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Cettia diphone
(Japanese bush-warbler)

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Datasheet

Cettia diphone (Japanese bush-warbler)

Summary

  • Last modified
  • 13 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Cettia diphone
  • Preferred Common Name
  • Japanese bush-warbler
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Chordata
  •       Subphylum: Vertebrata
  •         Class: Aves
  • Summary of Invasiveness
  • C. diphone is a songbird which is native to Japan, China and Taiwan, and to some other regions of the Far East. Japanese Bush-Warblers have not been introduced anywhere in the world except the main Hawaiian Isl...

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Pictures

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PictureTitleCaptionCopyright
Japanese Bush Warbler (Cettia diphone) adult in habitat.
TitleAdult in habitat
CaptionJapanese Bush Warbler (Cettia diphone) adult in habitat.
Copyright©M.Nishimura - GFDL, CC-BY-3.0
Japanese Bush Warbler (Cettia diphone) adult in habitat.
Adult in habitatJapanese Bush Warbler (Cettia diphone) adult in habitat.©M.Nishimura - GFDL, CC-BY-3.0

Identity

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Preferred Scientific Name

  • Cettia diphone Kittlitz

Preferred Common Name

  • Japanese bush-warbler

Other Scientific Names

  • Horornis diphone Kittlitz
  • Sylvia diphone Kittlitz

International Common Names

  • English: Chinese bush-warbler; Japanese nightingale; oriental bush-warbler; short-winged reed-warbler; singing bush-warbler
  • Spanish: cetia japonés; ruiseñor bastardo japonés
  • French: bouscarle chanteuse

Local Common Names

  • Germany: Japanbuschsänger
  • Japan: uguisu
  • Netherlands: Japanse struikzanger

Summary of Invasiveness

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C. diphone is a songbird which is native to Japan, China and Taiwan, and to some other regions of the Far East. Japanese Bush-Warblers have not been introduced anywhere in the world except the main Hawaiian Islands, where they were released on O'ahu on repeated occasions during the years 1929-1941 (Caum, 1933; Long, 1981; Lever, 1987; Pyle and Pyle, 2009). The birds were initially introduced to control insects, but several other releases on O’ahu, totaling approximately 138 individuals, were made by the Honolulu Mejiro Club and Hui Manu Society for aesthetic purposes (Caum, 1933; Hawaiian Audobon Society (HAS), 1967; Swedberg 1967; Pyle and Pyle, 2009). C. diphone was first noted on the other islands between 1979 and 1980, and it currently inhabits all of the high Hawaiian islands (Kauai, Oahu, Lanai, Molokai, Kahoolawe, Maui and Hawaii)  (Pratt et al.; 1987; Nelson and Vits; 1998; Pyle and Pyle, 2009); Hamao, 2014). It can now be found in many of the native forests, which may well pose a further threat to Hawaii's endemic forest species, perhaps especially by competing for food (Foster, 2009; Pyle and Pyle, 2009).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Chordata
  •             Subphylum: Vertebrata
  •                 Class: Aves
  •                     Order: Passeriformes
  •                         Family: Sylviidae
  •                             Genus: Cettia
  •                                 Species: Cettia diphone

Notes on Taxonomy and Nomenclature

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The currently accepted scientific name for the Japanese Bush-warbler is C. diphone (Kittlitz, 1830), previously known as Horornis diphone. Seven subspecies are currently recognized (Alström et al., 2011):

C. diphone diphone (Kittlitz, 1830)
C. diphone cantans (Temminck & Schlegel, 1847)
C. diphone canturians (Swinhoe, 1860)
C. diphone borealis (Campbell, 1892)
C. diphone restrictus (Kuroda, 1923)
C. diphone riukiuensis (Kuroda, 1925)
C. diphone sakhalinensis (Yamashina, 1927)

C. diphone canturians is also known as Manchurian Bush-warbler, which has been considered a separate species on basis of differences in plumage and voice; further study, including DNA analysis, is required (Clement and Juana, 2013). The subspecies C. diphone borealis is often called Korean Bush-warbler. C. diphone sakhalinensis living in the south of the Kuril Islands is also called C. diphone viridis. C. diphone is sometimes treated as conspecific with Cettia seebohmi.

Although C. diphone does not sing at night, the beauty of its song led to it being given an English name of the Japanese Nightingale. 

