This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2014.
Calayan Rail Gallirallus calayanensis is restricted to Calayan island in the Babuyan islands, northern Philippines. It is currently listed as Vulnerable under criterion D2 because it has a very small range, restricted to <6 locations.
The population of this species was previously estimated at 100-200 pairs (Allen et al. 2004), but the latest estimate, based on species distribution modelling and known densities, put the population size at 3,800-6,500 individuals (C. Layusa and C. Oliveros in litt. 2012) which equates to 2,500-4,300 mature individuals. The relative abundance indices obtained from surveys in 2005–2010 fluctuated moderately (low of 0.301 rails/census station in 2006, high of 0.656 rails/census station in 2007) (C. Layusa and C. Oliveros in litt. 2012). In addition, the Area of Occupancy (AOO) was previously estimated at c.36km2, but recent species distribution modelling estimates its AOO at approximately 90.2 km2 (Layusa and Oliveros, unpublished data). However, it has also been suggested that the extent of this species’s habitat is continuing to decline (C. Oliveros and C. Layusa in litt. 2012). Analysis of satellite images from 1979 and 2006 showed an 8% decline in forest cover on Calayan Island, which could mean an 8-27% decline in the species’s range over this period (C. Layusa and C. Oliveros in litt. 2012). If confirmed, this species could warrant uplisting to Endangered under criterion B2ab(iii) of the IUCN Red List on the basis that its AOO is <500 km2, it is found in ≤5 locations and the extent of its habitat is continuing to decline. Nevertheless, in 2011, the Calayan municipal council passed an ordinance establishing the Calayan Wildlife Sanctuary, covering an area of 29 km2 of forest in the island’s interior (Layusa in litt. 2012). This sanctuary will protect one of the areas containing a dense population of the Calayan Rail (ISLA Biodiversity Conservation, 2008) and thus, could limit the predicted future declines in its habitat.
Further information is required on population trends, distribution and the severity of habitat loss within this species’s range, and we welcome any additional comments on the proposed uplisting.
Allen, D., Oliveros, C., Española, C., Broad, G. and Gonzalez, J. C. T. (2004) A new species of Gallirallus from Calayan island, Philippines. Forktail 20: 1-7.
ISLA Biodiversity Conservation. (2008) Establishing a wildlife sanctuary in Sitio Longog, Calayan Island: technical report.