species, and it would be unsound to use density estimates of Granatellus pelzelni from a lowland forest site in Guyana (0.7 inds/km2) to extrapolate to the very different circumstances for this small island species. However, it is unlikely that densities would be sufficiently high (50 inds/km2 over the whole AOO) to exceed 10,000 mature individuals within this area; perhaps it is more likely to be fewer than 2,500 mature individuals, and potentially fewer than 1,000 mature individuals in each subpopulation (assumed to be the three islands on which the species occurs).

As with the Tres Marias Hummingbird, there is no clear evidence of a decline in the population or habitat. It is therefore suggested that the species be listed as Near Threatened under criteria C2a(i); D1+2, on the basis that it occupies a very small range, and is estimated to have a very small population that is potentially at risk from habitat loss, impacts from non-native species and stochasitc events such as hurricanes that could qualify the species as threatened in the near future.

Should evidence be forthcoming that the species is undergoing a decline on the islands, then G. francescae may qualify for listing as Vulnerable under criterion C2a(i).

Comments are invited and further information is most welcome.

*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).

References:

Aguirre-Muñoz, A., Samaniego-Herrera, A., Luna-Mendoza, L., Ortiz-Alcaraz, A., Rodríguez-Malagón, M., Félix-Lizárraga, M., Méndez-Sánchez, F., González-Gómez, R., Torres-García, F., Hernández-Montoya, J. C., Barredo-Barberena, J. M. and Latofski-Robles, M. (2011) Eradications of invasive mammals on islands in Mexico: the roles of history and the collaboration between government agencies, local communities and a non-government organisation. Pp 386-394, in: Veitch, C. R.; Clout, M. N. and Towns, D. R. Island invasives: eradication and management. IUCN, Gland, Switzerland

Arizmendi, Ma. del C. and Valdelamar, L. M. (eds) (2000) Áreas de Importancia para la Conservación de las Aves en México. Mexico City, Mexico: CONABIO.

Curson, J. (2016) Red-breasted Chat (Granatellus venustus). 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/61566 on 25 August 2016).

Grant, P.R., and Cowan, I. McT. 1964. A review of the avifauna of the Tres Marias Islands, Nayarit, Mexico. The Condor 66: 221-228.

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

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.

 

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One Response to Archived 2016 topics: Red-breasted Chat (Granatellus venustus) is being split: list Granatellus francescae as Vulnerable?

  1. James Westrip (BirdLife) says:

    Based on available information, our preliminary proposal for the 2016 Red List would be to list:

    G. venustus as Least Concern.

    G. francescae as Near Threatened under criteria C2a(i);D1+2.

    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 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.