Description

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Both male and female birds are olive brown or slightly dark brown on the upper part and dirty white or beige on the underpart. They have creamy superciliaries. The plumage coloration varies slightly between the subspecies or the local populations (Hamao, 2007; 2014). One form, the brown form, is characterized by having deep rusty brown, or red-brown (Hamao, 2014) upper parts (C. d. restricta), while the other, gray form, has grayish olive upper parts (C. d. riukiuensis) (Kajita et al., 2002). The subspecies C.d. diphone has a rufous-brown forehead and crown and a yellowish white underpart (Yamashina, 1941; Hamao, 2014). The immature birds are similar but are browner above and may exhibit narrow wing bars, caused by buffy tips to the feathers. The bill and legs of C. diphone are pale coloured.

Total length of the Japanese bush-warbler is approximately 14-15.5 cm (Yoshii, 1988; Hamao, 2007; 2014). The length of wing in the male is 62.2-67.7 mm and in the female is 51.3-57.0 mm. The tail length in the male is 64.8-73.1 mm and in the female is 53.4-60.7 mm. The length of the culmen in the male is 10.6-13.8 mm and in the female is 9.9-11.7 mm. The tarsus length in males is 24.5-27.1 mm and in the female is 21.4-23.2 mm. The weight is approximately 14.8-22.3g in males and 10.0-13.7g in females (Hamao, 2007; 2014).

Some subspecies show sexual dimorphism (Emura et al., 2013). Songs of male Japanese bush-warblers are classified into two types. One is a type-H song that sounds as "Hoh, hokekyo" and the other is a type-L song that has intermittent whistles as “Hoh-hohohokekyo”. The type-L song is assumed to function as a threat to rivals in the vicinity because territory owners frequently use this type in the periphery of their territory and they return this type of song to replayed songs of other males (Momose, 1986; Hamao, 2007; 2014). The "Taniwatari" call is often assumed to be an alarm, but males sometimes utter this call responding to the "Chee, chee" call of females, and sometimes start this type of call immediately after the type-L song, repeating a combination of these songs and calls for a long period of time (Hamao, 2007).

Distribution

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C. diphone was first described in 1830 by von Kittlitz, who observed the bird in the Bonin Islands. Japanese Bush-warblers are distributed throughout the main islands of Japan and also on small peripheral islands (Hamao, 2013). Japanese Bush-warblers are generally distributed in northeastern China, the Russian Far East, the Korean Peninsula, the Hawaiian Islands and Japan (Hamao, 2007, 2014).

Distribution of the subspecies is listed below:

C. diphone diphone – Endemic from the Ogasawara Islands, consisting of the Bonin (Mukojima, Chichijima, and Hahajima groups: 26° 32’-27° 43’N, 142°05’-142° 14’E) and Volcano Islands (24° 23’-25° 45’N and 141° 24’-141° 47’E), subtropical oceanic islands located approximately 1000 km south of mainland Japan. Although C. d. diphone was widely distributed throughout the Ogasawara Islands until the 1930s, the species has been extirpated on several islands (Momiyama, 1930; Yamashina, 1930; Emura et al., 2013). Specifically, the species has recently disappeared from the islands of the Mukojima group, Kita-iwoto and Iwoto of the Volcano Island, and probably some satellite islands of the Chichijima group (Tokita and Watanabe, 2001; Kawakami et al., 2008; Kawakami et al., 2009; Emura et al., 2013). The subspecies can also be found on the south of the Iza Islands (Clements et al., 2014)

C. diphone cantans - Widely distributed in the main islands of Japan (Hamao, 2007; 2014). Also occurs in the Izu Islands, and other islands, as well as on the peripheral or oceanic islands, including coastal islands south to Yaku-shima, Tanega-shima and Hachijo-jima, also Tsushima and Quelpart I (Cheju-do) (Clements et al., 2014) and Honshu Island (Hamao, 2014). The subspecies has also been observed in spring almost every year since 2007 on Mukojima (Emura et al., 2013). Also on Daito Islands, which are located within subtropical Japan, a few migrant birds of this subspecies have colonized and a new population has established since the 1990s, following the extinction of C. d. restrictus in the 1920s in that area (Anezaki et al., 2003; Takagi, 2009; Emura et al., 2013).

According to Clements et al. (2014) this subspecies was the one introduced in Hawaii. It was released on O'ahu in 1929-1941 (Caum, 1933; Long, 1981; Lever, 1987; Pyle and Pyle, 2009) and has since spread naturally to most or all other major islands of Hawaii (Pyle and Pyle, 2009).

