Data Zone
Justification of Red List category
This species has an extremely small, severely fragmented range, and only two viable subpopulations. Recent surveys suggest that the number of locations and mature individuals are both declining significantly, and consequently it qualifies as Critically Endangered.
Population justification
The population has not been recorded to number greater than 20 breeding pairs in any year since 2009, falling to a low of just 13 territorial pairs in 2019, of which just 10 bred. The population is therefore estimated to comprise between 20 and 40 mature individuals.
A further 19-23 territorial males without female partners are typically recorded each year in addition to the breeding pairs detailed, a result of rainfall/climatic conditions (Cunninghame et al. 2017, Cunninghame unpubl. data). In 2019, territory and nesting surveys revealed 13 territorial pairs (of which 10 bred), 19 lone territorial males, ~20 additional individuals and 5 newly fledged nestlings, but due to the cryptic nature of juvenile and non-breeding individuals, it is likely that a small percentage of the Mangrove Finch population remains undetected (Cunninghame unpubl. data). The overall population estimate is therefore thought to number 80-100 individuals (F. Cunninghame in litt. 2020).
Trend justification
In 1997 surveys on Isabela found breeding populations in only two areas, Playa Tortuga Negra and Caleta Black on the north-west coast of the island, with estimated populations of 37 and 21 pairs respectively (Grant and Grant 1997, Vargas 1997); but from 2006 to 2009 territory mapping only revealed a maximum of 27 and 15 pairs (Fessl et al. 2010). Further territory mapping from 2010-2019 has recorded further declines with a maximum of 20 breeding pairs recorded in any year since 2009, falling to a low of just 13 territorial pairs in 2019, of which just 10 bred, although up to 19-23 additional territory holding males with no female partner are typically recorded annually (Cunninghame et al. 2017, Cunninghame unpubl. data). This accounts for a further 50-79% decline over a 10 year period. While intensive conservation management is successful at increasing fledging success, overall breeding pair numbers seem to be continuing to rapidly decline and as such, the species is retained as declining,
This species is restricted to the Galápagos Islands, Ecuador. Historically, it was known from at least six mangrove patches on east Fernandina and east, south and west Isabela (Vargas 1997). In 1974, the population was estimated to comprise 100-200 individuals (R. Naveen in litt. 1988). Recent surveys have failed to record the species on Fernandina, and it seems likely that it is now extinct as a breeding bird on the island - the last reported sighting may have been in 1971 (Grant and Grant 1997). No suitable mangrove habitat for breeding finches is thought to remain on Fernandina hence the species is unlikely to breed there again as a result (G. Young in litt. 2020). In 1997 and 1998, surveys on Isabela found breeding populations in only two areas, Playa Tortuga Negra and Caleta Black on the north-west coast of the island, with estimated populations of 37 and 21 pairs respectively (Grant and Grant 1997, Vargas 1997). Subsequent surveys have estimated the population at 36 and 16 pairs in 1999 (Vargas 1999), 24 and 14 pairs in 2007 (B. Fessl in litt. 2007), and thorough surveys recorded c. 40 pairs in 2009 (Fessl et al. 2010). Ongoing thorough annual surveys from 2010-2019 have recorded a decline to fewer than 20 breeding pairs in total (10 pairs bred in 2019) (Cunninghame et al. 2017, Cunninghame unpubl. data). Surveys in the fairly extensive mangroves on the south-east coast of Isabela found three to five territories which probably contained breeding birds, but further areas of potentially suitable habitat remain unsurveyed (Dvorak et al. 1997, Dvorak et al. 2004). In 2008, several other historical sites were surveyed including Punta Espinoza (Fernandina), Bahia Elizabeth, Punta Moreno and Bahia Urbina, but the only site at which birds were located was Cartago Bay (Fessl et al. 2010, G. Young and B. Fessl in litt. 2008), from which the species is now thought extirpated, with no records from the area since 2009 (Young et al. 2013).
