Monarca di Rarotonga

Identificazione

The Rarotonga monarch is an insectivorous passerine which is 10 cm tall, with an adult mass of 20 grams (0.7 oz) for female birds, and 25 grams (0.9 oz) for large male birds. Hunting mainly consists of foraging for insects within foliage, and occasionally taking insects during flight. <p>The Rarotonga monarch is an unusual with regard to its plumage colour, as it is the only bird known to undergo sequential changes in plumage as it grows. Initially, the grey and orange birds were attributed to different species. Later, it was thought that grey plumage birds were male, while the orange birds were females or juveniles of the same species, but this was corrected to being age-based plumage in 1983. The initial plumage of orange to orange-grey changes to pure grey when maturity is reached after four years.

Tassonomia

The Rarotonga monarch was originally described in the genus Monarcha. Alternate names include Cook Island flycatcher, Cook Islands monarch, Kakerori, and Rarotonga monarch-flycatcher.

Nome scientifico

Pomarea dimidiata

Autorità

(Hartlaub & Finsch, 1871)

Ordine

Passeriformi

Famiglia

Monarchidae

Genere

Pomarea

Areale e habitat

Migrazione

Resident species

Comportamento

Owing to its tropical oceanic island location, the Rarotonga monarch is exceptionally long-lived having an adult survival of between 85 and 89 percent, a life expectancy of seven to nine years, and a maximum known lifespan of around 24 years and 8 months. These figures are comparable to large Australian passerines like the superb lyrebird or satin bowerbird and more than ten times the life expectancies of similar sized Holarctic songbirds.<p>The extraordinary longevity of these birds may explain the evolution of helpers at the nest in a family where this feature is otherwise completely absent. Males can breed at one year, but do not do so in practice until they are four years old. Breeding season is between October to February, but most eggs are laid between October and Early November. Nests are mossy deep cups which are built in the fork of a tree branch, often constructed above creeks, and take about 14 days to build. Clutches are 1–2 eggs. In Rarotonga, many nest failures are attributed to predation by black rats or kiore, as birds sit on the nest.<p>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 Rarotonga monarch was listed as one of the highest conservation priorities among all Pacific Island birds. The annual pre-breeding removal of rats (starting in the late 1980s) from its principal breeding area on the south coast of Rarotonga (at the Takitumu Conservation Area) by staff and volunteers has made breeding significantly more successful: around two thirds of pairs assisted by a few helpers can now rear 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, a major tropical cyclone could destroy this population growth with extreme swiftness, so that conservation work is still very important.

Conservazione

Tendenza della popolazione

rising