C. diphone canturians – During the winter, this subspecies occurs in south and southeastern China, Taiwan, northeastern India, Assam, northwestern Thailand, north and central Indochina, and the northern Philippines. Breeds in central and eastern China, Gansu and Sichuan east to Anhui and Zhejiang (Clement and Juana, 2013; Clements et al., 2014).

C. diphone borealis - Often called Korean Bush-warbler, occurs during the winters in southeastern China, Fujian, Taiwan and N Philippines, Batan Is, Luzon (Clement and Juana, 2013). Breeds in northeastern China, adjacent southeastern Siberia, south Ussuriland, and Korea (Clements et al., 2014). This subspecies is considered an irregular visitor to Japan from the continent (Hamao, 2014).

C. diphone restrictus – Endemic subspecies that occurred only on Minami-Daitojima Island, this subspecies has been regarded as extinct in that area since the 1920s (Anezaki et al., 2003; Takagi, 2009; Emura et al., 2013). However, in recent years, two types of Japanese Bush Warblers were observed on Okinawajima Island, including one with features of C. d. restrictus (Kajita et al., 2002). This subspecies is alive in Amami and Ryukyu Islands (Hamao, 2007; 2014). The bird is also found in the Nansei Islands (Hamao, 2007; 2014) and in the Ryukyu Islands (Hamao, 2014).

C. diphone riukiuensis – Occurs in the Ryukyu Islands, from Amami-o-shima south to Iriomote-jima (Clement and Juana, 2013) and in the Sakishima Islands (Gordo and Doi, 2012). C. diphone with the characteristics of this subspecies has also been observed on Okinawajima Island and appears only in winter (Kajita, et al., 2002). Therefore, it probably breeds in the northern area (Hamao, 2007; 2014).

C. diphone sakhalinensis- During the winter, in the non-breeding season, occurs in southeastern China (Clements et al., 2014). Breeding occurs in the south Sakhalin and south Kuril Islands (Kajita et al., 2002; Emura et al., 2013; Hamao, 2007; 2014). The individuals that breed in the Kuril Islands are also known as C. diphone viridis.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaPresentNative Not invasive Clement and Juana, 2013; Clements et al., 2014
-AnhuiLocalisedClement and Juana, 2013; Clements et al., 2014Subspecies C.d. canturians breeds in the area
-GansuLocalisedClement and Juana, 2013; Clements et al., 2014Subspecies C.d. canturians breeds in the area
-SichuanLocalisedClement and Juana, 2013; Clements et al., 2014Subspecies C.d. canturians breeds in the area
-ZhejiangLocalisedClement and Juana, 2013; Clements et al., 2014Subspecies C.d. canturians breeds in the area
IndiaPresentNative Not invasive Clement and Juana, 2013; Clements et al., 2014Subspecies C.d.canturians occurs in northeastern India during the winter
-AssamPresentNative Not invasive Clement and Juana, 2013; Clements et al., 2014Subspecies C.d.canturians occurs during the winter
JapanWidespreadNative Not invasive Hamao, 2007; Emura et al., 2013; Clements et al., 2014Subspecies C. diphone diphone is endemic from the Ogasawara Islands, consisting of the Bonin and Volcano Islands, located approximately 1000km south of the mainland Japan
-HonshuPresentHamao, 2014Subspecies C. diphone cantans occurs in this island
-Ryukyu ArchipelagoPresentKajita et al., 2002; Hamao, 2007; Clement and Juana, 2013
Korea, DPRPresent Not invasive Clements et al., 2014C. diphone borealis, often called Korean Bush-warbler, breeds in Korea
PhilippinesPresentNativeClement and Juana, 2013; Clements et al., 2014C. diphone borealis occurs during the winters in the Philippines, Batan Island and Luzon. The subspecies C. diphone canturians during the winter occurs in the northern Philippines
TaiwanPresentNativeClement and Juana, 2013; Clements et al., 2014C. diphone borealis and C. diphone canturians occur during the winters in Taiwan.
ThailandPresentNativeClement and Juana, 2013; Clements et al., 2014The subspecies C. diphone canturians occurs during the winter in northwestern Thailand

