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Acrocephalus aequinoctialis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES PASSERIFORMES SYLVIIDAE

Scientific Name: Acrocephalus aequinoctialis
Species Authority: (Latham, 1790)
Common Name(s):
English Kiritimati Reed-warbler, Bokikokiko
Taxonomic Notes:


   

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(i,iii,v) ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Marks, T., Millett, J., Pierce, R. & Wegmann, A.
Facilitator/Compiler(s): Bird, J., Butchart, S., Derhé, M., Ekstrom, J.
Justification:
This species is listed as Endangered because it is suspected to be confined to just two coral atolls in the Northern Line Islands, Kiribati. It has already been extirpated from one atoll and declines are suspected within the remaining occupied range.

Geographic Range [top]

Range Description: Acrocephalus aequinoctialis is endemic to Kiritimati (Christmas Island) and Teraina (Washington) islands in the Northern Line Islands, Kiribati. It remained common on Teraina in 1980 (Gupta 2007). It formerly occurred on Tabueran (Fanning), but was apparently extirpated in 1972. It was described as 'common' on Kiritimati in 1966 (Pratt et al. 1987), but just 400 individuals were estimated there in 1972 and it was 'scarce in the vicinity of settlement' by 1980 (Sherley 2001). Surveys on Kiritimati in 2007-2011 indicate that the species is widespread and locally common on the mainland and individuals occasionally visit small motu in the lagoons (R. Pierce in litt. 2012). Distribution on Kiritimati is patchy, e.g. there are large areas in the south-east of the island where the warbler is absent due to unsuitable habitat. Densities of up to 50 birds/km2 have been reported on Kiritimati (Pierce et al. 2007).

Countries:
Native:
Kiribati
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population:

Pierce et al. (2007) recorded densities of up to 50 birds/km2 on Kiritimati and pairs reportedly occupy a territory of 1.8-2.3 ha, which coarsely equates to 100 mature individuals/km2. Combined, the islands of Kiritimati and Teraini have a land area of 336 km2, suggesting they could support a maximum of c.16,000-30,000 mature individuals. However, the species is absent from considerable areas of these two islands, likely due to unsuitable habitat, and occurs at lower densities, especially where invasive predators are present. Consequently a global population of 2,500-9,999 mature individuals is suspected, though this may prove to be an overestimate and further surveys are required. This is equivalent to 3,750-14,999 individuals in total, rounded here to 3,500-15,000 individuals.

Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: It occurs in vegetated areas with scattered dominant Tournefortia argentea trees (growing 4-6 m) and Cassytha filiformis mixed with dense Scaevola and many other indigenous shrubs, and sometimes with introduced coconut palms (Cocos nucifera), but not in areas with dense coconuts palms. It is absent from areas that have been cleared or recently burned (R. Pierce in litt. 2012). Birds will cross relatively open grassy areas or sandflats and cross up to 300 m to access motu that have recently been cleared of Rattus exulans (R. Pierce in litt. 2012). The species has also been sighted in gardens close to human habitation (T. Mark in litt. 2010). It feeds on insects, including flies and dragonflies; and small lizards. It spends much of its time foraging on the ground, in low ground cover, and in dead or low branches close to ground level. It is sedentary and a weak flier. Breeding occurs from at least February-July. It is reportedly monogamous; females incubating 2-4 eggs in nests placed just below the canopy of Tournefortia argentea. The territory size is reportedly 1.8-2.3 ha. Maximum densities recorded in 2007 were 0.5 birds/ha (R. Pierce in litt. 2012).

Systems: Terrestrial

Threats [top]

Major Threat(s): The land areas of Kiritimati and Teraina are 322 km2 and 14 km2 respectively, and both support introduced rats Rattus spp.and cats Felis catus (A.Wegmann in litt. 2008), although the spread of black rats R. rattus on Kiritimati appears to have slowed or possibly stopped, with black rats being relatively rare beyond the inhabited areas of the island and outer beaches (R. Pierce in litt. 2012). Although the rate of spread of R. rattus has been unusually slow, it does need monitoring. The successful management of T. argentea trees is likely to be a significant factor for the species (T. Mark in litt. 2010). Hunting by children with slingshots may also pose a threat (A.Wegmann in litt. 2008). Kiritimati Atoll is also suffering from poorly planned immigration leading to widespread degradation of remaining habitats (J. Millet in litt. 2008); principal threats include habitat loss from fires, clearing for coconuts, development and habitat modification (e.g. proliferation of the weed Pluchea indica following fire [Pierce et al. 2007]).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
A survey for the species gathered information on baseline population density, habitat preference and threats in 2007. This survey has made a number of recommendations for further conservation work (Pierce et al. 2007).

Conservation Actions Proposed
Carry out annual monitoring in May-June to determine whether the population is in decline and if so, where and what are the causes, and what contingency plan is best implemented (Pierce et al. 2007, Pierce 2010). Identify suitable habitat that supports the species. Advocate for protection of key habitats from fire, development etc, e.g. by engaging with key landowners, community and Government to identify risks, opportunities, solutions, etc and gaining better community buy-in (Pierce et al. 2007, Pierce 2010). Continue with rodent eradication from Kiritimati motu and monitor outcomes for seabirds and warbler (Pierce and Brown 2009). Use external advice to address biosecurity issues, e.g. spread of Pluchea and the potential arrival of invasive ants (Pierce et al. 2007). All surveyed sites should have the habitat described and rat trapping surveys completed. Implement rat trapping at important sites. Investigate the feasibility of emergency translocations to another island, e.g Orona in Phoenix Islands (Pierce et al. 2007).


Citation: BirdLife International 2012. Acrocephalus aequinoctialis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 24 October 2014.
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