• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category
This species has a small range, but volcanic eruptions during the late 1990s and early 2000s caused a drastic population decline and extirpated it from all but two disjunct areas. Deposits of volcanic ash have seriously damaged the habitat of the remaining populations, and further deposits or an increased frequency of hurricanes could have devastating effects. The population trend has since stabilised or even increased, and the species has therefore assessed as Vulnerable.

Population justification
In 2012 the total population was estimated at 690 individuals (Oppel et al. 2014a). This estimate comprises 546 individuals in the Centre Hills, and 143 individuals in the South Soufrière Hills. This roughly equates to 460 mature individuals, with 364 mature individuals in the Centre Hills subpopulation and 95 mature individuals in the South Soufrière Hills subpopulation. The population has remained roughly stable since, despite some inter-annual fluctuations (Oppel et al. 2014b, Kitchener 2020).

Trend justification
Prior to 1995, this species was widespread across Montserrat. In that year however, volcanic activity began in the Soufrière Hills: A major eruption in 1996 caused a 60% decrease in range and population, with further eruptions in 2001 and 2003 causing heavy ash falls on large areas of the Centre Hills, destroying nests and curtailing breeding (Arendt et al. 1999; G. Hilton in litt. 2000, 2003; Hilton et al. 2003). In December 1997, the estimated population was c. 4,000 individuals, and intensive monitoring indicated declines by 40-50% in 1997-2003 (Arendt et al. 1999; G. Hilton in litt. 2000, 2003; Hilton et al. 2003).
The rapid declines noted between 1996 and 2003 have now ceased: In 2012 the population was estimated at c. 690 individuals (Oppel et al. 2014a), and monitoring data shows that the population is now overall stable, despite some fluctuations (S. Oppel in litt. 2015, Kitchener 2020). It is however noted that the population levels remain well below those of 1997. Population modelling projects a continuation of the stable trends or small increases up until 2028, though with considerable uncertainty relating to environmental and demographic stochasticity (Oppel et al. 2014b).

This species is endemic to Montserrat (to U.K.) 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 1995-2003 entirely destroyed two-thirds of remaining habitat (G. Hilton in litt. 2000, 2003). Initially, only the population in the Centre Hills 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 small forest patch in the South Soufrière Hills, close to the summit of the volcano (Bowden et al. 2001).

It occurs in most forest types between c. 100-900 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). 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).
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 (Allcorn et al. 2012). 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 (Allcorn et al. 2012).

Volcanic activity during 1995-2003 extirpated the species from the Soufrière Hills, with small populations remaining in the Centre and South Soufrière hills. Although volcanic activity was reduced in 1998-2000, the population continued to decline (Hilton et al. 2003). Potential causes are low insect availability 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; Marske et al. 2007). 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 (Bowden et al. 2001, Allcorn et al. 2012). 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). A feral pig population is spreading and could cause serious damage to the forest habitat if not eradicated, as it damages a key nesting plant for Montserrat Oriole, Heliconia caribaea (Oppel et al. 2015).
Loss of remaining habitat owing to deforestation for agricultural and residential development represents an additional threat (Oppel et al. 2015). Hurricanes however do not impact the population size (Arendt et al. 1999).

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 and revised in 2010 (S. Oppel in litt. 2016). 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).
In June 1999, eight birds were taken by Durrell Wildlife Conservation Trust to Jersey Zoo (U.K.) to enable the development of husbandry techniques; initial attempts at captive breeding proved successful (G. Hilton in litt. 2000, 2003; Owen 2000). As of 2020 there were 56 captive individuals held in several zoos across Europe (Kitchener 2020). However, there are currently no plans to augment the wild population with birds from captive stock (G. Hilton in litt. 2007, 2008).

Conservation and Research Actions Proposed
Develop potential management interventions to boost reproductive success. Continue detailed surveys to regularly monitor the population size.
Protect remaining forests on Montserrat. Continue the development of captive breeding programmes and investigate the potential for reintroductions. Continue and expand the control and eradication of nest predators. Reduce feral livestock populations.

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
Hermes, C.

Contributors
Ashpole, J, Atkinson, P., Bambini, L., Bird, J., Calvert, R., Hilton, G., Isherwood, I., Oppel, S., Pople, R., Sharpe, C.J., Stringer, C., Symes, A., Wege, D. & Westrip, J.R.S.

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Recommended citation
BirdLife International (2024) Species factsheet: Montserrat Oriole Icterus oberi. Downloaded from https://datazone.birdlife.org/species/factsheet/montserrat-oriole-icterus-oberi on 24/12/2024.
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 24/12/2024.