Data Zone
Justification of Red List category
This species qualifies as Critically Endangered as it has a very small range on a single island, and recent information suggests that it is declining rapidly owing to the effects of the dipterid parasite Philornis downsi.
Population justification
The maximum size of the population was estimated at 1,660 individuals in 2008. It is best placed in the band 1,000-2,499 individuals, equating to 667-1,666 mature individuals, rounded here to 600-1,700 mature individuals.
Trend justification
Numbers in 2008 were 39% of those recorded in 2004, indicating a decline outside the range expected for a fluctuating but stable population. Density fell from 154 birds/km2 in 2004 to 60 birds/km2 in 2008 at Cerro Pajas, and it is significantly less common now than it was 50 to 100 years ago (O'Connor et al. 2010a).
Geospiza pauper is endemic to Floreana Island in the Galápagos Islands, Ecuador, where it has a small to moderate population in the highlands, and is uncommon to rare on the coast (Harris 1982, H. Vargas and F. Cruz in litt. 2000, J. O'Connor in litt. 2010). Recent estimates put the total population at not more than 1,660 individuals, and it has recently begun declining rapidly owing to the effects of the introduced dipterid parasite Philornis downsi (O'Connor et al. 2010ab). Its largest population can be found around the base of the volcano Cerro Pajas, where its preferred nesting tree Scalesia pedunculata is dominant (O'Connor et al. 2010a).
It inhabits montane evergreen and tropical deciduous forest, and Scalesia-zone humid scrub (Stotz et al. 1996) mainly at elevations of 300-400 m (O'Connor et al. 2010a). Territory densities amount to 1.7-2.9 territories per ha (Dvorak et al. 2017). It feeds on insects, nectar, young buds and leaves, probing crevices in the bark of trees and searching under twigs and foliage (Castro and Phillips 1996).
The most significant threat is from the introduced ectoparasite Philornis downsi, which occurs in finch nests on Floreana (Wiedenfeld et al. 2007), and is responsible for 41% of nestling mortality (O'Connor et al. 2010a, S. Kleindorfer in litt. 2008). In 2004-2008 nesting success was extremely low in all years (4-8 % of all nests producing fledglings), 28% of nestlings were predated, and parasite intensity from P. downsi was second highest of any bird species studied so far on the Galápagos archipelago (O'Connor et al. 2010a). It is thought to be at elevated risk from fly parasitism because its only extant habitat is adjacent to cleared agricultural land with fruiting trees which are favoured by the adult fly (S. Kleindorfer in litt. 2008). Floreana has a suite of introduced predators and herbivores including cattle, donkeys, pigs, cats, dogs and rats (Jackson 1985), and suffers from extensive habitat destruction and degradation as a result of agriculture (Cruz and Cruz 1996), habitat alteration by invasive plant species, and free-ranging domestic livestock (H. Vargas and F. Cruz in litt. 2000). Avian pox (Avipox virus) occurs on the island and infects a significant proportion of individuals. Predator marks from invasive rodents increased threefold between 2004-2008, and tourist visitation to favoured Scalesia habitat has increased more than tenfold since 2004 (S. Kleindorfer in litt. 2008). Having a montane distribution that is close to the maximum altitude within its range, this species is potentially susceptible to climate change (BirdLife International unpublished data). The species also appears to be at risk from hybridization with Geospiza psittacula and Geospiza parvula, which may have already resulted in the local extinction of G. psittacula on Floreana (Kleindorfer et al. 2014).
Conservation and Research Actions Underway
The Galápagos National Park was gazetted in 1959, and includes almost all the land area of the islands. Although the park incorporates most of Floreana, it does not include the agricultural zone of the island, an area which was the prime habitat for Medium Tree-finch. In 1979, the islands were declared a World Heritage Site (Jackson 1985). In December 2006, the Galápagos National Park began the eradication of goats and donkeys on Floreana which successfully reduced their population to negligible numbers (J. O'Connor in litt. 2010). The Galápagos National Park places rat baiting stations around the Critically Endangered Galápagos Petrel Pterodroma phaeopygia breeding colony in the centre of Cerro Pajas, which may also reduce nest predation of Medium Tree-finches in the immediate area (J. O'Connor in litt. 2010). Methods to control or eradicate Philornis downsi are currently being trialled by researchers and visiting scientists at the Charles Darwin Research Station (J. O'Connor in litt. 2010).
12.5 cm. Chunky finch. Male has black head, greyish-brown upperparts, and whitish or yellowish underparts. Female has greyish-brown head. Similar spp. Differs from Large Tree-finch C. psittacula mainly in substantially smaller and less parrot-like bill, and from Small Tree-finch C. parvulus in larger bill. Voice Five-syllable series of tju notes or a dzi-dzi-dzi.
Text account compilers
Hermes, C., McClellan, R., Isherwood, I., Pople, R., Khwaja, N., Sharpe, C.J., Symes, A., Wright, L
Contributors
Wiedenfeld, D., O'Connor, J., Vargas, H., Kleindorfer, S., Cruz, F.
Recommended citation
BirdLife International (2024) Species factsheet: Medium Tree-finch Geospiza pauper. Downloaded from
https://datazone.birdlife.org/species/factsheet/medium-tree-finch-geospiza-pauper on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/11/2024.