North America

USAPresentPresent based on regional distribution.
-CaliforniaLocalisedIntroducedInvasive Species Council of California, ISCCCettia diphone appears in the Invasive Species List and Scorecards for California but no additional information is given so it is unclear as to if it is present
-HawaiiPresentIntroduced Invasive Pratt et al., 1987; Nelson et al., 1998; Hamao, 2014

Europe

-Russian Far EastPresentHamao, 2007; Hamao, 2014For the subspecies C. diphone sakhalinensis breeding occurs in south Sakhalin. C. diphone borealis appears in the Russian Far East

History of Introduction and Spread

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Japanese Bush-Warblers were released on O'ahu in the Hawaiian islands in 1929-1941 (Caum, 1933; Long, 1981; Lever, 1987; Pyle and Pyle, 2009). C. diphone was initially introduced to control insects, but several other releases on O’ahu, totaling approximately 138 individuals, were made by the Honolulu Mejiro Club and Hui Manu Society for aesthetic purposes (Caum 1933; Swedberg, 1967; Berger, 1972; 1975; 1981; Pyle and Pyle, 2009). The bird was first noted on the other islands between 1979 and 1980, and it currently inhabits many of the Hawaiian Islands (Pratt et al., 1987; Nelson and Vits, 1998; Hamao, 2014).

A major dispersal event from O’ahu appears to have occurred in the late 1970s and the early 1980s, when records were first encountered on the four closest islands (Lever, 1987; Pyle and Pyle, 2009). On Kaua'i, the birds were first observed in the Wailua River Valley on February 22, 1983 and by the 1990s they were increasingly found throughout central portions of the island (Denny, 1999; Pyle and Pyle, 2009). They went unrecorded during surveys in 1994 (Walther, 1995; Pyle and Pyle, 2009) but were common by 2000, when the estimated population in the study area was >2000 birds (Foster et al., 2004; Pyle and Pyle, 2009). R.L. Pyle reported the first observations on Molokai, at the head of Pelekunu Valley, on 11 April and 25 May 1979. By 1979-1980 the species was well established on Olokui Plateau and surrounding cliffs and was noted to be increasing rapidly following the survey (Carothers and Hansen, 1982; Scott et al.,1986; Pyle and Pyle, 2009). By 1988 C. diphone was noted very commonly throughout montane areas, and by the 2000s it was described as the most common songbird in E. Moloka'i (Pratt, 2002; Pyle and Pyle, 2009).

On Lana'i, the first record was of a bird heard singing in Hauola Gulch on 4 and 8 April 1980 (P. Conant 1980; E 41:77). Subsequent observers have continued to record moderate numbers in upland areas of Lana'i through the 2000s (Pyle and Pyle, 2009). The first Japanese Bush-Warbler on Maui was heard on the north slope of Mt Haleakala on July 6, 1980 (Carothers and Hansen, 1982; Pyle and Pyle, 2009). By the late 1980s the species had spread at least as far as Ko'olau Gap and Waikamoi Preserve on the west slopes of Mt Haleakala, as well as the west Maui Mts, where it was first detected in June 1984 and described as "abundant" by 1989 (Pyle and Pyle, 2009).

Little has been published on the subspecies of Japanese Bush-warbler introduced to Hawaii, but the specimen evidence (PP examination) indicates it is most likely of the subspecies C. diphone diphone, the most widespread subspecies in Japan and the most likely to be captured for exportation (Pyle and Pyle, 2009). However, Clement and Juana (2013) and Clements et al. (2014) report that the subspecies introduced in Hawaii was C. diphone cantans. Hamao (2014) says that the birds which were introduced to Hawai‘i appear to belong to the subspecies sakhalinensis and/or cantans.

Populations have expanded into native habitats that range from lowland rainforest to subalpine dry forest, even as some native and introduced species have declined (Banko et al., 2013). 

C. diphone appears in the Invasive Species List and Scorecards for California (Invasive Species Council of California, 2014), but no additional information is given.

 

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Hawaii Japan 1929-1941 Biological control (pathway cause) ,
Ornamental purposes (pathway cause)
Yes No Berger (1972); Berger (1975); Berger (1981); Pyle and Pyle (2009); Swedberg (1967) The Japanese Bush-warbler was initially introduced to control insects, but several other releases on O’ahu, totaling approximately 138 individuals, were made by the Honolulu Mejiro Club and Hui Manu Society for aesthetic purpose

Risk of Introduction

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According to the Kaua’i Forest Bird Recovery Project, C. diphone has managed to spread and establish populations in the high-elevation forests and other areas, which may well pose a further threat to Hawai'i's endemic forest species, perhaps especially as competition for food (Pyle and Pyle, 2009) and nesting habitat. 

