This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2015.
Large Tree-finch Camarhynchus psittacula is restricted to the Galápagos islands, Ecuador, with breeding populations on Isabela, Santa Cruz, Santa Fé, Fernandina, Santiago, Floreana, Marchena, Pinta and Rábida (Castro and Phillips 1996, Stotz et al. 1996). It is extinct on Pinzón (Castro and Phillips 1996). It is currently listed as Least Concern because it was not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria. Although this species may have a small range (estimated at 7,100 km2), it was not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend was thought to be stable, and hence the species did not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, and although it was described as ‘uncommon’ in at least parts of its range (Stotz et al. 1996), it was not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure).
A recent study by Dvorak et al. (2012) used quantitative census data to describe the distribution and abundance of the land birds of Santa Cruz; the second largest island in the Galapagos archipelago. The Large Tree-finch declined significantly in the dry zone between 1997 and 2010, although this zone was not the species’s stronghold. No declines were recorded in the Scalesia zone, which still holds the highest densities of this finch, despite the fact that little remains of this once expansive forest (Dvorak et al. 2012). The population size of this species was estimated at 9,000 singing males, largely confined to higher altitudes. No census data currently exists for bird species on the other two elevated islands of Isabela and Santiago, but given the level of habitat destruction and degradation by introduced herbivores on those islands (Henderson & Dawson 2009), similar impacts on this species’s population are suspected there (Dvorak et al. 2012).
The EOO of this species is estimated to be <20,000 km2; if it is known to exist at no more than 10 locations (based on the assumption that it is reasonable to consider each island as a separate location, consistent with the treatment of other Galapagos endemics), and it is inferred to be undergoing continuing declines in the Area, extent and/or quality of habitat and number of mature individuals, it would warrant uplisting to Vulnerable under criteria B1ab(iii,v) of the IUCN Red List. If there is evidence to suggest that the global population of this species has reduced by >30% over the past 11 years (three generations), with an inferred decline based on index of abundance, and declines at a similar rate are projected to continue within the next 11 years, this species would warrant uplisting to Vulnerable under criteria A2b+3b+4b.
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). For example, where the most serious plausible threat is habitat loss, a location is an area where a single development project can eliminate or severely reduce the population. Where the most serious plausible threat is volcanic eruption, hurricane, tsunami, frequent flood or fire, locations may be defined by the previous or predicted extent of lava flows, storm paths, inundation, fire paths, etc.
Further information is requested on this species’s global population trends, size and distribution. Comments on the severity of threats to this species are also welcome.
Dvorak, M, Fessl, B, Nemeth, E, Kleindorfer, S. and Tebbich, S. (2012) Distribution and abundance of Darwin’s finches and other land birds on Santa Cruz Island, Galapagos: evidence for declining populations. Oryx 46(1), 78-86.
Henderson, S. and Dawson, T. P. (2009) Alien invasions from space observations: detecting feral goat impacts on Isla Isabela, Galapagos Islands with the AVHRR. International Journal of Remote Sensing 30, 423–433.
Stotz, D. F., Fitzpatrick, J. W., Parker III, T. A. and Moskovits. D. K. (1996) Neotropical birds: ecology and conservation. Chicago, IL: University of Chicago Press.