Abstract
Propithecus verreauxi is currently divided into three or four subspecies. Decken's sifaka, P. v. deckeni, and the crowned sifaka, P. v. coronatus, are believed to be synonymous by some authors, while others regard them as separate subspecies. The results of a survey on an isolated melanistic population of Decken's sifaka, known from museum specimens collected in Ambararatabe, as well as the results of additional surveys carried out within the ranges of P. v. deckeni and P. v. coronatus are presented. A detailed description and photographs of the melanistic variant are provided. The data are employed to argue the case for recognition of the subspecific status of the endangered P. v. coronatus. The consistency of sightings of P. v. coronatus to the east of the river Mahavavy and to the west of the river Betsiboka, and sightings of P. v. deckeni to the west of the Mahavavy indicate clear separation of the two subspecies in the lower reaches of two rivers. Clarification of the status of the enigmatic museum specimens from Ambararatabe, representing a melanisticform rather than hybridization of P. v. deckeni and P. v. coronatus, lends further support to this argument
Curtis, Deborah J