Ornithol Sci 4: 73–79 (2005)

ORIGINAL ARTICLE The distribution of the Malayan Night melanolophus in the Yaeyama and Miyako Islands, southern

Kazuto KAWAKAMI1,# and Masaki FUJITA2

1 Tama Forest Science Garden, Forestry and Forest Products Research Institute, Todori 1833, Hachioji, Tokyo 193–0843, Japan 2 Laboratory of Biodiversity Science, School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1–1–1, Bunkyo-ku, Tokyo 113–8657, Japan

Abstract The Malayan Gorsachius melanolophus is a threatened ORNITHOLOGICAL species that inhabits the Yaeyama Island group in the extreme southwest of the SCIENCE Ryukyu Archipelago, southern Japan. The species’ distribution in Japan, which has © The Ornithological Society been poorly known, was surveyed on the basis of sound and sight records, and inter- of Japan 2005 views. The species was confirmed to occur on Ishigaki, Iriomote, Kuroshima, Ko- hama, Taketomi, , Yonaguni, Miyako, Kurima, and Tarama islands. This range is wider than expected and records were independent of the area of islands. The past underestimation of the species’ range was likely to have been the result of a lack of research effort and the unremarkable ecology and morphology of the species. The population density was found to be higher on Iriomote Is., covered with abundant for- est, than on Ishigaki Is. with more degraded forests. Despite the wider than previously thought range, its range is still not very extensive in Japan; furthermore, increasing predators and introduced competitors may well endanger the population in the near future.

Key words Distribution, Gorsachius melanolophus, Malayan Night Heron, Popula- tion density, The

The Malayan Night Heron Gorsachius melanolo- Archipelago (Fig. 1, The Ornithological Society of phus ranges from and to Southeast Japan 2000). Though it has been observed on Miyako , Southern , , , , and Aguni islands, it was considered a winter visitor , Philippine and Japan (del Hoyo et al. there (Kugai & Yamamoto 1981; Brazil 1991), how- 1992; Ornithological Society of Japan 2000). This ever, this distribution pattern seems to be unnatural, species prefers tropical and subtropical wet forests as because there are many other islands in the immedi- its breeding habitats (Hancock et al. 1978; del Hoyo ate vicinity. The Malayan Night Heron had even been et al. 1992). While it is a migratory in some observed in Tokushima Prefecture in 1984 and on areas (Hancock et al. 1978), it is resident in Japan Rishiri Island of the northwest coast of Hokkaido (Ornithological Society of Japan 2000). This heron is Prefecture in 2000 (Yoshida 1986; Kosugi et al. classified as a vulnerable species in the Japanese Red 2005), indicating that this species has the ability to Data Book (Ministry of the Environment 2002). disperse to other islands. There have, however, been few studies of its ecology The Malayan Night Heron is an unimposing and distribution, though such information is essential species because they prefer dense humid forests, do for its conservation (Kushlan & Hafner 2000). not move actively, seldom fly, do not have bright In Japan, this species has been reported to breed plumage, and call only before sunrise and after sunset only on Ishigaki, Iriomote and Kuroshima islands in (Hancock et al. 1978; Kabaya & Matsuda 2001). the Yaeyama island group, of the southern Ryukyu There was, therefore, the possibility that they might inhabit islands near Ishigaki, Iriomote and Kuroshima (Received 26 July 2004; Accepted 28 October 2004) islands, but had not yet been identified there. Thus, # Corresponding author, E-mail: [email protected] we investigated their distribution throughout the

73 K. KAWAKAMI and M. FUJITA

Fig. 1. Location of the islands in the study area.

