Justification of Red List Category
This species has always had an extremely small range, but volcanic eruptions during the late 1990s caused an extremely rapid population decline and extirpated it from all but two disjunct areas. Deposits of volcanic ash have seriously damaged the habitat of the remaining population, and further deposits or an increased frequency of hurricanes could have devastating effects. However, the population trend has since stabilised or even increased, and the species has therefore been downlisted to Vulnerable. Nevertheless, the total population remains very small and given its extremely restricted range is subject to an obvious plausible future threat (further volcanic eruptions) that could drive the species to become Critically Endangered or even Extinct within a short space of time.
In 2012 the total population was estimated at 307-690 birds (212-1,131, 95% CI), depending on whether the sampling area around each point count was assumed to encompass 100 m or 150 m (Oppel et al. 2014a). The upper estimate comprises 546 (382–897) individuals in the Centre Hills, and 143 (94–234) individuals in the South Soufrière Hills (using a 100 m radius around points); and the lower is based on estimates of 243 (170–399) individuals in the Centre Hills, and 64 (42–104) individuals in the South Soufrière Hills (using a 150 m radius around points; Oppel et al. 2014a). This very roughly equates to 200-460 mature individuals. Previous population estimates were of 460-590 pairs (260-1,190, 95% CI) or 920-1,180 mature individuals, and 5,200 individuals (based on 2004 survey data; Hilton 2008).
A variety of monitoring and analytical techniques indicate annual declines of 8-52% during the period 1997-2000 (Hilton et al. 2003) following a rapid one-off event when a volcanic eruption caused a 60% decrease in range and population in 1996. There was some recovery between 2003 and 2005, and there was no evidence of a continuing population decline between 2000-2013 despite continuing volcanic activity and the presence of native and invasive nest predators, although large uncertainty around trend estimates mean the power to detect a shallow negative trend is very low (Oppel et al. 2014a). Based on the comparison of count data at 42 points, the population in 2013 was 50% of that in 1998 (Oppel et al. 2014a), thus a decline of 30-49% is estimated to have taken place over the past three generations (18 years), but the current population trend is estimated to be stable, as annual monitoring data from 2011-2016 show that the trend is stable or even increasing (S. Oppel in litt. 2016). The probability of extinction after three generations is predicted to be low (2.1% by the year 2028) and future population size is uncertain owing to demographic and environmental stochasticity (Oppel et al. 2014b).
This species inhabits an extremely small area on Montserrat (to UK) in the Lesser Antilles. By the early 1990s, it occurred throughout the three main forested hill ranges on the island (the Centre, Soufrière and South Soufrière hills), but volcanic activity in 1995-1997 entirely destroyed two-thirds of remaining habitat (G. Hilton in litt. 2000, 2003). Initially, only the Centre Hills (c. 14 km2) population was thought to have survived the pyroclastic flows (although even this area was heavily ashed) (P. Atkinson in litt. 1998, 1999, Arendt et al. 1999), but a remnant population was later discovered in a 1-2 km2 forest patch in the South Soufrière Hills, just one km from the summit of the volcano (Bowden et al. 2001). In December 1997, the estimated population was c. 4,000 birds (Arendt et al. 1999), but intensive monitoring between 1997-2003 indicated that the Centre Hills population declined by 40-50%, despite reduced volcanic activity (G. Hilton in litt. 2000, 2003, Hilton et al. 2003). In 2001, 2003 and 2006, further major volcanic eruptions caused heavy ash falls on large areas of the Centre Hills, destroying several nests and curtailing breeding (G. Hilton in litt. 2000, 2003, Anon.2006). The rapid declines noted between 1997-2003 have now ceased and the population has since been stable or even increasing, but population levels remain well below those of 1997 (Oppel et al. 2014a).
It occurs in most forest types between c. 150-900 m, but reaches highest densities in wetter, higher altitude forests, and is absent from areas of very dry forest (Jaramillo and Burke 1999, G. Hilton in litt. 2000, 2003). It is found in all successional stages, and sometimes at the edges of cultivated areas and banana plantations but appears to be an obligate forest species (G. Hilton in litt. 2000, 2003). Nesting occurs in March-August, but the exact timing probably depends on the rainy season (P. Atkinson in litt. 1998, 1999, Jaramillo and Burke 1999). Pre-breeding season rainfall increases food availability which leads to improved body condition of females and increased fecundity (Oppel et al. 2013). Nests are mainly suspended from the leaves of Heliconia caribbaea, although banana and other broad-leaved trees are also used (G. Hilton in litt. 2000, 2003). Its clutch-size is typically two or three. Unsuccessful pairs may attempt up to five clutches; successful pairs can very rarely rear three broods per year (G. Hilton in litt. 2000, 2003). It forages at all levels, but particularly in the understorey, feeding mainly on insects, but occasionally also on fruit and possibly nectar (G. Hilton in litt. 2000, 2003).
