Ornithol Sci 4: 173–177 (2005) SHORT COMMUNICATION Diet of the Japanese Night Heron Gorsachius goisagi in Japan Kazuto KAWAKAMI1,#, Hiroshi UCHIDA2 and Masaki FUJITA3 ORNITHOLOGICAL SCIENCE 1 Tama Forest Science Garden, Forestry and Forest Products Research Institute, Todori 1833, © The Ornithological Society Hachioji, Tokyo 193–0843, Japan of Japan 2005 2 Hiki Raptor Research Group, Matsuba 4–2–14, Higashimatsuyama, Saitama 355–0017, Japan 3 Laboratory of Biodiversity Science, School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1–1–1, Bunkyo-ku, Tokyo 113–8657, Japan The Japanese Night Heron Gorsachius goisagi, mains might be expected to be found if Japanese which breeds only in Japan, is a threatened species Night Herons consumed prey in proportion to their designated as Endangered by BirdLife International abundance on the forest floor. We therefore con- (2001). This species has decreased critically during ducted a simple feeding test to establish whether the latter half of twentieth century (Brazil 1991; Japanese Night Herons prefer or reject millipedes. Kawakami & Higuchi 2003). Despite the need for ur- In this paper, the dietary composition and prey gent conservation measures being recognized, a lack preferences of the Japanese Night Heron are de- of fundamental natural history information has pre- scribed, and its foraging microhabitats are discussed, vented us from adopting an effective conservation in the light of dietary preference. strategy for the Japanese Night Heron (Kushlan & Hafner 2000). Understanding the diet of a species is METHODS one very important aspect relevant to characterizing the ecological niche of such a rare and poorly known 1) Pellet Analysis bird. Pellets cast by Japanese Night Herons were col- The diet of the Japanese Night Heron has been re- lected every few days with the aid of mesh nets set ported to include earthworms, crustaceans, fish, and beneath four nests, one each in Hachioji City (from insects (Kawaguchi 1937; Yamashina 1941; Hyuga 15 July to 8 August 1999) and Akiruno City (from 16 1949; Tajima 1951; Hancock et al. 1978; Kiyosu to 28 June 2002) in Tokyo Metropolitan district, and 1978), however the primary food items reported have in Kodama Town (from 7 to 22 July 2000), Saitama differed between authors. For example, while Ya- Prefecture, and Hiroshima City (from 17 to 24 in July mashina (1941) and Kiyosu (1978) noted that earth- 2001), Hiroshima Prefecture. These four nests were worms and freshwater crabs were the main food located in broad-leaved deciduous forests or mixed items, Hancock et al. (1978) insisted that crustaceans, forest of conifer and deciduous trees consisting small fish, and insects comprised their main prey mainly of Quercus serrata, Zelkova serrata, Cryp- items. In order to remedy such inconsistency of di- tomeria japonica and Chamaechiparis obutusa. etary data, we collected pellets regurgitated by Japan- There were small streams near each of the nests ex- ese Night Herons to systematically analyse their di- cept that in Kodama City. The presence of chicks in etary composition. In addition to analysis of pellet each of the nests made it impossible to determine samples, we determined the dietary preferences of whether the pellets were ejected by adults or captive individuals in the hope that this would pro- nestlings. vide otherwise unavailable dietary data. During the We extracted fragmented animal remains from the course of inspecting pellet contents, we noticed a lack pellets, identified them and counted the minimum of millipede remains. Millipedes represent an abun- number of each species found in each pellet. dant element of the soil macrofauna, and their re- 2) Foraging preference (Received 22 March 2005; Accepted 28 July 2005) In order to confirm whether Japanese Night Herons # Corresponding author, E-mail: [email protected] prefer to forage on or avoid millipedes, we conducted 173 K. KAWAKAMI et al. Table 1. The species composition of prey found in the pellets of Japanese Night Herons. Numbers indicate the number of indi- viduals of each species. Numbers in brackets are percentages of each species. Order Survey place Family Species Hachioji Akiruno Saitama Hiroshima Snails Architaenioglossa Cyclophoridae Cyclotus campanulatus 5 (38) 8 (40) Discopoda Pleuroceridae Semisulcospira libertina 4 (7) Stylommatophora Bradybaenidae Aegista proba goniosoma 1 (1) Clausiliidae Phaedusa japonica 10 (12) 6 (11) Zaptychopsis buschii 11 (15) Clausiliidae sp. 2 (3) Camaenidae Satsuma japonica 4 (7) Subtotal 24 (29) 14 (26) 5 (38) 8 (40) Spiders Araneae Araneae sp. 5 (6) Subtotal 5 (6) 0 (0) 0 (0) 0 (0) Crabs Decapoda Potamidae Geothelphusa dehaani 4 (5) 31 (57) 8 (40) Subtotal 4 (5) 31 (57) 0 (0) 8 (40) Insects Hemiptera Cicadidae Cicadidae sp. (imago) 2 (2) 1 (8) Lepidoptera Lepidoptera sp. (larva) 2 (15) Coleoptera Carabidae Carabus sp. (imago) 14 (17) Carabus sp. (larva) 17 (20) Pterostichus sp. (imago) 1 (1) Carabidae sp. (imago) 5 (6) 2 (4) Scarabaeidae Melolonta sp.