Habitat

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C. diphone is a native of the Ogasawara Islands, which are subtropical oceanic islands (Emura et al., 2013). The habitat of C. diphone is dense bamboo thickets and shrubs at the forest edge and forest floor (Nakamura and Nakamura, 1995; Hamao et al., 2008). Japanese bush-warblers especially prefer bushes at the forest edge and in open areas of forests from the montane belt to the subalpine zone, though they are widely distributed in dense thickets of bamboo grass and bushes from coastal areas to alpine regions. In recent years, they have more frequently bred in hills and lowlands probably because bushy habitat has increased in flood-controlled river basins and abandoned farmland (Hamao, 2007; 2014). Thickets of Pleioblastus chino bamboo are common around cultivated fields, providing nesting habitat for the warblers (Hamao, 2013). C. diphone places its nests on the crossings of bamboo stems and selected places of high stem density (Amano and Eguchi, 2002).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
 
Terrestrial ‑ Natural / Semi-naturalNatural forests Principal habitat Natural
Natural grasslands Principal habitat Natural
Scrub / shrublands Principal habitat Natural
Littoral
Coastal areas Secondary/tolerated habitat Natural

Biology and Ecology

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Reproductive Biology

Differences in song structure between related species contribute to reproductive isolation between them, because vocalization is a recognition cue between species (Hamao et al., 2008). Birds can avoid heterospecific matings by discriminating between songs of conspecifics and heterospecifics (Hamao et al., 2008). C. diphone males sing a loud "Hoh,hokekyo" with the accent on the “ke” of the second syllable, and shriek like "Pirrrrrr-kekkyo, kekkyo...", which is called "Taniwatari (valley crossing call)". Males also sing the same song but in a whispering voice when they court females. Females whisper "Chee, chee" softly during the incubation and nestling periods (Hamao, 2007; 2014).

In early spring, males begin to sing in wintering sites. Most, if not all, birds migrate to highland areas and breed in bamboo bushes or grass meadows. Males sing from late March to August in the breeding area and immigrate back to the wintering area in September to October (Wada and Shimizu, 2003). Male bush warblers wintering at lower elevation arrive in late March and establish territory after territorial dispute. Thereafter, a male advertises his ownership by singing, but actual fighting is rare (Wada and Shimizu, 2003). Male bush warblers are very territorial and hold territory during the whole breeding season defending it with territorial songs. Males may have more than one nest on their territories at the same time if the resources are abundant, indicating a polygynous breeding strategy (Wada and Shimizu, 2003). It is known that a single male breeds with two females or more in his territory. There is a record of a male that mated with six or seven females one after another in the same breeding season (Hamao, 2007; 2014).

Females arrive later, in early April to mid-April and mate with the owner of a territory (Wada and Shimizu, 2003). Male-female interaction is very rare, including parental care. The male does not participate in nest building, incubating, or feeding of young (Haneda and Okabe, 1970) and remains reproductively active until mid-August. While males are singing, females build a nest in April to early May and lay eggs (Wada and Shimizu, 2003). They build a rugby ball-shaped nest with an opening on the side or the upper side using primarily dead leaves of bamboo grass. The nest is often built in a low place within bushes. They usually lay 4-6 eggs, which are chocolate brown in colour. The incubation and nestling periods are about 15 and 13 days, respectively. The fledging rate is low, such as 27%, due largely to predation (Hamao, 2007; 2014). Female’s brood patch is maximum in late May to early June indicating that females are incubating around this time.

Although the bush warbler is polygynous and males provide no parental care, they do mate-guard when a potential mate is receptive (Wada and Shimizu, 2003). Females attempt to breed again with other males after they have fledged their young successfully or lost their eggs or nestlings due to predation (Hamao, 2007; 2014). These stages roughly correspond to April through May. After the female is incubating and no longer receptive, the male may shift his territory slightly and try to attract another female (Wada and Shimizu, 2003). Unlike other subspecies, both male and female C.d. diphone feed the chicks (Ueda et al., 1992; Emura et al., 2013).

