Pachycephala means 'thick head' and this trait is indeed visible, if mildly, in the only member of the genus in Singapore. Variously placed in their own family (Pachycephalidae) or within the corvids, whistlers and their close relatives the shrike-tits, shrike-thrushes and toxic pitohuis are passerines that have invaded the Indo-Pacific from their stronghold in Australasia. As many as eight species of whistlers roam the southern continent – some are generalists at home in open habitats, while others are restricted to malee scrubland, dense woodland or coastal forests. A few are grey-brown things with buff throats and underparts while others, at least the males, bear distinctively black heads and breastbands and underparts that span gold, rufous and white.
What they lack in looks the birds make up for with a repertoire of calls that pierce the damp layers of wooded canopies and force a note of sweet sharpness into the dark understorey. It's probably not a coincidence that the mangrove whistler is dubbed murai bakau by inhabitants of the Malay Peninsula who were struck by its song and christened it after native thrushes already renown for their musical prowess. A bird of coastal swamps and casuarina stands, Pachycephala grisola is a plain creature with a stocky head and bill that would escape notice were it not for a voice of rare exuberance. Synchopated chirrups alternate with inflected whistles and explosive whip-cracks that work towards a grand tutti of one emphatic snap. Once "fairly common" throughout local mangroves, the whistler has followed its haunts into near-oblivion as the island's natural shores gave way to artificial beaches and largely lifeless walls. Hounded to the peripheries of the land as well as the fringes of caged imagination, the thick-headed singer now sallies for insects in the treetops of offshore refuges such as Tekong, Hantu and a landfill where the secrets of a sea people lie scattered and silent under a bedrock of ash.