Volcanic eruptions in 1995-1997 all but extirpated the species from the Soufrière and South Soufrière hills. Although volcanic activity was reduced in 1998-2000, the population continued to decline (G. Hilton in litt. 2000, 2003, Hilton et al. 2003). Potential causes are low insect availability (Marske et al. 2007) and/or chronic ill-health of birds resulting from ash fall on remaining forest, and other unknown and indirect knock-on effects of volcanic activity (G. Hilton in litt. 2000, 2003). Research into reproductive success, using nest cameras, has also revealed high rates of nest predation by rats and native Pearly-eyed Thrashers Margarops fuscatus, both of which occur at high but fluctuating densities (G. Hilton in litt. 2000, 2003, Bowden et al. 2001). Studies between 1998-2005 found nest success of 29% (n = 275 nests), and 87% of nest failures were due to predation by either introduced rats or Pearly-eyed Thrashers (Allcorn et al. 2012). The availability of non-native fruit trees on Montserrat may have benefited the Pearly-eyed Thrasher population (Oppel et al. 2015). In 2001 and 2003, drought appeared to cause reduced laying frequency and clutch-size, and this may be an increasing problem now that the species is confined to lower, drier areas (G. Hilton in litt. 2000, 2003). Conversely, excessive rainfall can also have a negative impact. A feral pig population is spreading fast and could cause serious damage to the forest habitat if not eradicated, it damages a key nesting plant for Montserrat Oriole, Heliconia caribaea (Oppel et al. 2015). Despite being previously proposed as a threat, there is no nest parasitism by Shiny Cowbird Molothrus bonariensis because this species does not currently occur on Montserrat (P. Atkinson in litt. 1998, 1999), contra Raffaele et al. (1998). Loss of remaining habitat owing to deforestation for agricultural and residential development is also a threat (Oppel et al. 2015). Having a montane distribution that is close to the maximum altitude within its range, this species is also potentially susceptible to climate change (BirdLife International unpublished data).
Conservation and Research Actions Underway
The Centre Hills has been designated a protected area and development is not permitted within its marked boundaries (P. Atkinson in litt. 1998, 1999). A Species Action Plan was published in 2005. There is a comprehensive programme to monitor the population and breeding success (Gibbons et al. 1998, G. Hilton in litt. 2000, 2003). In 2001 a research programme into the causes of the continuing decline was established (Hilton et al. 2002). In June 1999, eight birds were taken by Durrell Wildlife Conservation Trust to Jersey Zoo to enable the development of husbandry techniques; initial attempts at captive breeding proved successful (G. Hilton in litt. 2000, 2003, Owen 2000). As of January 2014 there were 49 captive individuals held in 13 different zoos across the world (Oppel et al. 2015). However there are currently no plans to augment the wild population with birds from captive stock (G. Hilton in litt. 2007, 2008). During 2003, preliminary tests of management interventions were made, aimed at boosting reproductive success (G. Hilton in litt. 2000, 2003). Experimental rat control in the Centre Hills commenced in 2006 with work involving comparing nest success in an area with experimental rat control to adjacent areas with high rat density (G. Hilton in litt. 2007, 2008). However, this project ended in 2008 (L. Bambini in litt. 2017). A project to control feral livestock in the Centre Hills has been running since 2009, funded by the U.K.'s Darwin and Overseas Territories Environment Project initiatives and the EU's BEST initiative (Oppel et al. 2015). Between 2005 and 2008 a project to enable local people to effectively manage the Centre Hills was carried out, associated outcomes included publication of area management plans, as well as detailed socio-economic and biodiversity assessments of the area (Oppel et al. 2015).
Conservation and Research Actions Proposed
Continue the existing programme and research into the causes of the decline. Develop potential management interventions to boost reproductive success (G. Hilton in litt. 2000, 2003). Protect all remaining forests on Montserrat (Allcorn et al. 2012) by addressing forest clearance for development activities, reducing feral livestock populations and introducing effective legislation (Oppel et al. 2015). Continue the close monitoring of the population (G. Hilton in litt. 2000, 2003, Oppel et al. 2014a) and development of breeding programmes. Investigate the reasons for the high densities of nest predators in the Centre Hills (G. Hilton in litt. 2000, 2003), and focus on enhancing nesting success via rat control (Allcorn et al. 2012). Monitor the avifauna on Montserrat to detect arrival of the Shiny Cowbird which could parasitise the nests of Montserrat Oriole (Allcorn et al. 2012).
20-22 cm. Medium-sized, black-and-yellow icterid. Adult male, mostly black with yellowish lower back, rump, shoulder, lower breast, belly and undertail. Female, dull yellowish-green above and yellowish below. Immature duller. Voice Loud whistles and harsh chuur.
Text account compilers
Wege, D., Sharpe, C.J., Stringer, C., Symes, A., Westrip, J., Isherwood, I., Calvert, R., Pople, R., Ashpole, J, Bird, J.
Bambini, L., Atkinson, P., Hilton, G., Oppel, S.
BirdLife International (2020) Species factsheet: Icterus oberi. Downloaded from http://www.birdlife.org on 30/09/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 30/09/2020.