Physiology and Phenology

During 1953-1979, first records of singing males of C. diphone on the subtropical Ryukyu and Sakishima Islands were markedly delayed. Those bird populations from sites with the largest increases in human population showed the greatest delays in their first singing or arrival dates. Indirect evidence shows that bird population declines were the most plausible origin for the latent delay of phenology. During 1979-2005, heterogeneity among populations was marked, with both delayed and advanced first records of singing. The earlier and later dates counterbalanced each other and precluded any statistically significant temporal trend for the whole set of populations.

C. diphone is detected earlier in response to warmer springs. There are significant differences in the sensitivity to temperatures among populations. C. diphone has earlier records in warm years, but does not show a consistent tendency of advanced arrivals in recent decades, in spite of the notable increase in temperatures in Japan (Gordo and Doi, 2012a,b).

Japanese bush warbler, C. diphone riukiuensis, from the subtropical Ryukyu and Sakishima Islands, has been studied for the period 1953–2005. Overall, males are singing 13 days later during the last five decades. Temperature increased in the study sites during the study period and most populations showed a negative effect of temperature before singing season. This apparently contradictory phenological response to climate change may be further evidence of the population declines detected in the endemic species of the small southern islands of Japan as a result of habitat loss and degradation (Gordo and Doi, 2012b).

Nutrition

According to Clement and Juana (2013) in the Handbook of the Birds of the World the diet of C. diphone is not well known, but is presumed to be mainly larval and adult invertebrates. It is also known to forage for fruits and berries to supplement its diet.

Associations

Japanese bush-warblers are parasitized by Lesser Cuckoos, Cuculus poliocephalus; the cuckoo lays chocolate-brown eggs that resembles those of this host in colour (Kiyosu, 1965; Higuchi, 1987). The brood parasitism is principally responsible for breeding failure in nests where the eggs are laid after June when Lesser Cuckoos arrive. Hosts parasitized by other Cuculus cuckoos often eject a parasite egg or abandon their nest, but Japanese bush-warblers are not reported to reject parasitized eggs. Japanese bush-warblers are also parasitized by Oriental Cuckoos, Cuculus optatus, in Hokkaido, northernmost Japan, where Lesser Cuckoos are rare (Hamao, 2007; 2014). 

Climate

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ClimateStatusDescriptionRemark
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Preferred Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
18-60

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Cuculus optatus Parasite Adults to species
Cuculus poliocephalus Parasite Adults to species

Notes on Natural Enemies

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Japanese bush-warblers are parasitized by Lesser Cuckoos, Cuculus poliocephalus. The cost of brood parasitism is reduced by starting to breed before the arrival of Lesser Cuckoos. Japanese bush-warblers are also parasitized by Oriental Cuckoos, Cuculus optatus, in Hokkaido, northernmost Japan (Hamao, 2007; 2014).

In Japan, the introduced Red-billed Leiothrix, Leiothrix lute has also invaded broadleaved deciduous forest. This species is dominant over the avifauna of broadleaved deciduous forest; major species occupying a similar niche to this species include C. diphone (Eguchi and Amano, 2004).

Means of Movement and Dispersal

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Natural Dispersal

Japanese Bush-warblers are generally distributed in northeastern China, the Russian Far East, the Korean Peninsula and Japan, migrating within the region between winter and summer. It is assumed that they move to the lowlands of a temperate region in winter (Hamao, 2007; 2014).

Intentional introduction

C. diphone was systematically introduced to O’ahu, Hawaiian Islands, multiple times by the territorial (now state) government and Hui Manu, a private group that imported song birds (Caum, 1933; Hamao, 2014). The birds have since dispersed to other Hawaiian islands.

Impact Summary

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CategoryImpact
Cultural/amenity Positive
Environment (generally) Positive and negative

Environmental Impact

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Concerns have been expressed about competition of bush-warblers with native species, perhaps especially as food competitors (Foster, 2009; Pyle and Pyle, 2009). According to the Kaua’i Forest Bird Recovery Project, C. diphone has managed to establish populations in the high-elevation forests of Hawaii where it may compete with native birds for food and nesting habitat. The Maui Forest Bird Restoration Project states that it is not known what pressures this species will exert on Maui's native forest birds as it continues to expand.

