BirdLife species factsheet for Japanese Night-heron
Japanese Night-heron has a breeding range that extends throughout Japan, including the islands of Honshu, Kyushu, and Shikoku (Fujimaki, 2012). It is also a rare vagrant in Hokkaido but lacks any breeding records here. Breeding has additionally been recorded from Chinese Taiwan, South Korea, and mainland China, albeit in small numbers (Oh et al. 2010; He et al. 2016). The species is also a passage migrant in Russia, coastal China, Hong Kong (China), and Chinese Taiwan. Main wintering areas are in the Philippines, although records have also shown its presence as a non-breeding visitor in Indonesia, Brunei and Palau (Martinez-Vilalta et al. 2020). The species prefers high elevations, often recorded between 1,500-2,400m, and breeds commonly in suburban forest patches, as well as rivers and swamps of thicker forests (Martinez-Vilalta et al. 2020).
The species was considered to have undergone rapid declines due to deforestation and habitat conversion in the past (Martinez-Vilalta et al. 2020). However, recent forest analyses suggest that forest loss within the range of the Japanese Night-heron has reduced (Tracewski et al. 2016; Global Forest Watch, 2020), estimated at 2.99% decline, rounded here to a 3% decline over a 3-generation period (16.5 years; Bird et al. 2020)*. The species is however marginally threatened by additional factors such as hunting, introduced taxa, and predation (Martinez-Vilalta et al. 2020). Currently, the number of individuals is thought to estimate 11,250-15,000 individuals; this is based on mating call detection studies in rural secondary forests of central Japan and an estimated population density of 23 individuals per 100 km2 (over a total range of rural secondary forests of c. 72,000 km2) (Hamaguchi et al. 2014, Watanabe et al. 2012). The number of mature individuals is estimated to be 8,280; however, to account for difficulty in monitoring due to the inconspicuousness of the species, population size is tentatively placed here in the band of 7,500-9,999 mature individuals.
The Japanese Night-heron is currently listed as Endangered under Criteria C2a(i), based on a declining and restricted population size, as well as fewer than 250 mature individuals in each existing subpopulation. However, information regarding new population estimates and range may warrant a change in Red List status. Therefore, the species will be re-assessed against all criteria:
Criterion A – The population trend of this species has not been formerly quantified. However, recent forest loss estimates show a negligible decline, approximately 3% over 16.5 years (3 generations)* (Tracewski et al. 2016; Global Forest Watch, 2020). Current forest loss is suspected to have maintained this slowed rate, at a likely pace of ≤3% decline over a 3-generation period. The species may however be affected by other marginal factors, albeit, in the absence of recent information detailing the exact effects, an appropriate rate of decline cannot be quantified. Thus, the best available information on forest loss rates can be used to infer a population size reduction under Criterion A. However, the species does not meet or approach the required thresholds for a threatened status. Therefore, the species qualifies as Least Concern under Criterion A.
Criterion B – The Extent of Occurrence (EOO) of this species is estimated to be 631,000 km2. This is above the threshold for a threatened status under Criterion B1. The Area of Occupancy (AOO) has not been quantified as required (IUCN Standards and Petitions Committee 2019), so the species cannot be assessed under Criterion B2. Therefore, the Japanese Night-heron qualifies as Least Concern under Criterion B1.
Criterion C – The number of mature individuals is thought to be approximately 7,500-9,999. This initially meets the required thresholds for a Vulnerable status. Based on the slow rate of decline however (approximately ≤3% over a 3-generation period), the species does not exceed the threshold for listing under Subcriterion C1. The current rate of decline may however be used to infer a continued decline under Subcriterion C2. As per the Waterbird Population Estimates, the species is thought to occur in only one flyaway population across Eastern and South-eastern Asia (Wetlands International, 2020). Under assumption that this is equivalent to one subpopulation only, it is therefore likely that all mature individuals occur here. As such, under a suspected decline, the species approaches the relevant threshold for sub-criterion a(ii). The species therefore qualifies as Near Threatened under Criterion C2a(ii).
Criterion D – The number of mature individuals for this species is above the required thresholds for a threatened status under this criterion. Therefore, it qualifies Least Concern under Criterion D.
Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.
Therefore, it is suggested that the Japanese Night-heron (Gorsachius goisagi) be reclassified as Near Threatened C2a(ii). The species was previously considered to have undergone population declines as a result of heavy deforestation and habitat loss. This is thought to have primarily occurred since the 1960’s (Kawakami and Higuchi, 2003). The species then saw uplisting from Vulnerable to Endangered in the 1988-1994 period, following continued decline in the 1980’s and early 1990’s with a subsequent drop in population size to below 1,000 mature individuals (C. Green in litt. 2020). The species is also currently listed as Vulnerable under Japan’s Ministry of the Environment Red List (2020). However, deforestation is thought to have slowed in decline across the species’s 3-generation period (16.5 years), with forest loss estimates recorded for the period between 2001 and 2018 (Tracewski et al. 2016; Global Forest Watch, 2020). The population of the species could therefore have similarly seen slower rates of decline prior to 2016-2020, and possibly as early as 1996-2000 or 2000-2004. Therefore, we welcome any comments on the above proposed listing, and specifically ask for information regarding the timeframe of the possibility in a genuine status improvement of the Japanese Night-heron.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. By submitting a comment, you confirm that you agree to the Comment Policy.
*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).
An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.
Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. 2020. Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.
C, Green. (2020). Heron Specialist Group. In litt.
Fujimaki, Y. 2012. The birds of Hokkaido 4th ed. Kyokuto Chorui Kenkyukai, Hokkaido.
Global Forest Watch. 2020. Interactive Forest Change Mapping Tool. http://www.globalforestwatch.org (Accessed 21st May 2020).
Hamaguchi, H., Ishikawa M., Konishi, K., Nagai, T., Oshika, H. and Kawakami, K. 2014. A habitat model for the Japanese night heron in the West mikawa area of Aichi prefecture, Japan. Japan. Jpn J Ornithol 63: 33–41.
He, F., Wen, C., Lin, J., Jiang, H., Lin, Z. and Xiao, H. 2016. A brief on the current occurrence of Gorsachius spp. in mainland China. Zoological Systematics 41(3): 315–317.
Hongshik Oh; Youngho Kim; Namkyu Kim. 2010. First breeding record of Japanese Night Heron Gorsachius gorsagi in Korea. Ornithological Science 9: 131-134.
IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf
Kawakami, K.; Higuchi, H. 2003. Population trend estimation of three threatened bird species in Japanese rural forests: the Japanese Night. Heron Gorsachius goisagi, Goshawk Accipiter gentilis and Grey-faced Buzzard Butastur indicus. Journal of Yamashina Institute for Ornithology; 35:19-29.
Martinez-Vilalta, A., Motis, A., and Kirwan, G. M. (2020). Japanese Night-heron (Gorsachius goisagi), version 1.0. In Birds of the World (del Hoyo, J., Elliott, A., Sargatal, J., Christie, D. A., and de Juana, E., Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.janher1.01
Ministry of the Environment Red List (2020). Attachment 3; http://www.env.go.jp/press/107905.html; Accessed 25th May 2020.
Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.
Watanabe, T.; Okuyama, M.; Fukamachi, K. 2012. A review of Japan’s environmental policies for Satoyama and Satoumi landscape restoration. Global Environmental Research 16: 125-135.
Wetlands International (2020). Waterbird Population Estimates. wpe.wetlands.org; Accessed 25th May 2020.