Justification of Red List category
This species has been downlisted in status due to a larger population size than previously considered. However based on ongoing deforestation across breeding areas and trapping pressures across wintering grounds, the population is inferred to be undergoing a continued decline. Thus, the species now qualifies for listing as Vulnerable.
Previous work in Japan suggests the assertion that the global population comprises fewer than 1,000 individuals may have been overly pessimistic. These estimations are however not considered accurate by some researchers (K. Kawakami in litt. 2016). Recent mating call detections however recorded 23 individuals per 100 km2 in rural secondary forests across the Aichi Prefecture in central Japan (Hamaguchi et al. 2014). The total area of rural secondary forests in Honshu, Kyushu and Shikoku islands estimates to 72,000 km2 (Watanabe et al. 2012). Thus, the number of mature individuals is thought to be approximately 8,280. However, mating call detection studies have been considered as an unreliable method of monitoring breeding numbers in this instance due to the species's inconspicuous habits and the potential of receiving duplicated records (K. Ohata in litt. 2020). Similar calling surveys have for example not recorded any nests, and as such breeding birds, despite observing other calling individuals. It is also likely that surveys specific to limited sites (the Aichi area in this instance), may not yield results that are compatible with other suitable habitats across the species's range (K. Ohata in litt. 2020). Habitat models have additionally been considered impractical methods of estimating population numbers or trends (J. Kushlan in litt. 2020). Hence, to account for any uncertainty, the true figure is placed here in the band of 5,000-9,999 mature individuals, roughly equating to 7,500-15,000 individuals. As per the Waterbird Population Estimates, the species is also thought to occur in only one flyaway population across Eastern and South-eastern Asia (Wetlands International 2020). This is assumed to represent one subpopulation holding all mature individuals.
The species had previously considered to have undergone rapid declines due to deforestation and habitat conversion (Martinez-Vilalta et al. 2020). However, recent forest loss estimates show a negligible decline (Tracewski et al. 2016, Global Forest Watch 2020), equating to 3% over three generations (16.5 years; Bird et al. 2020). Forest destruction is also considered to no longer be a threat across breeding sites in Japan (S. Chan in litt. 2020). However, the population is thought to be rapidly declining at migratory and wintering grounds (S. Chan in litt. 2020), primarily owed to hunting pressure. Breeding areas may also suffer from problematic native and non-native species, as well as some level of continued habitat degradation. Thus, the population is inferred to be undergoing a continued decline of 1-9% over three generations.
Gorsachius goisagi breeds in Japan. Breeding has been mainly recorded from Honshu, Kyushu and Shikoku islands, while there are relatively few records in northern Honshu (Wild Bird Society of Japan [Tokyo] in litt. 2020). During 2009-2010, 26 nests were found in West Mikawa in the Aichi Prefecture (Ishikawa et al. 2012). In addition to confirmed breeding sites, it is possible that there may be 15 additional sites in Japan (Kushlan and Hancock 2005). It is rare vagrant in Hokkaido with no breeding record there (Fujimaki 2012). There has been one report of breeding from Taiwan, China, and recent work has discovered a breeding site at Jeju Island, South Korea (Oh et al. 2010). It has also been recorded in spring and summer in Russia (Primorye and Sakhalin), and is a passage migrant in coastal mainland China (where one individual was recently seen in the Xiamen City harbour of Southeastern Fujian; He Fenqi in litt. 2020), Hong Kong, and Taiwan (China). There may also be a small resident flock occurring during the breeding seasons in the Jiangxi region of mainland China (He et al. 2016). The main wintering area appears to be in the Philippines, but it has also been recorded as a non-breeding visitor to Indonesia, and as a vagrant to Brunei and Palau. Improved awareness of the identification criteria for immatures of this species has led to a marked increase in records from the Philippines (D. Allen in litt. 2012). It was apparently locally common in Japan until the 1970s, but by the 1980s and 1990s had disappeared from many of its former breeding sites. Recent survey work in Japan and increasing numbers of records from the Philippines imply that the population is larger than previously assessed, but is believed to still contain considerably fewer than 10,000 mature individuals.
