Justification of Red List Category
This warbler qualifies as Vulnerable because it has a small, declining and fragmented population as a result of habitat loss, potentially compounded by pesticide use and trapping during migration.
The global population is estimated to number a few thousand based on an analysis by BirdLife International (2001). It is estimated to number 2,500-9,999 mature individuals, equating to 3,750-14,999 individuals in total, rounded here to 3,500-15,000 individuals. National population sizes have been estimated at c.50 individuals on migration and c.50 wintering individuals in Taiwan, and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Japan.
A moderate and on-going population decline is suspected owing to habitat change within the breeding grounds, as well as the low number of recent records.
Phylloscopus ijimae is endemic to Japan (BirdLife International 2001). It breeds on the Izu Islands, between Oshima and Aogashima, and was recently discovered nesting on Nakano-shima in the Tokara Islands. There are non-breeding/passage records from Honshu, Kyushu and the Nansei Shoto Islands, where it probably winters. It is also reportedly a regular migrant on the Osumi peninsula in Kagoshima ken (F. Crystal in litt. 2005) and Wakayama-ken (Y. Odaya in litt. 2012). It may also winter in Taiwan (China) (two specimens collected) and the Philippines (one record [several specimens] from Luzon). It has declined markedly since the 1970s.
It occurs mainly in the canopy of deciduous, mixed and evergreen subtropical forests, but also in tangled scrub, alder Alnus thickets and scrub around habitation. Migrants on the Osumi peninsula were seen in evergreen forest at 850-930 m (F. Crystal in litt. 2005). It arrives in the Izu Islands in late March or early April and leaves in late September and October.
It is threatened by habitat loss in the Izu Islands. On Miyake-jima, large areas of natural forest have been replaced with the fast-growing softwood Cryptomeria japonica for timber production. Road construction and developments for tourism are damaging its habitat on Miyake-jima and Mikura-jima. On Mikura-jima, there is a long-term plan to relocate a village, or build a new village at Nango, close to an important nesting area. However, the rate of habitat loss in its breeding range does not appear sufficient to account for its recent decline, suggesting that deforestation in its wintering grounds may also be an important threat. Another contributory factor to its decline may be the increased use of pesticides and other agrochemicals in its breeding range. The eruption in 2000 of Mt. Oyama destroyed or degraded 60% of the forest on Miyake Island, however, the population is thought to have recovered (Y. Odaya in litt. 2012). Further eruptions remain a major threat on Miyake, and there are also active volcanos in the Tokara islands, on the main breeding island of Kuchinoshima and the nearby Suwanosejima island, which currently holds the second biggest population in the chain (F. Crystal in litt. 2012). Trapping may also be a threat for migrants passing the Osumi Peninsula (F. Crystal in litt. 2005), but is not thought to be a major threat (Y. Odaya in litt. 2012).
Conservation Actions Underway
CMS Appendix II. It is legally protected in Japan. The entire Izu Archipelago has been designated as a national park and several important sites have been designated as Special Protected Areas. However, there are no rangers in the national park, and loss and modification of habitats continues on many islands. There is a small sanctuary on Miyake-jima.
10-12 cm. Small, stocky, warbler. Bright olive-green above and white below with a lemon-yellow wash on vent. Long, whitish supercilium with lemon yellow centre; white orbital, split by dark olive-green eye-stripe and lore. Slightly mottled ear-coverts and cheeks. Single whitish wing-bar in most birds. Faint greyish wash to sides of breast and flanks. Yellowish undertail-coverts. pinkish legs and feet; bill dark above, strong yellow below to tip. Similar spp. Arctic Warbler P. borealis is larger, stockier, has yellowish supercilium, cheeks and underparts. Voice A short, bright, silvery swee-swee-swee-swee, and sometimes a slower more disyllabic suwee-suwee-suwee-suwee. Call a loud huee, with a downward inflection.
Text account compilers
Benstead, P., Gilroy, J., Taylor, J., Allinson, T & North, A.
Crystal, F., Allen, D. & Odaya, Y.
BirdLife International (2023) Species factsheet: Phylloscopus ijimae. Downloaded from http://datazone.birdlife.org/species/factsheet/ijimas-leaf-warbler-phylloscopus-ijimae on 07/06/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 07/06/2023.