This discussion was first published as part of the 2017 Red List update. At the time a decision regarding the status of several was pended, but to enable potential reassessment of these species as part of the 2018 Red List update this post remains open and the date of posting has been updated.
Celestial Monarch Hypothymis coelestis is endemic to the Philippines. Most recent records come from Mindanao (R. Hutchinson in litt. 2016), but there have been records also from Luzon, Negros, Sibuyan, Samar, Dinagat, Basilan and Tawitawi (Collar et al. 1999, B. Tabaranza in litt. 2007). It inhabits lowland forest, secondary forest and forest edge up to 750m, but usually lower, and this means that it is highly threatened by logging activity in the region. This deforestation has been extensive across the islands where this species has been reported, and particularly impacts lowlands. On Negros the remaining forest cover had declined to only 4% of its original on Negros by the late 1980s, 24% on Luzon and 29% on Mindanao. On top of this much of the remaining forest is under logging concessions or being considered for mining. Therefore, the species has been considered to be undergoing a rapid decline.
The population size has also been estimated to be small (2,500-9,999 mature individuals, with <1,000 mature individuals per sub-population), which together with the rate of forest loss led to this species being listed as Vulnerable under criteria A2c+3c+4c; C2a(i). Much of the habitat loss within its range occurred >3 generations (c.12.5 years) ago and a reassessment of habitat loss (Tracewski et al. 2016) suggests that the rate of decline may no longer approach the threshold for listing this species as Vulnerable under criterion A (>30% decline in three generations). However, it has been suggested that the population size of this species may in fact be far smaller than that currently estimated (S. Mahood in litt. 2013, R. Hutchinson in litt. 2016, A. Dwarshuis in litt. 2016). Early collectors in the region considered the species to be rare, though in 1959 it was reportedly commoner on Basilan and Sibuyan than it was on Negros. Now, however, the subspecies rabori, which is endemic to the Visayas, is likely to be extinct (it has not been recorded on Negros since 1959 and was not found in searches of Sibuyan in the early 1990s or subsequently [del Hoyo et al. 2006]), and the species may have been disappeared from Basilan too. The majority of recent records come from near Bislig, in the PICOP forest, on Mindanao, with only scattered records from elsewhere (eBird 2017, R. Hutchinson in litt. 2016). Thus, it is highly plausible that the population size may be <2,500 mature individuals, and could be placed in the range 1,000-2,499 mature individuals. However, to qualify as Endangered under criterion C2a(i) the largest sub-population must contain <250 mature individuals. Based on low population density estimates for congeners and assuming only a proportion of habitat is suitable/occupied would mean that this population may still contain >500 mature individuals, which would instead qualify the species as Vulnerable under criterion C2a(i). It should be noted that this forest has suffered from habitat loss and degradation due to planting of invasive trees for paper production, logging under concession and illegal logging. As such, the species may have been more heavily impacted in this area and population densities may be far lower than those used.
We therefore request any further information regarding the main sub-population on Mindanao, as even though the species now may number <2,500 individuals, being separated into different sub-populations by living on separate islands means it would not warrant listing as Endangered unless this main sub-population contains 95-100% of the population or <250 individuals. If this is not the case, the species would continue to warrant listing as Vulnerable under criterion C2a(i).
Collar, N. J.; Mallari, N. A. D.; Tabaranza, B. R. J. 1999. Threatened birds of the Philippines: the Haribon Foundation/BirdLife International Red Data Book. Bookmark, Makati City.
del Hoyo, J.; Elliott, A.; Christie, D. 2006. Handbook of the Birds of the World, vol. 11: Old World Flycatchers to Old World Warblers. Lynx Edicions, Barcelona, Spain.
eBird. 2017. eBird: An online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, New York. Available: http://www.ebird.org. (Accessed: April 5, 2017).
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.