Ijima's leaf warbler (Phylloscopus ijimae) (also known as Izu leaf warbler, Ijima's willow warbler or Ijima's warbler) is a species of Old World warbler in the family Phylloscopidae. The species is native to Japan, where it has been designated a Natural Monument under the 1950 Law for the Protection of Cultural Properties,^[6] with records also from Taiwan and the Philippines.^[1]

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Ijima's leaf warbler
Warbler in Taiwan (April 2021)
Conservation status
Vulnerable  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Family:	Phylloscopidae
Genus:	Phylloscopus
Species:	P. ijimae
Binomial name
Phylloscopus ijimae (Stejneger, 1892)
Synonyms
Acanthopneuste ijimae (protonym)[2] Acanthopneuste occipitalis ijimae[3] Phylloscopus coronatus ijimae[4] Phylloscopus tenellipes ijimae[5]

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Ijima's leaf warbler is a monotypic species first described by Leonhard Stejneger in 1892, based on three specimens collected in the spring of 1887 by Namie Motokichi [ja] on Miyake-jima and Nii-jima, in the Izu Islands of Tokyo.^[2] Initially given the scientific name Acanthopneuste ijimae by Stejneger,^[7] Momiyama Tokutarō [fi] followed suit in a 1923 paper on the birds of Izu Ōshima.^[8]: 206 In a 1926 paper on a collection of birds from the Ryūkyū Islands, Kuroda Nagamichi treated the warbler instead as a subspecies of the western crowned warbler, as Acanthopneuste occipitalis ijimae,^[3]: 85 Yamashina Yoshimaro following suit in 1935.^[9]: 431 In 1938, Claud Ticehurst treated the warbler as a "race" of the eastern crowned warbler (Phylloscopus coronatus),^[5][10] as did Allan Robert Phillips in 1947, based on three specimens from the southern part of Okinawa Island, the combination being Phylloscopus coronatus ijimae.^[4] In 1953, citing differences in songs and nesting behaviours, Oliver L. Austin and Kuroda Nagahisa elevated the warbler to specific rank, with the binomial Phylloscopus ijimae,^[11]: 543 a treatment followed the next year by Charles Vaurie^[12]: 22 Kenneth Williamson treated the warbler as a subspecies of the pale-legged leaf warbler, under the combination Phylloscopus tenellipes ijimae;^[5] however, due to differences in its vocalizations, nesting preferences, and DNA,^[7] the warbler has again been elevated to species rank, as Phylloscopus ijimae.^[13] The specific name honours Ijima Isao, for his contributions to Japanese ornithology.^[2][14]

Ijima's leaf warbler is a small passerine with a total length of 11.5 cm (4.5 in) and weight of around 10 g (0.35 oz).^[16] The crown and nape are a greenish-grey, upperparts a bright olive green, flanks greyish, and underparts white.^[7] It has a long white or buffish-white supercilium, blackish eyestripe, and dark brown iris.^[7] The beak is relatively long and "broad-based", the upper mandible dark brown, the lower yellowish, and the legs and feet a pinkish brown.^[1][7]

The warbler is similar in appearance to the eastern crowned warbler (Phylloscopus coronatus), from which it may be distinguished visually by the absence of a central stripe on its crown and by its paler yellow undertail coverts.^[7][15] Its song and calls, which include "swss, swss, swss", "swee-swee-swee-swee-swee", "shwee-it, shweet, shweet, shweet", and a soft "se-chui, se-chui, se-chui" and "phi-phi-phi",^[7] also differ from those of the eastern crowned warbler.^[17]

Ijima's leaf warbler breeds in the summer in the Izu Islands, from Izu Ōshima to Aogashima, and also on Nakanoshima in the Tokara Islands.^[16][18] In the spring and autumn, there are records of its presence from Honshū (Shizuoka, Aichi, and Wakayama prefectures), Mizunoko-jima, Tanegashima, Yakushima, and Okinawa Island and the Yaeyama Islands in the Ryūkyūs.^[16][18] Its wintering grounds are poorly understood; a small number may overwinter in the Izu Islands (Miyake-jima and Hachijō-jima^[17]) and Ryūkyū Islands, while there are also records from Taiwan and Luzon in the northern Philippines.^[15][18] It inhabits the "lowland deciduous and mixed subtropical evergreen forest" and laurel forest, including the forest edge, stands of alder (Alnus) and bamboo, and shrubland.^[15][18]

Insects form the principal component of its diet — when written in kanji (飯島虫喰),^[17] the warbler's Japanese name reads as "Ijima's insect-eater" — which also includes seeds.^[18] For these it forages, singly or in small groups (sometimes including other species, in particular long-tailed tits (Aegithalos caudatus)), on lower branches, in the forest canopy, and on the ground, and it may also take prey in mid-air.^[18][19]

The breeding season is from April to June or July.^[16][18] Nests are built some 0.5–2 m (1 ft 8 in – 6 ft 7 in) from the ground,^[7] on broad-leaved trees and in bamboo (this nesting behaviour differs from that of the eastern crowned warbler, which nests on the ground and in earthen banks).^[18] The clutch size ranges from two to four eggs, with three or four the most common.^[18]

The declining population, thought to total fewer than 10,000 individuals,^[1] is threatened by habitat loss and fragmentation.^[7][15] In addition, the availability of prey may be impacted by the use of pesticides.^[18] The species was badly affected by the eruption of Miyake-jima in 2000.^[18]

With an estimated 3% of the global population, Phylloscopus ijimae (Chinese: 飯島柳鶯) is included on the 2016 Red List of Birds of Taiwan with the status "vulnerable".^[20]: 38 (The species is also included on the 2016 Red List of China's Vertebrates (with the vernacular name 日本冕柳莺), with the status "near threatened".^[21]: 523) In the Philippines, the species is included on the National List of Threatened Fauna, as a migrant bird on Luzon, with the status "vulnerable".^[22] On the 2020 Japanese Ministry of the Environment Red List, Phylloscopus ijimae (Japanese: イイジマムシクイ) has the status "vulnerable",^[23] as it had done also on the 1998 and 2007 editions.^[16]

• List of birds of Japan
• List of Red Lists