Yaeyama and Miyako Islands. We also surveyed the a speed of 4 km/hour. The survey was conducted in population density of this species to assess their re- lowland forests in Kuroshima Is. (26°15N, 124° cent status. 01E, 10.02 km2), Kohama Is. (24°20N, 123°59E, It is difficult to investigate the species visually be- 7.84 km2), Taketomi Is. (24°19N, 124°05E, 5.42 cause of the reasons stated earlier. We therefore used km2), Hateruma Is. (24°03N, 123°47E, 12.77 km2) their calls to detect them. The species calls in the and Yonaguni Is. (24°27N, 123°00E, 28.84 km2) in early breeding season, mainly in March, before nest the Yaeyama Islands, and on Miyako Is. (24°47N, building (K. Kawakami, unpublished). Thus, we were 125°20E, 159.05 km2), Irabu Is. (24°50N, 125° able to confirm their presence by surveying their call- 11E, 29.05 km2), Ikema Is. (24°56N, 125°25E, ing activity. In this study we first checked when they 2.83 km2), Kurima Is. (24°43N, 125°15E, 2.84 km2) called most frequently. Then, their distribution was and Tarama Is. (24°39N, 124°42E, 19.73 km2) in investigated on ten islands in the Yaeyama and the Miyako Islands from 8 to 21 March 2003 and Miyako island groups. Finally, the population densi- from 13 to 21 March 2004 (see Fig. 2). On Ikema and ties on Ishigaki and Iriomote islands, were analyzed Kurima islands, surveys were conducted without to assess their abundance there. walking, because the forests there were small enough for all calls to be heard from one point (see Fig. 2). METHODS In addition, we checked for visually during the daytime on every island in March 2003, and on 1) Calling activity Kuroshima, Kohama, and Taketomi islands from In order to establish a research schedule, we 13–15 December 2003 during a non-breeding season checked when the species calls most frequently. survey. Interviews were also conducted with local Thus, surveys of seven individuals were conducted people on Kuroshima, Kohama, Taketomi, Hateruma, overnight from 1800 to 0730 on Ishigaki Is. (3 birds), Yonaguni, Miyako, Irabu and Tarama islands, in Iriomote Is. (2 birds) and Kohama Is. (2 birds) on order to supplement the distribution data. 15–17 March 2004. Their calling frequency was recorded every ten minutes. 3) Population density and size One phrase of their ‘call’ consists of repeated short In order to assess the abundance of Malayan Night syllables that sound like “pooh” (Kabaya & Matsuda , we mapped the calling locations in montane 2001). We counted one phrase as one ‘call’, and forests in the Mt. Ban-na area and riparian forests recorded the number of phrases per ten minutes. The along the Miyara River of Ishigaki Is. in March 2002 calls could be heard from more than 500 m away in and in montane forests in the Ohtomi area of Iriomote calm weather. Is. in March 2003. With this data, nearest neighbor distances were calculated for each individual giving 2) Distribution an index of population density. These values were According to the above survey, the Malayan Night then compared both between islands and between dif- Heron calls most frequently between 1840–1930 ferent habitats on Ishigaki Is. using the Mann–Whit- in the evening and 0600–0630 in the morning in ney U-test. Since female Japanese Night Herons G. March. During these time periods, we recorded the goisagi, a closely related congener of the Malayan location of the calling birds on maps while walking at Night Heron, sometimes call like males (H. Uchida &

74 The distribution of the Malayan Night Heron

Fig. 2. The survey routes and the locations where Malayan Night Herons were recorded. Thin black lines: sur- vey routes; black triangles: survey points; white circles: calling points in 2003; black circles: calling points in 2004; hatch marks: locations where individuals were observed in March 2003; gray circles: locations where indi- viduals were observed in December 2003.

K. Kawakami, unpublished), there is the possibility population density by the area. that female Malayan Night Herons also call like males. Therefore, we excluded data within an area of RESULTS less than 100 meters in order to avoid overestimation. However, as the frequency of calling females among 1) Calling activity Japanese Night Herons is very low, it is assumedly All individuals frequently called from 1840 to the same with Malayan Night Herons. 1930 and from 0600 to 0630 (Fig. 3). They rarely Next, we estimated the population size on the two called during other time periods. islands. Firstly, the population densities were calcu- lated on the assumption that the territories of the 2) Distribution species are in a honeycomb pattern. In this calcula- Calls of Malayan Night Herons were recorded on tion, the mean distance obtained with the above Kuroshima, Kohama, Taketomi, Hateruma, Yona- method was applied as the distance between centers guni, Miyako, and Tarama islands in both 2003 and of neighboring territories. Given that the areas of for- 2004 (Table 1, Fig. 2), and on Kohama, Hateruma est habitats are about 80 km2 on Ishigaki Is. and about and Kurima islands only in 2004. Individual adults 250 km2 on Iriomote Is. (The Ministry of Agriculture, were observed on Kuroshima, Kohama, and Miyako Forestry and Fisheries of Japan, unpublished), popu- islands during the survey period in 2003. lation sizes were calculated simply by multiplying the During the non-breeding season, some adults were

75 K. KAWAKAMI and M. FUJITA

Fig. 3. Calling frequency of Malayan Night Herons (From upper: 3birds on Ishigaki Is., 2birds on Iriomote Is, and 2birds on Kohama Is.) recorded at 10 minutes intervals on 15–17 March 2004. The frequency was counted as the number of phrases during ten minute periods. Sunset was at 1853–1854 and sunrise was at 0650–0652 on the survey days. also observed on Kuroshima, Kohama, and Taketomi forests of Iriomote Is., 20 individuals were located islands (Table 1). and no data were excluded. Local information indicated that Malayan Night Nearest-neighbor distances averaged 27222 m Herons had been observed for at least 10 years on (meanSE, n23) in montane forest on Ishigaki, Kohama, Kuroshima, and Miyako islands (Table 1). 31621 m (meanSE, n25) in riparian forest on Ishigaki, and 2108m (meanSE, n20) in mon- 3) Population density and size tane forest on Iriomote Is.. While there was no signif- In the montane and riparian forests of Ishigaki Is., icant difference between the two habitats on Ishigaki 25 calling birds were located in each habitat. But two Is. (Mann-Whitney U209.5, z1.62, P0.1053), individuals of the former were excluded from the fol- the nearest-neighbor distance was significantly lowing analysis, because they were less than 100 me- shorter on Iriomote Is. (Fig. 4; Mann–Whitney ters from their nearest neighbors. In the montane U137, z2.264, P0.05).

