The Japanese Leaf-Warbler is sized between 12–13 cm in length[4] . They typically have darker green upper body feathers, with an under body (or belly) with lighter green feathers [4]. They have a very short and black (with a hint of yellow) beak, as well as extremely small legs that vary from pale yellow to orange-brown [4]. The bird has a clear yellowish-white eyebrow stripe above the bird's dark eyes[4]. Adults are bright olive-green (with a white wingbar and greenish tail)[4]. Both sexes look alike. Juveniles are roughly similar, yet duller in color (more grey-brown)[4].
Subspecies
Monotypic, only existing form of this species of bird and there are no further subdivisions[4].
General Habitat
This species lives in mixed and deciduous forests, as well as in coniferous woods and thickets[4]. It is usually found between 1500 and 2500 meters in elevation, but most often below 2200 meters. It nests in thick undergrowth, rhododendron bushes, and scrub above the tree line[4]. In winter, it is seen below 1800 meters in woodlands, rainforests, secondary growth, plantations, and gardens[4]. It also occurs in shrublands, wetlands, and cultivated areas, as well as artificial terrestrial habitats[5]. The species depends on thick vegetation for nesting and foraging[5].
Distribution
The Japanese leaf warbler breeds mainly in Japan, from Honshu to Kyushu[4]. In the non-breeding season, it is found in areas such as Taiwan, the Philippines, Borneo, Java, and in small numbers as far east as the Moluccas[4]. It also winters in Brunei, Indonesia, Malaysia, and parts of China[5].
Movements and Migration
The Japanese leaf warbler is a migratory bird[4]. After breeding, it moves south or southwest through eastern China and nearby islands[4]. It spends the winter in Taiwan, the Philippines, Borneo, and Java[4]. Migration takes place from August to November, and the birds return to Japan in mid-May[4]. Arrival often happens within one or two weeks, although timing can be confused with other related species[4].
Diet and Foraging
Its diet is made up mostly of insects and their larvae[4]. Common food items include midges, ants, grasshoppers, caterpillars, beetles, spiders, and small snails[4]. In autumn, it may also eat berries[4]. The warbler usually forages alone or in pairs but can join mixed groups of birds outside of the breeding season[4]. It searches for food in trees, shrubs, and on the ground, and it sometimes catches insects while flying[4].
Sounds and Vocal Behavior
The song of the Japanese leaf warbler is a series of short phrases repeated several times, often lasting 1.5–2 seconds[4]. It is lower in pitch than that of related species such as P. examinandus and has a slower rhythm than P. borealis[4]. Its call is a dry “brrt” sound, which is lower and softer compared to the calls of similar warblers[4].
Breeding
Breeding takes place from June to August, and pairs often raise two broods in a season[4]. The species is mostly monogamous[4]. Males sing to mark their territory, and nests are built on the ground among plants or bamboo[4]. Nests are round and made of moss, stalks, and animal fur, with an opening at the side[4]. The clutch usually contains four to five white eggs with small dark spots[4]. The female incubates the eggs for about 12–13 days, and chicks leave the nest 13–14 days after hatching[4]. Both parents feed the young, though sometimes the female cares for them alone[4]. Nests are often targeted by cuckoos, which lay their eggs inside, and snakes may also prey on them[5].
Conservation status
The Japanese leaf warbler is currently classified as Least Concern on the IUCN Red List (assessed June 12, 2024)[5]. The population trend is considered stable, and there is no evidence of major declines or severe fragmentation[4]. Exact numbers of mature individuals are unknown[5], but it is locally common, with male territory density estimated at 10–30 birds per square kilometer[4]. Its average generation length is estimated at about 2 years[5].
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