(imago) 1 (2) Heptophylla picea (imago) 3 (4) Mimela costata (imago) 1 (1) Mimela sp. (imago) 1 (1) Anomala albopilosa albopilosa (imago) 1 (1) 174 Diet of the Japanese Night Heron Table 1. (Continued). Order Survey place Family Species Hachioji Akiruno Saitama Hiroshima Anomala sp. (imago) 1 (1) Elateridae Elateridae sp. (imago) 1 (5) Elateridae sp. (larva) 1 (1) 1 (2) Coccinellidae Coccinellidae sp. (larva) 1 (1) Coleoptera sp. (imago) 3 (4) 3 (6) 1 (8) Coleoptera sp. (larva) 2 (15) 2 (10) Insects sp. (imago) 2 (4) 2 (15) 1 (5) Subtotal 51 (61) 9 (17) 8 (62) 4 (20) Total 84 54 13 20 Number of pellets 31 35 18 8 an experiment during December 2004 using a captive exactly from the small pieces of exoskeleton rem- individual, a young bird rescued two months before nants in the pellets, it is reasonable to assume that the experiment. Ten millipedes Fusiulus takakuwai, they were Carabus granulatus esakianus, the domi- earthworms Eisenia fetida and mealworms Tenebrio nant species there. molitor (about 30, 100 and 25 mm in total length, re- spectively) were placed together on a plastic vessel 2) Foraging preference (25 cmϫ35 cm) in the cage of the captive night During the five replications of the feeding experi- heron. One hour after these food items had been pre- ment all of the earthworms and mealworms provided sented to the heron, the numbers of each species left were eaten, whereas none of the millipedes were con- on the vessel were counted. This experiment was re- sumed, though some were pecked at and torn apart. peated five times. DISCUSSION RESULTS Land snails, freshwater crabs, ground, and scarabid 1) Pellet analysis beetles were the major prey items found in the pellets The undigested remains of snails, crabs, insects, of Japanese Night Herons, whereas no fish were de- and spiders were found in the pellets collected from tected. The land snails found in pellets at all the sur- the four survey sites (Table 1). Of 171 prey items vey sites were typical terrestrial species found on the identified to the lowest possible taxon, snails ac- forest floor, with the exception of S. libertina, which counted for 26–40% in numbers, of which species in occurs in freshwater (Taiji Kurozumi, personal com- the families Clausiliidae and Cyclophoridae predomi- munication). The Clausiliidae species are common in nated. With the exception of the remains of four the survey areas and are frequently found near fallen Semisulcospira libertina, nearly 90% of all snails de- trees. As most snails found in the pellets were adult tected were adult land snails. individuals, there is the possibility that Japanese All the crustaceans found were identified as the Night Herons forage selectively on large individuals. Japanese Freshwater Crabs Geothelphusa dehaani, But, as the softer and weaker shells of immature and these accounted for 0–57% of the food items in snails might be prone to being fully digested, this ap- number. Most of the insect remains were those of parent preference for larger animals should be further beetles, such as ground beetles and scarab beetles. tested. Japanese Freshwater Crabs were found at Carabus sp. was apparently especially frequent at three of the survey sites and were particularly com- Hachioji. While the species could not be identified mon at two of the study sites. They occur not only in 175 K. KAWAKAMI et al. freshwater courses, but also in terrestrial habitats near certain that Japanese Night Herons frequently forage streams. The Carabidae species found frequently in on earthworms from various past reports (i.e. Ya- the heron’s pellets, are inhabitants of the forest floor. mashina 1941; Kiyosu 1978). In fact Japanese Night Though most of the Scarabaeidae species found in Herons have often been observed to catch and eat the pellets are herbivores that eat plant leaves, they earthworms (Kazuto Kawakami unpublished), and are also often found on the ground (Masahiro Orobdella sp. (Kazuto Kawakami unpublished). Nagano, personal communication). There is also the possibility that night herons eat These results of pellet analysis indicate that Japan- Hirudinoidea species, however, they are also very dif- ese Night Herons mainly forage on soil animals on ficult to detect by pellet analysis. the forest floor. At the same time, it appears that the Japanese Night Herons have somewhat shorter and night herons prefer wet or damp ground, sometimes thicker beaks than other herons (Yamashina 1941; near streams, as foraging habitat, where they can de- Kawakami 2002), while herons in general have long tect land snails and freshwater crabs. Japanese Night bills (del Hoyo 1992), which are suitable for preying Herons have previously been reported to forage and on aquatic animals. Their morphology is considered breed near streams by Yamashina (1941), Hyuga to be adapted for foraging on soil animals by digging, (1949) and Uchida (1996), and our dietary data sup- as they have often been seen digging for earthworms port these previous observations.