76 The distribution of the Malayan Night Heron

Table 1. Detection of Malayan Night Herons by song censuses, observations and interviews at each island. : detected, : un- detected, : unsurveyed.

Song censuses Observations Interviews Mar 2003 Mar 2004 Mar 2003 Dec 2003

Kuroshima Is Kohama Is Taketomi Is Hateruma Is – Yonaguni Is – Miyako Is – Irabu Is – Ikema Is –– Kurima Is –– Tarama Is –

Table 2.

Date of survey

2003 2004

Kuroshima Is 8–9 21 Mar 16–17 Mar Kohama Is 8–9 Mar 16–17 Mar Taketomi Is 8–9 Mar 15–16 Mar Hateruma Is 11–12 Mar 17–18 Mar Yonaguni Is 11–12 Mar 13–15 Mar Miyako Is 13–14 Mar 19–20 Mar Irabu Is 14–15 Mar 20–21 Mar Ikema Is – 20– Mar Kurima Is 15– Mar 20– Mar Tarama Is 13–14 Mar 19–21 Mar

The population densities, calculated using the above values, were 26.5 per km2 on Ishigaki Is. and 52.4 per km2 on Iriomote Is. The mean distance be- tween nearest neighbors in both montane and riparian Fig. 4. The mean nearest neighbor distance in riparian forests and montane forests on Ishigaki Is. and in montane habitats on Ishigaki Is. was 295 m. The total number forests on Iriomote Is. Bars represent SE. The numbers above of individuals was estimated to be about 2,000 on the bars show the sample size of each habitat. Ishigaki Is. and about 13,000 on Iriomote Is. nonetheless have been there. Their existence is sug- DISCUSSION gested by the fact that individuals were observed both during the breeding and non-breeding seasons in 1) Distribution in the Yaeyama Islands 2003 and information was provided of regular obser- On Kuroshima, Kohama, and Taketomi islands, vations on Kuroshima Is. and Kohama Is. These find- many calls of Malayan Night Herons were recorded ings suggest that this species continuously inhabits in March 2004, while few calls were heard there in these islands. March 2003. Since strong winds were blowing on the Though Yonaguni Is. is situated between Taiwan survey days in 2003, wind may have inhibited the and Iriomote Is., two of the main range areas of the vocal activity of this species. Thus, while their calls species, and though Yonaguni has sufficient large were not heard during the survey periods, birds may forests for breeding, we were able to detect very few

