The Calayan rail (Aptenorallus calayanensis) is a flightless bird of the rail, moorhen, and coot family (Rallidae) that inhabits Calayan Island in the Philippines. It is the only member of the genus Aptenorallus. Though well known to natives of the island as the "piding", it was first observed by ornithologist Carmela Española in May 2004 and the discovery was officially announced on August 16, 2004. The formal description as a species new to science appeared in the journal Forktail (Allen et al. 2004). Taxonomy Prior to 2022, it was classified in the genus Gallirallus. Following studies in 2012 and 2013, all recent species in the genus Gallirallus aside from the Calayan rail and the weka of New Zealand were moved to the genus Hypotaenidia. Following this, the Calayan rail and the weka were considered the two extant species of the genus Gallirallus. However, a 2021 phylogenetic study found the Calayan rail to be basal to the species classified in Habroptila, Eulabeornis, Gallirallus, and Hypotaenidia, and thus classified it into its own genus, Aptenorallus. This was accepted by the International Ornithological Congress in 2022. Description The Calayan rail is a relatively large flightless rail. Its plumage is dark grayish overall, with a blacker face and slightly browner upperparts. The bill and legs are bright orange-red, unique among similar-sized dark-colored ground-dwelling birds on Calayan. Its vocalizations are loud, harsh, and nasal-sounding. Habitat and conservation status It is found on the primary and secondary forest on coralline limestone areas on Calayan. IUCN has assessed this bird as vulnerable with an estimated population of just 2,500 to 4,300 mature individuals. It was initially estimated by biologists in 2004 that there were just 200 pairs on the island. It has since been found to be locally common, with an estimated area of occupancy of 36 km2. However recent species distribution modelling estimated its area of occupancy at 90.2 km2 . The species' main threat is habitat loss with the clearance of forest habitats as a result of logging and agricultural conversion within its range. It is also occasionally caught in snares meant for red junglefowl. It is also threatened by introduced species such as cats, dogs and rats which could prey on these birds and their nests. The Calayan municipal council has passed Municipal Ordinance No. 84, which prohibits the capture, sale, possession and collection of the species. There are currently many awareness campaigns using