|Scientific Name:||Pomarea dimidiata|
|Species Authority:||(Hartlaub & Finsch, 1871)|
|Red List Category & Criteria:||Vulnerable D1+2 ver 3.1|
|Reviewer/s:||Butchart, S. & Symes, A.|
|Contributor/s:||Ghestemme, T., O'Brien, M., Robertson, H. & Saul, E.|
Once among the rarest birds of the world, this species has been brought back from the brink of extinction. It has been downlisted to Vulnerable as the population has increased in recent years owing to intensive conservation efforts with no evidence of a continuing decline for for the last five years. However, it still has a very small population and range and remains threatened by chance events such as cyclones other stochastic factors that could drive it to qualify as Critically Endangered or even Extinct in a short time period. The survival of the species remains dependent on a continuation of intensive conservation efforts.
Pomarea dimidiata is endemic to Rarotonga, Cook Islands, where it is largely restricted to the Totokoitu, Turoa and western Avana Valleys. It was common until the middle of the 19th century, but thought to be extinct in the early 1900s (Robertson et al. 1994). A survey in 1983 located only 20 birds and two nests, and estimated a population of 35-50 birds (Hay 1986, H. Robertson in litt. 2005). A recovery plan initiated in 1987 has improved breeding success and recruitment, and decreased mortality of adults, resulting in 177 birds in 1998, 196 in 1999, 222 in 2000, 255 in 2001, 289 in 2002 and 308 in 2003 (H. Robertson in litt. 2007). In 2001, ten birds were translocated from Rarotonga and released on Atiu, 200 km north-east; similar numbers, consisting of one to two-year-old birds, were translocated to Atiu in 2002 and in 2003 (Robertson et al 2006). Four fledglings were recorded on Atiu in autumn 2003 (World Birdwatch 2003). By August 2004, at least 281 birds were found on Rarotonga, and 25 on Atiu, giving an overall estimated population of 306 individuals. However, five cyclones passed through the southern Cook Islands in five weeks in summer 2005 and though direct mortality was less than expected, a very poor breeding season followed, with the population estimated at 291 individuals in August 2006; 255 on Rarotonga and 36 on Atiu (Robertson and Saul 2007). By 2007, the population had increased to 314 birds; 271 on Rarotonga and 43 on Atiu (Robertson et al. 2009) and by August 2011 (supplemented by data from July 2011), the population was estimated at c.380 birds, including 69 yearlings (Robertson et al. 2011, H. Robertson in litt. 2011), suggesting a population of c.310 mature individuals.
|Range Map:||Click here to open the map viewer and explore range.|
The population was estimated at 296-300 in August 2004, but a subsequent series of devastating cyclones in early 2005 lead to a decline, especially on Rarotonga. The total population began to increase in 2007 due to good recruitment on Atiu (where 30 birds were transferred in 2001-2003) and a stable population on Rarotonga. In 2011 the population was estimated at c.380 birds, including 69 yearlings (Robertson et al. 2011, H. Robertson in litt. 2011), suggesting a population of c.310 mature individuals.
|Habitat and Ecology:||
It prefers steep-sided, wet, forested, small valleys sheltered from south-east trade winds in the headwaters of streams. It feeds mainly on small caterpillars, flies, beetles and bugs. Clutch-size is two. Usually only one brood is raised each year (McCormack and Künzle 1990, Sanders et al. 1995, Saul et al. 1998, E. Saul in litt. 1999). Before intensive predator control began, annual adult mortality was 24.3% and life expectancy was 3.6-6.0 years for males and 2.4 years for females. Since intensive management, annual mortality has dropped significantly to 14.2% and life expectancy has increased to 7.6 years for males and 6.3 years for females (H. Robertson in litt. 2007). The species is reportedly capable of breeding at one year old, but more recently, it is rare for yearlings to breed (<5%), and most do not start breeding until 3-4 years old (H. Robertson in litt. 2012).
|Major Threat(s):||The species's highly localised distribution leaves it vulnerable to cyclones, invasion of weeds and forest clearance. It continues to be threatened by black rat Rattus rattus and cats Felis catus. Predation by Long-tailed Cuckoo Eudynamys taitensis, a winter migrant from New Zealand, remains a possibility. The introduction of avian diseases could have a major impact, as could invasion by new predators (e.g. snakes and mongooses) (Robertson et al. 1994, H. Robertson verbally 1999, E. Saul in litt. 1999). Despite passing through a bottleneck of 29 birds, the genetic diversity in the species is moderately good and in line with the population being near that bottleneck size for only a short period of time and so inbreeding effects and loss of genetic diversity are not thought to be a threat (H. Robertson in litt. 2012).|
Conservation Actions Underway
The valleys where the species survives (called the Takitumu Conservation Area) are managed by three landowning families who are developing an ecologically and commercially sustainable ecotourism venture. Intensive rat control is carried out during the breeding season, including fortnightly poisoning (H. Robertson verbally 1999, Robertson 2000). An insurance population has been established on Atiu and is breeding well in a variety of habitats (Robertson et al 2006, Saul et al 2007). The species's survival remains dependent on the continuation of such intensive conservation action.
Conservation Actions Proposed
Continue monitoring the population. Continue rat control in designated areas. Maintain the existing management programme. Maintain and (wherever possible) increase the training of local Cook Islanders in implementing the management programme. Win community support for occasional further translocations to Atiu to maintain genetic diversity in that population (Robertson et al. 1994, SPREP 1999). Ensure new predators do not become established on Rarotonga. Monitor to ensure no predators become established on Atiu.
|Citation:||BirdLife International 2012. Pomarea dimidiata. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 20 May 2013.|
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