Justification of Red List Category
This jay has a small population which is suspected to have declined at least twice, as a result of over exploitation in the early 20th century and possibly as a result of increased levels of predation and forest development in the late 20th century. It therefore qualifies as Vulnerable. Lack of data makes determining current trends difficult. If systematic surveys reveal that the population is stable or increasing following predator control and forest regeneration, the species may warrant downlisting.
The global population is estimated to number c.5,800 individuals (Nishidi 1974 in Brazil 1991), equivalent to c.3,900 mature individuals. It has been suggested that the population now exceeds 5,800 individuals (K. Ishida in litt. 2012); however, further research is required. The population is presently assumed to form one sub-population, but future genetic research (K. Ishida in litt. 2012, 2015) is expected to confirm whether this is the case.
It has been suggested that the population is now stable (K. Ishida in litt. 2012), but until new data are available the trend is precautionarily assumed to be negative. Although forest loss is unlikely to be having a significant impact upon this species, reduced reproductive success owing to nest predation by mammals is perhaps still leading to a moderate decline overall.
Garrulus lidthi is endemic to the islands of Amami-ooshima, Kakeroma-jima, Uke-jima, Edateku-jima, part of the Nansei Shoto Islands, Japan (BirdLife International 2001, K. Ishida in litt. 2012). Its population was estimated at c.5,800 birds in the 1970s, but it may have declined through to the 1990s. It is precautionarily treated as undergoing a continuing decline overall, although it may have begun to increase since 2006, owing to alien predator control and natural forest regeneration (Yukihiro Kominami in litt. 2007), and may now be stable (K. Ishida et al. 2012, 2015, 2016). Some observations indicate a population increase in the northern Kasari peninsula of Amami-ooshima (M. Takashi per K. Ishida in litt. 2012).
It occurs from sea-level into the hills, in subtropical evergreen broadleaved forest, coniferous forest, and in woodland around cultivation and human habitation, showing a significant preference for mature forest. It feeds on and caches the acorns of Castanopsis cuspidate, Quercus glauca and other oaks when they are available; large acorn production is crucial to its breeding success (Ishida et al. 2015). If this food supply is exhausted birds will feed in agricultural fields (Yukihiro Kominami in litt. 2007). Sweet potato, insects, spiders, seeds, fruits, reptiles, including Okinawa pit-viper Protobothrops flavoviridis, and birds are also included in its diet. It forages in trees and on the ground. Breeding takes place from late January or early February until May. Twelve out of 30 adult birds were found to be positive for avian malaria parasites from surveys conducted 2009-2011, though in comparison to other species in the area, prevalence in this species is thought to be low (Ishida et al. 2015).
In some years, a high proportion of nests are predated by crows and mammals, and the small Indian mongoose Herpestes auropunctatus and snakes have been reported to prey on young birds and eggs. There are now low levels of H. auropunctatus on Amami island, but even with continued control, complete irradiation is unlikely for another decade (Fukasawa et al. 2013). It is not known whether this predation pressure will have a long-term effect on the population. The numbers of Large-billed Crow Corvus macrorhynchos on Amami-ooshima may have recently increased, probably because of increased garbage disposal on the island. The effect of logging on its population is probably relatively small.
Conservation Actions Underway
It is legally protected in Japan. Yuwandake on Amami-ooshima was established as a National Wildlife Protection Area, for the conservation of a range of species, including this species and the Amami Thrush Zoothera dauma major. Several surveys and ecological studies have been completed. Introduced small Indian mongoose has been controlled within its range in recent years and as a result the species may now be stable or increasing. The increase in numbers of Large-billed Crows Corvus macrorhynchos on Amami-ooshima has been halted by improvements in refuse management (K. Ishida in litt. 2012).
38 cm. Large, brown and blue jay. Dark blue head with blue-black forehead and lores. Dark blue tail. Rich chestnut back and underparts. White tips to flight and tail feathers. White flecking on throat. Bicoloured bill with horn tip and grey-blue base. Voice Unknown.
Text account compilers
Benstead, P., Bird, J., Crosby, M., Peet, N., Taylor, J., Martin, R, North, A.
Kominami, Y., Ishida, K., Mizuta, T.
BirdLife International (2020) Species factsheet: Garrulus lidthi. Downloaded from http://www.birdlife.org on 05/07/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 05/07/2020.