Vocalisations in Philippine Hawk Owl have revealed that the species should really be treated as eight forms, including seven full species.
Though similar in plumage, the endemic Ninox philippensis sensu lato has been shown to be polyphyletic (that is, holding more than one lineage) by an academic team. Interestingly, in line with many other splits in the last few decades, this mostly correlates with the seven species originally named from the archipelago in the 19th Century, though the species has been treated as one since 1945.
The team's analysis of vocalisations and plumage found there to be three main clades, containing seven species and five subspecies; two new species have been described, along with at least one new subspecies.
The new taxa are as follows:
All-streaked underparts and plain crown
Luzon Hawk Owl N philippensis
N p philippensis - most of the large central to northern islands
N p ticaoensis - Ticao
N p centralis - Siquijor
Barred breast, streaked lower underparts and spotted crown
Mindanao Hawk Owl N spilocephala - Mindanao and other major southern islands
Barred to almost plain underparts
Mindoro Hawk Owl N mindorensis - Mindoro
Romblon Hawk Owl N spilonota
N s spilonota - Sibuyan
N s fisheri - Tablas
Cebu Hawk Owl N rumseyi - Cebu
Camiguin Hawk Owl N leventisi - Camiguin Sur
Sulu Hawk Owl N reyi - Sulu and other extreme south-west islands
Though not confirmed by molecular analysis, this should be forthcoming and the taxa appear to correlate well with the biogeographical barriers and limits predicted on the islands and shown to apply to many other endemic forms.
These distinctions underline further the recently divined cryptic radiations that have occurred in the complex archipelago, and will make birding visitors to the islands get out their notebooks once more. Five of the species at least are considered to already be endangered.
Rasmussen, P C, Allen, D N S, Collar, N J, DeMeulemeester, B, Hutchinson, R O, Jakosalem, P G C, Kennedy, R S, Lambert, F R and Paguntalan, L M. 2012. Vocal divergence and new species in the Philippine Hawk Owl Ninox philippensis complex. Forktail 28: 1-20.