Species limits in the genus Bleda Bonaparte, 1857 (Aves, Pycnonotidae)

African forest bulbuls of the genus Bleda are usually placed into three separate species: B. syndactyla and B. eximia distributed both in Upper and Lower Guinea forest blocks, and B. canicapilla restricted to the Upper Guinean one. Acoustic data lead to question traditional morphologically-based species limits in this genus. Colouration patterns and measurements, particularly bill shape and length, wing and tail lengths, are reconsidered for all taxa. Multivariate (discriminant functions) analyses lead to separate nominate B. eximia as an Upper Guinean species distinct from Lower Guinean B. notata. Furthermore B. eximia appears closer to B. syndactyla than to the other two species. Acoustically, by the physical traits of their calls and songs as well as the behaviour associated with their production, B. eximia and B. syndactyla are very close and quite different from B. canicapilla and B. notata which constitute another pair of very close species. Obviously, in the frame of the biological species concept, the four taxa branched in two groups from a common ancestor, B. eximia and B. syndactyla represent a species-pair whereas B. notata and B. canicapilla are allospecies of a single superspecies. Allopatric speciation patterns based on alternate fragmentations and unitings of forests can be drawn from present knowledge of African forest history in relation to Pleistocene-Holocene events. However, a brief review of recent data on interspecific genetic differentiation in birds suggests an important discrepancy between biogeographical and molecular time calibrations. The development of molecular studies appears as a priority for the understanding of the evolution of African tropical forests birds.