Bird Research News

Vol.5 No.5

2008.5.15.

Styan's Grasshopper Warbler Uchiyama-Sennyu (Jpn) Locustella pleskei
Morphology and classification
Classification: Passeriformes Locustellidae
Wing length: ♂ 70.0 ± 1.55mm (n = 253) ♀ 65.4 ± 1.38mm (135)
Tail length:♂ 63.5 ± 2.08mm (246)♀ 59.1 ± 1.9mm (118)
Culmen length: ♂ 19.5 ± 0.75mm (186)♀ 19.2 ± 0.67mm (109)
Tarsus length: ♂ 24.5 ± 0.65mm (251)♀ 23.9 ± 0.60mm (137)Weight:♂ 22.8 ± 1.38g (301)♀ 22.3 ± 2.30g (133)
Measurements from the population of Hakata Bay.

Appearance:
Styan's Grasshopper Warblers aresimilar in plumage color in males
and females. They are olive brownwith no reddish tinge on the upperpart and grayish white on theunderpart. The rectrices are rounded
and olive brown with the white tip Photo 1. Singing male of
Styan's Grasshopper Warexcept for a central pair of feathers.
blers [Hidehiko Kinoshita]
The ridge of the upper mandible isalmost black, while the lower mandible is beige. The commissure(gape) is yellowish in juveniles and some one year-olds, which
grow gradually darker to become olive in adults.

Vocalization:
Styan's Grasshopper Warblers have two types of songs. One is a
simple "Chichitt, chyr-chyr, chyr-chyr" and the other is with a trillof “shrrr”at the end of the song. Both have stereotypical song
structure but have individual variations in the length of syllables
and the way to add trills. They utter "Kirrrr" in a high-pitched trill
as an alarm call, when other birds intrude into their territory or
humans approach. This trill is also used as a contact call between
the sexes. They usually sing in a tree crown, but frequently sing inflight soon after arriving at the breeding grounds. Males also singfrequently during the night at the time females arrive at the breeding grounds.

Distribution and Habitat

advantage when attracting females (Nagata 1986). Mated males
sing less frequently until their partner begins to incubate eggs
because they guard their partner. When females start incubating,however, males begin to sing vigorously again because females
build a nest and incubate eggs by themselves. Both males andfemales feed the nestlings and fledglings. Though most females
breed once a season, some (4%) of the females that have fledged
the nestlings by June 15 lay the second clutch, leaving it to theirpartner to take care of the fledglings. Both males and females startmolting in July when they have finished breeding. However, thebirds that began to breed late start to molt the primaries while they
feed the young. Toward the end of the breeding period, males start
to leave the breeding grounds, leaving it to their partner to feed theyoung.

Nest:
They build a cup-shaped nest using
bamboo grass and dead leaves, andlay the veins of leaves and the fineroots of Ophiopogon japonicus in the
inner cup. They place these nests infine twigs and vines of Pseudosasa,
Eurya emarginata and vines at theheight from the base of Ophiopogonjaponicus near the ground to the Photo 2. Female delivering
food to the eight-day-old
canopy of Machilus thunbergii. The
young in a nest built onheight of the nest was 2.9m on averCelastrus orbiculatus.
age with a range of 0.3-7m in
Ohtsukuejima Islet. In Okitsujima Islet with a thicket ofPseudosasa, 65% of the nests were built on this plant. InOhtsukuejima Islet where Pseudosasa japonica is in short supply,
on the other hand, the nests were built in Euonymus japonicus,
Eurya emariginata, Litsea japonica, Machilus thunbergii as wellas Pseudosasa.

Egg:
The clutch size is 3.5 ± 0.6 eggs on average with a range of 2-5eggs (n = 109). The size of the egg is 19-21.5 mm by 14-15.1 mm.
The egg has brown flecks on a white or pale pink ground. Itweighs 1.8 g.

Distribution

Incubation and nestling periods and fledging success

Styan's Grasshopper Warblers breed in islands off the Korean
peninsula, Primorsky Province (Far East Russia), Kyushu(southern Japan), Shikoku, the Kii Peninsula (western Japan) andthe Izu Islands (central Japan). They winter from southern China to
the northern part of the Indo-China Peninsula.

The incubation period is about 13 days and the nestling period is
also about 13 days with a range of 12-15 days. The fledging success is more than 90% in Ohtsukuejima and Okitsujima Islets withno predators. Unhatched eggs and nest collapse due to bad weather
accounted for 5% and nearly 5% of the breeding failure, respectively. Fledglings are provided with food for 19 days on averagewith a range of 10-29 days, but this period is reduced in the latterpart of the breeding season.