It inhabits dense mangrove forests, where it feeds on insects, larvae, spiders and some vegetable matter (Dvorak et al. 1997, Vargas 1997, Dvorak et al. 2004, Fessl et al. 2011). Its breeding season coincides with the beginning of heavy rainfalls, normally in December and January, although in recent years (with a reduction in heavy rainfall events) as late as February, and generally lasts until the end of the rainy season, around May, although successful nesting has been recorded as late as September (Young et al. 2013). Nests are placed as high as 19 m in tall trees within patches of high mangroves that are flood at high tide, a habitat that is rare on the Galápagos (Fessl et al. 2011, Cunninghame et al. 2017). Mangroves used by the species in the north-west appear to be structurally different from areas where it is absent suggesting it has subtle habitat preferences and suffers from habitat degradation (Dvorak et al. 2004, Fessl et al. 2011). It appears to favour mangroves with tall trees, relatively low canopy cover and abundant leaf litter and dead wood (Dvorak et al. 2004, Fessl et al. 2011). A separation of the mangroves from the sea seems to be crucial as this prevents the washing out of leaf litter etc., which represents the species's preferred feeding substrates (Dvorak et al. 2004, Fessl et al. 2011).
This species is declining owing to predation and parasitism as a result of the presence of invasive species.Without control Rattus rattus abundance is high at both breeding sites and was believed to be the major reason for the high nesting failure due to predation (70% in 2007) and low fledgling success (Fessl et al. 2010). Other possible introduced predators include feral cats (especially important during the post-fledging phase), Smooth-billed Ani Crotophaga ani and fire ants Solenopsis spp., although fire ants seemed to have been successfully exterminated in 1997 (Grant and Grant 1997, Vargas 1997, 1999, Cooke et al. 2019). The blood-sucking nest parasite Philornis downsi currently represents the most significant threat, as it is present in all nests and infestation is high (with a mean of 42 parasites per nest) and without management kills close to all chicks (Cunninghame et al. 2015). The first case of nesting mortality due to Philornis parasitisation was recorded in 2007 and has continued to be documented to present (2018), and this threat has become relatively more prominent as invasive rodents are now controlled (Young et al. 2013; Cunninghame et al. 2017). Avian pox will represent a significant threat to the species if this pathogen arrives at the site as mangrove finches have not been exposed to the disease and possess no resilience (F. Cunninghame in litt. 2020). Moreover, due to the low population size, the species is inherently susceptible to the effects of inbreeding (Fessl et al. 2010), loss of genetic diversity and hybridization with the congeneric Woodpecker Finch Geospiza pallida (Lawson et al. 2017). Research has shown that the species favours structurally distinct mangroves, and while the entirety of the habitat is fully protected as part of the Galapagos National Park, it may be especially susceptible to sea level rise driven by climate change (D. Wiedenfeld in litt. 2012).
Observations in 2019 of widespread dieback in over 90% of mature black mangrove (Avicennia germinans) trees at Palaya Tortuga Negra is a further cause for concern (Cunninghame unpubl. data). While Mangrove Finches can survive in the absence of this tree species (there are none at Caleta Black), black mangrove is the species's preferred nest tree and its loss from the forest will further impact on the already vulnerable population; both the cause and the outcome of this situation are unknown and are currently being assessed (Cunninghame unpubl. data). Changes in rainfall are further negatively impacting the population as it results in fewer females attaining breeding condition, and while monitoring shows that adult birds have high year to year survival, females do not respond to males and do not form pairs and breed when dry conditions prevail (Cunninghame unpubl. data). It is presumed that these environmental pressures will only intensify with human induced climate change.