Reed et al. (2012) suggest that evidence for competition to threatened and endangered species in Hawaii from exotic birds such as C. diphone is controversial and not well established. According to BirdLife International, C. diphone is presented as a possible threat to Nukupuu Hemignathus lucidus, which is historically present in Haleakala and Kaua’i Forest and Uplands, Hawaii, but has not been recorded since 1996 (Birdlife International, 2015b). However, as the nukupuu was nearly extinct before the bush-warbler arrived on Kaua'i and Maui, the warbler is unlikely to have had any significant impact (Paul Banko, personal communication). C. diphone is also listed as a potential competitor in the Kaua’i montane forest to Puaiohi, Myadestes palmeri (Birdlife International, 2015c).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Hemignathus lucidus (Nukupuu)CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered)HawaiiCompetitionBirdLife International, 2015b
Myadestes palmeri (Puaiohi)CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered)HawaiiCompetitionBirdLife International, 2015c
Loxioides bailleui (palila)CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered speciesHawaiiCompetition - monopolizing resourcesUS Fish and Wildlife Service, 2006
Oreomystis bairdi (akikiki)CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered speciesHawaiiCompetition - monopolizing resourcesUS Fish and Wildlife Service, 2006

Social Impact

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The song of C. diphone is regarded in Japan as heralding the start of spring. Its role in signifying spring has led to it being frequently used in poetry and art in Japan.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly mobile locally
  • Fast growing
  • Has high reproductive potential
Impact outcomes
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Competition - monopolizing resources
  • Competition
  • Interaction with other invasive species
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately
  • Difficult to identify/detect in the field

Uses

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The guano of C. diphone has been used for centuries by geishas and kabuki actors in Japan to clean off make-up, and as a skin cream. It is now used in spas as a facial treatment. The powder, collected from caged birds, is usually mixed with rice bran (which helps mask the musky smell) or combined with white clay.

C. diphone has been kept as a caged bird for its song.

Similarities to Other Species/Conditions

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Cettia seebohm is similar to C. diphone in morphology and plumage, although slight differences occur in plumage colour (Hamao et al., 2008), wing shape, and male body size (Hamao et al., 2008). It is endemic to northwestern Luzon, Philippines (Hamao et al., 2008). The Japanese Bush-warbler seems to have very similar niches with other species, for example the Red-billed Leiothrix, Leiothrix lute, which results in a change in the nest site selection and the nest height when they coexist (Eguchi and Amano, 2008). According to BirdLife International, C. diphone resembles a similar species to Kaua’i Elepaio, Chasiempis sclateri in its endemic habitat in Kaua’I (Birdlife International, 2015a), but C. diphone is duller, with prominent eyebrows and no white markings.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention of entry, through legislation and enforcement to prevent importation, is far more effective than control of introduced bird species, which can only work during incipient invasion. Methods used to manage invasive bird populations are similar to those used for mammals: traps (with or without live bird decoys), shooting, exclusion, and limited use of toxicants (Avery and Tillman, 2005). The exceptions are that egg and nest destruction is sometimes used with birds and frightening devices are often used to protect relatively small areas (Witmer et al., 2007). For the most part, current methods are adequate to address problems attributed to invasive bird species. The major issue is that wildlife managers are often not free to apply the most effective techniques to solve problems caused by invasive species. The constraint is particularly prominent in situations that involve lethal control measures (Avery and Tillman, 2005).

Gaps in Knowledge/Research Needs

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Several gaps in knowledge still remain: genetics, nutrition and environment requirement, impact on other species and habitat in the territory invaded. Little or no information is available on possible competitive effects of the Japanese bush-warbler in Hawaii (Fiedler and Kareiva, 1998; Reed et al., 2012).

C. diphone canturians, also known as Manchurian bush-warbler, has been considered a separate species on basis of differences in plumage and voice; further study, including DNA analysis, is required (Clement and Juana, 2013).

References

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Links to Websites

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WebsiteURLComment
BirdLife Internationalhttp://www.birdlife.org
Handbook of the Birds of the World Alivehttp://www.hbw.com

Organizations

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USA: Kaua’i Forest Bird Recovery Project, 3751 Hanapepe Rd, Hanapepe, HI 96716, Hawaii, http://kauaiforestbirds.org

USA: Mau’i Forest Bird Recovery Project, 2465 Olinda Road, Makawao, 96768-7138, Hawaii, http://www.mauiforestbirds.org/

Contributors

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27/04/15 Original text by:

Eduado Ventosa, Puerto Rico Dept. of Natural and Environmental Resources, Puerto Rico

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