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Icterus oberi

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES PASSERIFORMES ICTERIDAE

Scientific Name: Icterus oberi
Species Authority: Lawrence, 1880
Common Name(s):
English Montserrat Oriole

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B1ab(i,ii,iii,iv) ver 3.1
Year Published: 2013
Date Assessed: 2013-11-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S.
Contributor(s): Atkinson, P. & Hilton, G.
Facilitator/Compiler(s): Bird, J., Calvert, R., Isherwood, I., Pople, R., Sharpe, C J, Symes, A. & Wege, D.
Justification:
This species has always had an extremely small range, but recent volcanic eruptions have 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. Although the trend may have since stabilised, the future of this species in the wild remains uncertain, and it consequently qualifies as Critically Endangered. Confirmation of population size and trend may lead to its downlisting in future.

History:
2012 Critically Endangered

Geographic Range [top]

Range Description: 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 1 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 may now have ceased, but population levels remain at less than 50 % of those of 1997, with a total population estimated at just 307-690 birds (212-1,131, 95% CI) in 2012, c.80 % in the Centre Hills and 20 % in the South Soufrière Hills (Oppel et al. 2013).
Countries:
Native:
Montserrat
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: 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. 2013). The upper estimate comprises 546 (382–897) individuals in the Centre Hills, and 143 (94–234) individuals in the South Soufriere 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 Soufriere Hills (using a 150 m radius around points; Oppel et al. 2013). 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).
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: 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). 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).
Systems: Terrestrial

Threats [top]

Major Threat(s): 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). In 2001 and 2003, drought appeared to cause reduced laying frequency and clutch-size, and this may be an increasing problem now that that 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. Despite being previously proposed as a threat, there is no nest parasitism by Shiny Cowbird because this species does not currently occur on Montserrat (P. Atkinson in litt. 1998, 1999), contra Raffaele et al. (1998). 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 Actions [top]

Conservation Actions:

Conservation Actions Underway
There is a comprehensive programme to monitor the population and breeding success (Gibbons et al. 1998, G. Hilton in litt. 2000, 2003), and in 2001 a new research programme into the causes of the continuing decline was begun (Cotinga 17 2002: 7). During 2003, preliminary tests of management interventions were made, aimed at boosting reproductive success (G. Hilton in litt. 2000, 2003). In June 1999, eight birds were taken 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) and captive birds are now also present at several other locations in the UK, but there are currently no plans to augment the wild population with birds from captive stock (G. Hilton in litt. 2007, 2008). 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. Experimental rat control in the Centre Hills commenced in 2006 and work to compare nest success in an area with experimental rat control with nest success in adjacent areas with high rat density was scheduled for 2008 (G. Hilton in litt. 2007, 2008). A pig eradication programme is also planned for the island.

Conservation 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). Continue the close monitoring of the population (G. Hilton in litt. 2000, 2003, Oppel et al. 2013) 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).

Citation: BirdLife International 2013. Icterus oberi. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 24 July 2014.
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