Conservation and Research Actions Underway
The habitat of this species is protected within the Galápagos National Park and, in 1979, the islands were declared a World Heritage Site, although this was classified as threatened in 2007. An action plan was published 2010 (in English and Spanish) following a workshop in 2008. A study of breeding biology commenced in 1999 (Vargas 1999) and a follow up study started in 2006. Since 2006 the Mangrove Finch Project, led by the Charles Darwin Foundation (CDF) and the Galapagos National Park Directorate (GNPD) in collaboration with Durrell Wildlife Conservation Trust (DWCT) has conducted in situ conservation management to reduce the extinction risk to the mangrove finch. Introduced rat control has been successful at reducing nest predation and is continued to date (Fessl et al. 2010, Cunninghame et al. 2017). Possible sites for reintroduction have been visited on Isabela and habitat suitability assessments were undertaken with remote mapping of mangrove habitat throughout Isabela used to locate suitable sites. The first trial translocation took place in May 2010 when nine wild-trapped birds were taken to Bahia Urbina (25 km south of Playa Tortuga Negra) following intense rat control at this site (Cunninghame et al. 2011). While the birds initially established, surveys beyond six months post-release confirmed that none remained and four were observed to have returned to the source site (Cunninghame et al. 2011). Concurrently nest monitoring revealed exceptionally high nestling mortality from P. downsi parasitism with pairs laying multiple clutches to rear at best one or two fledglings late in the season (Cunninghame et al. 2015). Lack of a suitably sized source population to conduct more translocation trials, coupled with the urgency to protect nestlings from P. downsi parasitism, resulted in the Project conducting head-starting (collection of eggs/young nestlings, artificial incubation and captive rearing followed by soft release of juveniles back in their natural habitat). Head starting was conducted in collaboration with San Diego Zoo Global (SDZG) and Auckland Zoo (2017 only) for four consecutive years from 2014-2017 (Cunninghame et al. 2017). Although logistically and technically challenging, this method has proven to be successful, with a total of 39 juveniles having been released. Additionally, observations of several individuals surviving long term and recruitment of <5 individuals to date into the breeding population, highlights the potential of this technique to increase population size. However, technical difficulties, coupled with the invasive nature of head starting for breeding pairs, the difficulty of obtaining accurate data on long term survival of captive reared birds and concurrent research into techniques to protect nestlings in situ (by Philornis Project Collaborators) has resulted in the adoption of intensive in situ mangrove finch nest management to increase nestling survival. Since 2017, during three breeding seasons, mangrove finch nests have been carefully injected with a pyrethrum based liquid (permacap) – this reduces the number of P. downsi larvae in each nest and enables nestlings to fledge successfully in the wild. Additional parasite removal and supplementary feeding of chicks has helped increase the effectiveness of nest injections. While still technically challenging (nest access), this less invasive management technique has ensured a minimum of 26 nestlings to fledge in their natural habitat (Cunninghame, internal report CDF) . Evaluation of conservation techniques is conducted by all project collaborators to ensure that the applied conservation management technique each season is the most effective (Cunninghame et al. 2017). Emerging environmental threats from climate change are predicted to place further pressure on the already fragile mangrove finch population. Planning is already underway with mangrove habitat specialists to enable base line monitoring to better understand the drivers of mangrove habitat die back at the key population sites and determine the potential impacts on the mangrove finch population and the required conservation management. Furthermore, blood samples continue to be collected and DNA analysis of the genetic structure of the remaining population has shown that hybridisation is occurring (Lawson et al. 2017). Additionally results appear to indicate that the species is highly inbred (Fessl et al. 2010, Lawson et al. 2017), however with only a few remaining breeding pairs, no management actions have been identified to remedy this. Additionally, a conservation education programme has engaged local schoolchildren, and produced a film highlighting the species's importance. A course has been run for local guides (G. Young in litt. 2011).
14 cm. Dull, brownish finch. Dull brownish upperparts, more olive on rump. Whitish below with faint streaking. Pale, pointed bill and dark legs. Males can get black hoods with age as do other tree finch species Similar spp. Very similar to Woodpecker Finch Cactospiza pallida, but has smaller bill, some faint streaking on underparts and is slightly browner. Woodpecker finches are not known to get black hoods. Song is best way to differentiate from Woodpecker Finch. Voice Sequence of two-five tur notes, each phrase being repeated up to three times.
Text account compilers
Hermes, C., Everest, J.
Contributors
Benstead, P., Bird, J., Cruz, F., Cunninghame, F., Fessl, B., Harding, M., Isherwood, I., Khwaja, N., McClellan, R., Pople, R., Sharpe, C.J., Symes, A., Vargas, H., Wiedenfeld, D., Wright, L & Young, G.
Recommended citation
BirdLife International (2024) Species factsheet: Mangrove Finch Geospiza heliobates. Downloaded from
https://datazone.birdlife.org/species/factsheet/mangrove-finch-geospiza-heliobates 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.