The species is found in patches of highly fragmented deciduous forest in western Madagascar between the Mahavavy and Manambolo Rivers. The southern limit of its range does not extend to the Tsiribihina River, which marks the northern limit of P. verreauxi. To the north, within the coastal forests that occur between the Betsiboka and Mahavavy Rivers, the geographic separation between P. deckenii and P. coronatus is clear, but not on both sides of the lower reaches of the Mahavavy where the changing river course allows the populations to interchange (Thalmann et al. 2002). More confusing is the situation in forests of the Bongolava Massif, where animals with colour patterns characteristic of both species have been observed; populations of both species also can be found at a number of other sites (Thalmann et al. 2002).