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Rarotonga monarch
The Rarotonga monarch (''Pomarea dimidiata''), , also known as the Rarotonga flycatcher,〔(【引用サイトリンク】title= Rarotonga Flycatcher )〕 is a species of bird in the monarch flycatcher family Monarchidae. It is endemic to the Cook Islands.
It is a most unusual bird in a number of ways, being the only bird known to undergo sequential changes in plumage as it grows 〔(“Conservation of kakerori (''Pomarea dimidiata'') in the Cook Islands in 2004-05” )〕 from orange to orange-grey to pure grey when maturity is reached after four years. Owing to its tropical oceanic island location, the kakerori is exceptionally long-lived for a bird with a mass of ,〔 having an adult survival of between 85 and 89 percent, a life expectancy of seven to nine years, and a maximum lifespan from a single banding scheme started in the middle 1980s of around 24 years. These figures are comparable to large Australian passerines like the superb lyrebird or satin bowerbird〔See (Australian Bird and Bat Banding Scheme )〕 and more than ten times the life expectancies of similar sized Holarctic songbirds. Such extraordinary longevity may explain the evolution of helpers at the nest in a family where this feature is otherwise completely absent:〔(Distribution of known and inferred modes of parental care in families and subfamilies of birds )〕 males can breed at one year, but do not do so in practice until they are four.〔(“Breeding biology of the kakerori (''Pomarea dimidiata'') on Rarotonga, Cook Islands” )〕
Since the introduction of the black rat and feral cat adult mortality has more than doubled, a change sufficient to reduce what was previously a highly numerous bird〔 to one of the most endangered birds in the world by the middle 1980s, when the kakerori was listed as one of the highest conservation priorities among all Pacific Island birds.〔(Review of avifauna conservation needs in Polynesia )〕 The removal of rats has made breeding more successful: around two thirds of pairs assisted by a few helpers can now rear both of the normal clutch of two eggs, whereas in the 1980s breeding attempts had a success rate as low as eleven percent.〔 Despite the growth in population, it is still known that a major tropical cyclone could destroy this growth with extreme swiftness, so that conservation work is still very important.
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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