Classified as Vulnerable (VU) on the IUCN Red List 2007 (1).
The global population is estimated to be in the band c.2,500-9,999 mature individuals (BirdLife International 2001), equivalent to 3,750-14,999 individuals, rounded here to 3,500-15,000 individuals. The population in Japan has been estimated at c.100-10,000 breeding pairs (Brazil 2009). Population Trend
Nest-predation by Siberian weasels Mustela sibirica,
Large-billed Crow Corvus macrorhynchos
and domestic cats is the main threat. Its population on Miyake-jima declined rapidly following the introduction of Siberian weasels in the 1970s. The population of Large-billed Crow on Mikake-jima and the other Izu Islands has increased as a result of the dumping of raw garbage. During a survey on Miyake-jima in 1992, a total of 22 nests were found containing eggs, all of which hatched, but all nestlings were subsequently predated. The effects of predation are likely to have been compounded by habitat loss, associated with timber production, tourist developments and road construction. Volcanic eruptions on Miyake-jima in 2000 had a negative effect on the population on that island (Y. Yamamoto in litt.
The Siberian weasel, Mustela sibirica, which was introduced onto Miyake-jima Island, preys on eggs and chicks in the nest, and appears to have caused a significant decline in the number of Izu thrushes. Nest predation by large-billed crows, Corvus macrorhynchos, has also increased due to raw garbage becoming a more familiar sight in the Izu Islands, and domestic cats also prey on nests and fledglings. The impact of predation has been compounded by the ubiquitous threat of habitat loss. On many of the Izu Islands, natural forest has been destroyed for timber production, road construction and tourism development (3) (4). An additional, natural threat is volcanic eruptions on Miyake-jima. An eruption in 2000 covered the island in a fine layer of ash, killing many forest-dwelling insects. This does not appear to have affected the Izu thrush to the same extent as other birds on the island, but the emission of deadly gases from the volcano crater could still prove to have a damaging effect on Izu thrush populations (3).
Conservation Actions Underway
It is legally protected in Japan. The entire Izu Archipelago has been designated as a national park and several important sites as Special Protected Areas. There is a small sanctuary on Miyake-jima. A recent awareness campaign has been carried out (Y. Yamamoto in litt.
2012).Conservation Actions Proposed
Research its ecology, especially the migratory movements of the Tokara Islands population. Maintain and enhance areas of suitable forest and woodland on the Izu Islands. Plan new development on the Izu Islands to minimise their negative effects on the habitats of this and other endemic species. Strengthen the infrastructure and human resources of the national park on the Izu Islands to improve enforcement of habitat conservation measures. Control predators, particularly Siberian weasel and Large-billed Crow. Instigate new controls on the dumping of garbage to reduce the numbers of Large-billed Crow.
The Izu thrush is on the Red List of Japan, which means that its conservation importance is recognised (3). The Izu Islands lie within the Fuji-Hakone-Izu National Park (5), and several places have been designated as “special protected areas”, but there are no park rangers, and the destruction and alteration of habitat continues on many of the islands (4). The maintenance of suitable forest habitat is important for the conservation of the Izu thrush, and thus enforcement of the National Park is essential. This is required in addition to the control of predators, for example, by introducing new controls on the dumping of garbage to reduce the numbers of large-billed crows (3).