77 K. KAWAKAMI and M. FUJITA calls there. This island may be too far away from the While the population densities did not differ be- main population to receive individuals from other is- tween montane and riparian habitats, the density on lands frequently. There is also the possibility that spe- Ishigaki Is. was significantly lower than that on Iri- cial ecological factors exist. For instance, the Yona- omote Is. Iriomote Is. has larger forests and its breed- guni keeled ratsnake Elaphe carinata yonaguniensis, ing habitats have been less disturbed by economic de- which occurs only on Yonaguni Is., may be an effec- velopment than on Ishigaki Is., which might explain tive predator of the eggs of Malayan Night Herons. In the difference in population densities. The population contrast, Hateruma Is. has very small forests, thus it densities of the two islands are considered to be high was reasonable that only a few calls were recorded enough to be sustainable at the present time, as they there. indicate that there are several thousands of Malayan Night Herons on both islands. There is, however, the 2) Distribution in the Miyako Islands possibility that the total number of individuals has The Malayan Night Heron has been reported as been overestimated. The calculations were based on being observed every year on Miyako Is. (Sunagawa the assumption that birds fully occupy their forest 2001), and our results (i.e. call detection and inter- habitats, and this may not reflect the actual situation. views) are consistent with that. Sunagawa (2001) It is necessary, therefore, for future research to inves- mentioned that the species might breed on the island. tigate their habitat preferences in detail. We recorded calls of the species, which are consid- The species was found to inhabit islands independ- ered to be part of breeding behaviour. While it is nat- ently of their size. It was found that Malayan Night ural to assume that Malayan Night Herons breed on Herons inhabit all of the Yaeyama Islands surveyed, Miyako Is., the area of forests as breeding habitat is and three of the Miyako Islands, though some of the very small there, and it may not be enough to sustain populations may be temporary. As Malayan Night an independent population. So, perhaps some individ- Herons are migratory in Southeast Asia, it seems very uals may come from the Yaeyama population. likely that they have the ability to move between is- On Tarama Is., calls were heard both in 2003 and lands. It is therefore natural that populations of Ishi- 2004, though the forest area is not so large. This pop- gaki Is. and Iriomote Is. help sustain populations on ulation is also likely maintained with arrivals from other islands nearby through occasional dispersal to the Yaeyama population. Records show that this them. Malayan Night Herons were not previously species was observed on the island in October 2003 considered to inhabit many of these islands, simply (S. Seki pers. comm.), suggesting that at least some because of a lack of information and perhaps because individuals have occurred there in the past few years. they were over-looked, given their unremarkable eco- Adults of this species tend to use the same area for logical and morphological characters; or, conversely, breeding, and sometimes even the same trees for they may have extended their range. nesting, every year (C. Otani pers. comm.; S. Shi- Though it was found that they occurred on more is- ratama pers. comm.). They may possibly breed on lands than previously thought, their range is still not Tarama Is. very large in Japan. Recently Jungle Crows Corvus Except for one call heard on Kurima Is., there were macrorhynchos, which have apparently increased in no records from other islands, so the likelihood of number on Ishigaki Is., have been observed to prey breeding is not very high there. upon the eggs of Malayan Night Herons (Kawakami 2002). In addition, introduced Indian Peafowls Pavo 3) The status of the population cristatus have become feral and are increasing in As calling is part of the initial phase of this number on Ishigaki, Iriomote, Kuroshima, Kohama, species’ breeding behaviour, there is the possibility Yonaguni, Miyako, and Irabu islands (Tanaka & that they breed on the islands where many calls were Takehara 2003). Because Indian Peafowl also forages recorded. As the closely related Japanese Night upon epigeal on the ground (Long 1981; del Heron frequently calls immediately before nest build- Hoyo et al. 1994), it is a potential new competitor for ing (K. Kawakami & H. Uchida, unpublished), it is the Malayan Night Heron in Japan. There has been quite possible that Malayan Night Herons have the little assessment of the status of the Malayan Night same habits. Thus, Miyako Is., Tarama Is. and most Heron in Japan because of a lack of information and islands of the Yaeyama group may have maintained concern. It is therefore necessary to study their ecol- breeding populations, at least in 2003 and 2004. ogy and monitor changes in their population densities

78 The distribution of the Malayan Night Heron and distribution in order to conserve them. Japanese Night Heron. Wild bird 67(6): 13–15 (in Japanese). ACKNOWLEDGMENTS Kosugi K, Tamaki K & Sato M (2005) Rare visits and newly recorded birds from Rishiri Island, Northern We wish to thank Minako Murakami, Ryoko Kanzawa, Hokkaido (3). Rishiri Studies 24: 5–9 (in Japanese). Nanami Kawamura, Ako Sukegawa, Takehiro Fujiwara and Kugai K & Yamamoto A (1981) Bird List of Miyako Is- Yoko Hashiguchi for their field assistance, Seiki Shiratama, land. Okinawa Asso Educ 14: 15–29. Yoichiro Sakiyama, Chikara Otani, Shin-Ichi Seki, Kazuki Kushlan JA & Hafner H (2000) Heron Conservation. Sugiyama and Ken-Ichi Iseki for providing important informa- Academic Press, London. tion and Dr. Isao Nishiumi, two anonymous referees and Dr. Mark Brazil for their helpful comments and improvement of Long JL (1981) Introduced Birds of the World. Reed, our English. Wellington. Ministry of the Environment (2002) Threatened wildlife REFERENCES of Japan—Red Data Book 2nd ed. Vol. 2 Aves. Japan Wildlife Research Center, Tokyo (in Japanese). Brazil M (1991) The Birds of Japan. Christopher Helm Ornithological Society of Japan (2000) Check-list of Ltd, London. Japanese Birds. Sixth Revised Edition. Ornithologi- del Hoyo J, Elliott A & Sargatal J (1992) Handbook of cal Society of Japan, Obihiro. the Birds of the World. Vol. 1. Lynx Edicions, Sunagawa E (2001) Birds of the Miyako Islands. Ni- Barcelona. raisha, Naha (in Japanese). Hancock J, Elliott H & Gilmer R (1978) The Herons of Tanaka S & Takehara K (2003) Distribution and present the World. Harper & Row Pub Inc, New York. status of feral Common Peafowls Pavo cristatus in the Kabaya T & Matsuda M (2001) The Songs and Calls of , the . Bull Okinawa 420 Birds in Japan. Shogakukan Inc, Tokyo (in Pref Mus 29: 19–24 (in Japanese). Japanese). Yoshida K (1986) A record of Malayan Night Heron in Kawakami K (2002) The possibility of extinction on Tokushima Prefecture. Tori 35: 37 (in Japanese).

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