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Individual study: Translocation of Rarotonga monarchs Pomarea dimidiata to Atiu, southern Cook Islands

Published source details

Robertson H.A., Karika I. & Saul E.K. (2006) Translocation of Rarotonga monarchs Pomarea dimidiata within the southern Cook Islands. Bird Conservation International, 16, 197-215


The Rarotonga monarch (or kakerori) Pomarea dimidiata is a small insectivorous forest passerine, endemic to the island of Rarotonga (21º15' S, 159º45' W) in the southern Cook Islands. By the late 1980s, its population had declined to around 30 individuals, but following intensive control of predators (particularly ship rats Rattus rattus) in its forested hill country habitat, the population recovered to over 200 birds in 2000. Despite this success, the species' small range (c.200 ha) still rendered it vulnerable to a catastrophic event, such as a severe cyclone or the introduction of a novel disease or predator, and so the feasibility of establishing a second 'insurance' population on another, predator-free, island was investigated. This study documents the translocation of 30 young Rarotonga monarchs to Atiu, which was identified as the most suitable island in the southern Cook Islands, owing to the presence of over 1,500 ha of suitable habitat, the apparent absence of ship rats and strong support for the initiative from the Island Council.

Capture and translocation: Candidate birds for translocation were captured in mist-nets at a number of sites within the Takitumu Conservation Area, south-eastern Rarotonga, during August (two months before the breeding season). Captured individuals were given a health check, aged, sexed, colour-ringed, weighed and measured. Ten young birds (yearlings and two-year-olds) were selected each year during 2001-2003, and transported in plywood 'field' boxes (30 × 20 × 20 cm) to the road access, where they were transferred to larger (50 × 30 × 30 cm; full details provided in paper) plywood 'transfer' boxes. Water and food (fruit fly Bactrocera spp. larvae) were provided during the transfer to Atiu.

Releases: Five female and five male monarchs (seven yearlings and three two-year-olds) were released into a patch of forest near Lake Te Roto (20º01' S, 158º07' W) between 19-27 August 2001. Six female and four male yearlings were released in a forested valley 1.5 km east of the 2001 release site between 15-24 August 2002. The final six females and four males (eight yearlings and two two-year-olds) were released between 15-19 August 2003. With the exception of one bird held for 23 hours, all birds were released within 19 hours of capture.

During the 2001–2002 breeding season, a pair (yearling female and two-year-old male) were found 4.5 km north of the release site, but they did not appear to breed. After the breeding season, another pair (both yearlings) was discovered, but no evidence was found to indicate that they had bred. During 2002–2003, both these pairs bred successfully, raising two fledglings each (the maximum family size recorded on Rarotonga), and after the breeding season a further (unidentified) pair was found near the 2002 release site. In spring 2003, 11 ringed birds were located: four from the 2001 translocation, five from 2002 and two from 2003. Five pairs from these ringed birds bred successfully, raising two fledglings each, during the 2003–2004 breeding season. In May/June 2004, a minimum of 15 monarchs were found, including an island-bred yearling.

The removal of 30 young monarchs between 2001 and 2003 had no apparent negative effect on the Rarotonga population, which continued increasing, from 245 in 2001 to 283 in 2003 (after the translocated birds had been removed).

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