Habitat:
They occur in a thicket of Sasa spp. (bamboo grass) and a field ofMiscanthus sinensis in Miyake Island of the Izu Islands, but in thelow laurel forests of islands off Kyushu and the Kii Peninsula.
Only several to several dozen Styan's Grasshopper Warblers occurin any of these islands except for Miyake and Chikuzenokinoshima Islands where several hundred birds are found because
the others are small islets. The population density is estimated tobe 10-25 pairs per ha in islets off the western coast of Kyushu, but
lower in their habitats from the Hyuga-nada (eastern area of Kyushu offshore) to the Kii Peninsula.

Life history
123wintering period

4567891011 12

breeding migration

Breeding system:
Styan's Grasshopper Warblers are basically a monogamous breeder, but some males (3.4%) breed polygynously (Nagata1988). Males with a large favorable territory are at an4Migration:
Styan's Grasshopper Warblers are summer visitors in Japan. Males
arrive at the breeding grounds from late April to mid-May. They
establish their territory and wait for females to arrive from May toearly June. In the latter part of the breeding season, most males
have departed from the breeding grounds by the end of August,and fledglings have also left the breeding grounds by early September.

Diet and foraging behavior
Styan's Grasshopper Warblers primarily feed to nestlings large soil
invertebrates, such as wood lice, beach fleas, centipedes and chilopods in the first half of the breeding period, but increasingly provide them with insects of lepidoptera, orthoptera, hymenoptera,etc. as the breeding period progresses, and also feed emerged cicadas to them at the end of the breeding period.

♪ http://www.bird-research.jp/1_shiryo/koe/uchiyama_090627_kashima_kuroda.mp3 ♪ http://www.bird-research.jp/1_shiryo/koe/uchiyama_c1_090627_kashima_kuroda.mp3
Haruo Kuroda

Haruo Kuroda

Bird Research News

Vol.5 No.52008.5.15.

© Japan Bird Research Association
Sumiyoshi 1-29-9, Fuchu, Tokyo, Japan● Strong site fidelity of males to the natal site and previous territories
In Hakata Bay, northern Kyushu, for instance, both males and females have a strong tendency to return to their natal island to breed.
Some females, however, settle down in the other islets of the bay(Nagata 1993). Once they have started breeding, both males andfemales show a strong site-fidelity and 57% of them return to theirprevious year's breeding grounds. Males have higher site-fidelityand tend to return to the same or neighboring breeding territory
every year. The rate of returning to the previous year's breeding site
is equivalent to the survival rate of this population. About 21% of
fledglings survive by the next year.

● Styan's Grasshopper Warblers and Middendorff's
Grasshopper Warblers (L. ochotensis)
The tail feathers are longer and thebill is thicker and longer in Styan's
Grasshopper Warblers than in Middendorff's Grasshopper Warblers. The
culmen length of Styan's GrasshopperWarblers exceeds 18mm. The ninthprimary is longer than the sixth one inMiddendorff's, while the sixth primary is longer than the ninth one in Styan's
GrasshopperWarblers(Williamson 1960, Yamashina 1941).
Styan's Grasshopper Warblers weretreated as a subspecies of Midden- Photo 3. Middendorff's
dorff's Grasshopper Warblers (theGrasshopper warbler (left)
Check-list of Japanese Birds the 5thand Styan's Grasshopper
edition), but now they are generallyWarbler (right) Dark andtreated as a separate species because
pale lateral bars of the tailfeathers are growth bars.
Nazarov & Shibaev (1983) advocated
They develop one band athat Styan's Grasshopper Warblers
day when molting.
should be a different species fromMiddendorff's Grasshopper Warblers
based on the morphological differences of Styan's Grasshopper Warblers breeding in the Bay of Peter the Great of Primorsky Province,
Far East Russia. Recent studies on the base sequence of the mitochondrial DNA have shown that Pallas's Grasshopper Warblers (L.
certhiola), Middendorff's Grasshopper Warblers and Styan's Grasshopper Warblers rapidly diverged into three different species in theeastern seaboard of the Eurasian Continent (Dovetski et al. 2004).
The differences of the mitochondrial base sequence suggest that
Styan's Grasshopper Warblers and Middendorff's Grasshopper Warblers diverged in the Riss glacial stage (about 140,000 years ago).
Recent study has also shown that there is so great a difference in thebase sequence of mitochondrial DNA between Styan's Grasshopper
Warblers and the populations of Ulleungdo Island, eastern Korea
and Primorsky Province, Far East Russia that they should be treatedas separate species. The phylogenetic relationship between Middendorff's Grasshopper Warblers and Styan's Grasshopper Warblers
requires reexamination in the future because Nazarov and Shibaev(1983) advocated that L. pleskei should be separate from L. ochotensis based on some characteristics of the population of Primorsky
Province.