The species inhabits regions of 'Satoyama', described as the natural environment between native nature and urban areas (Wild Bird Society of Japan [Tokyo] in litt. 2020). It breeds from suburban forest patches to heavily forested areas, including coniferous, broadleaved and degraded forest, on hills and the lower slopes of mountains (up to 1,500 m), where there are watercourses and damp areas. It winters in dark, deeply shaded forest near water up to 2,400 m. The preferable nesting trees are broadleaved trees such as Prunus and Quercus sp. (Ishikawa et al. 2012), while they nest on coniferous trees, such as pines and cedars, in some areas (Yamashina 1941, Kurahara 1990). It forages mainly in forest, but will use swamps, rice-fields and farmland and is mainly crepuscular. Breeding has been recorded from April to August (Komiya and Sugita 1975, Kawana 2006). A habitat model showed that precipitation and the number of abandoned rice fields were good predictors of occurrence for this species, with this habitat likely providing food source and nesting trees. Forest plantations were negatively associated with species occurrence (Hamaguchi et al. 2014). Earthworms are probably the principal food source, but land snails, cicadas, crabs, and ground and scarabid beetles are all present in its diet (Kawakami et al. 2005, K. Kawakami in litt. 2007, Oh et al. 2010).
The main threat was previously considered to be deforestation for timber and agriculture in both its breeding and non-breeding ranges. The drastic decrease in Japan since the 1960s also coincides with the period of a large decrease in forest area across wider Southeast Asia (Kawakami and Higuchi 2003). In the same period, summer visiting birds in Japan had decreased, although resident species were stable or had increased (Higuchi and Morishita 1999). Habitat destruction in the wintering areas is now considered as the main cause of population reduction. However, loss of forest floor vegetation and the subsequent loss of soil due to Sika Deer Cervus nippon may also affect viability of breeding populations in Japanese forests (S. Hayama in litt. 2020). Small-scale housing developments, solar power generation, cemetery development, and a general reduction in incentive to maintain biodiversity may also be negatively impacting some breeding sites (Wild Bird Society of Japan [Tokyo] in litt. 2020). The development of dense scrub undergrowth in forest and on abandoned farmland (following a change in traditional agricultural practices) is also believed to reduce the suitability of these habitats for feeding. It has probably been hunted in many parts of its range (including passage sites in northern Philippines and across its wintering area on Mindanao where it gets caught in snares; P. Simpson in litt. 2020, D. Allen in litt. 2020), and suffers from human disturbance (Anon. 2009). It declined rapidly on Miyake-jima in the Izu Islands, where it was formerly abundant, following the introduction of Siberian Weasel Mustela sibirica in the early 1970s. Today nest predation by corvids is an increasing threat as crow populations increase in urban and suburban areas.
Conservation Actions Underway
It is legally protected in Japan and Hong Kong. Birds may occur in protected areas in Japan and it has been recorded in Quezon National Park, Philippines. Environmental Impact Assessments are conducted prior to major developments in Japan, and if this species is identified using a site mitigation measures are taken (K. Kawakami in litt. 2007). The Japanese Ministry of Environment have additionally published ongoing guidelines for the conservation of the species since 2016 (K. Kawakami in litt. 2016).
Conservation Actions Proposed
Survey its breeding range in Japan and its wintering range in the Philippines. Establish a monitoring programme of its breeding and wintering populations. Study its home-range requirements using radio-telemetry. Protect and manage forests in its breeding and wintering grounds. Ensure official protection throughout its range and strengthen and enforce legislation to prevent the sale of this (and other threatened) species. Establish public-awareness programmes concerned with its conservation. Control and monitor invasive species where appropriate within its range.
49 cm. Small, stocky heron with stout bill. Rufous-brown head and neck. Black streaks down foreneck and breast. Chestnut-brown upperparts and wing-coverts with fine black vermiculations. Juvenile and immature has blackish crown, less rufous on head, more streaked neck, paler wing-coverts and white in primaries. Similar spp. Malayan Night-heron G. melanolophus has black cap and long crest, and shows white in primaries when flying.
Text account compilers
Fernando, E., Martin, R., Everest, J.
Allen, D., Benstead, P., Bird, J., Chan, S., Crosby, M., He, F., Kawakami, K., Khwaja, N., Kominami, Y., Kushlan, J., North, A., Ohata, K., Peet, N., Simpson, P., Taylor, J. & Wild Bird Society of Japan
BirdLife International (2023) Species factsheet: Gorsachius goisagi. Downloaded from http://datazone.birdlife.org/species/factsheet/japanese-night-heron-gorsachius-goisagi on 29/11/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 29/11/2023.