The high number of species in the tropics permits two interpretations, an ecological and a genetic one. According to the genetic one, certain processes are active in the tropics (e.g. increased mutation rates or a speeding up of the number of generations) which accelerate the process of the multiplication of species. According to the ecological one, the tropical environment favours the accumulation and continued coexistence of an exceptionally high number of species, produced by the orthodox speciation process.The analysis of bird speciation favours a largely ecological interpretation. There is no evidence that speciation in the tropics differs in principle from that in the temperate zone. An alternation of dry and pluvial periods during the Pleistocene, together with continued if not accelerated mountain building in South America, south‐east Asia, and New Guinea, resulted in the steady production of numerous geographical isolates some of which completed the speciation process.Ecological factors may accelerate the rate of speciation in the tropics. This includes the possibility of a greater sedentariness of populations and a correspondingly greater efficiency of geographic barriers. It includes perhaps a greater narrowness of ecological niches and consequently a better chance for a new species to carve out a niche in an already rich fauna.Among populations coexisting in a geographical isolate, only a small percentage seem to complete speciation. The others either fuse again with the parental species when the geographical isolation ends or become extinct. Size of the speciating population and its ability to find a new niche seem to be crucial for success.All guesses as to which recent species owe their origin to what particular past climatic events, must be considered as highly speculative. The unambiguous establishment of such correlations has so far been unsuccessful, at least so far as birds are concerned. Absolute figures for rates of speciation cannot be give