● Tail feathers show a nutritional state
The lateral stripes of tail feathers are the growth bars that indicatesthe daily growth length of a feather when molting. The dark andpale stripes show daytime and nighttime growths, respectively. It ispossible, therefore, to estimate a nutritional state during the molting
period by measuring the width of a stripe. The tail growth bars werebroader in the males that survived into the next year than in the7males that did not survive, which6
meant that the survival rate was5higher in better-nourished males
4(Takaki et al. 2001). There is a3
positive correlation between the2width of the growth bar and the1
rs=0.894, p=0.002
number of fledglings per year
0(Fig. 1), which supports that
3.1
3.2
3.3
3.4
3.5
3.6
males with broader growth bars,
width of growth bars (mm)namely males which are better
Fig. 1. Relationship between thenourished after the breeding,width of growth bars and thearrive at the breeding grounds
number of fledglings. Males withand find their partner earlier
the broader growth bars have thebecause the early start of breedhigher breeding success.
ing increases the clutch size aswell as improves their chances of the second breeding.
Number of fledglings

Topics of ecology, behavior and conservation

バードリサーチ生態図鑑● Intrusion of rats (Rattus norvegicus) into a paradiseIn Ohtsukuejima Islet where Styan's Grasshopper Warblers used tohave a great breeding success, the nest predation of rats has increased in recent years. It is probably because the trees blown down
in recent typhoons and overgrown vines have allowed rats access tothe nests which they could not otherwise reach. There were 30 or 40
pairs of Styan's Grasshopper Warblers breeding in the 1980s, but thenumber of breeding pairs has decreased to less than 20 now in
Ohtuskuejima islet. Demographic stochasticity also raises the risk ofextinction, when the population decreases. Intruder rats (Rattusnorvegicus and R. rattus) have represented a threat to island birds asa nest predator.

Literature
Nagata H. 1986. Female choice in Middendorff's grasshopper-warbler. Auk
103:694-700.
Nagata H. 1988. An example of facultative polygyny in Middendorff's Grasshopper
Warbler. Ecol. Res. 3:57-60.
Nagata H. 1993. The structure of a local population and dispersal pattern in the
Styan's grasshopper warbler, Locustella pleskei. Ecol. Res. 8:1-9.
Nazarov Y.N. & Shibaev Y.V. 1983. On the breeding biology and taxonomic statusof Pleskei's Grasshopper Warbler, Locustella pleskei. (in Russian). Trudy Zool.
Inast. Akad. Nauk, USSR. 116:72-78.
Drovetski S.V., Zink R.M., Fadeev I.V., Nesterov E.V., Koblik E.A., Red’kin Y.A.
& Rohwer S. 2004. Mitochondrial phylogeny of Locustella and related genera. J.
Avian Biol. 35:105-110.
Takaki Y., Eguchi K. & Nagata H. 2001. The growth bars on tail feathers in themale Styan's Grasshopper Warbler may indicate quality. J. Avian Biol. 32:319325.
Williamson K. 1960. Identification for ringers 1. The genera Cettia, Locustella,Acrocephalus and Hippolais. British Trust for Ornithology.
Yamashina,Y. 1941. The birds of Japan and the ecology. Vol. 2. Iwanami Shoten.
[J]Authorfor Toki and Ecological Restoration,
Hisashi Nagata Center
Niigata University
I studied Styan's Grasshopper Warblers when I was in graduate school.
Although I miss those old days when I spent three or four days a week
in a tent on the uninhabited islets, I may be no longer strong enoughfor such fieldwork. I have also studied the avifauna of tropical forests
and the breeding ecology of JapaneseMarsh Warblers, Japanese Reed Buntings
and Great Reed Warblers along the Tonegawa river since I joined the staff of National Institute of Environmental Studies(NIES). I feel I must go back to the starting point and write up the unpublisheddata on Styan's Grasshopper Warblers in apaper.
hnagata@gs.niigata-u.ac.jp

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