Voous K.H. & Payne H.A.W. (1965) The grebes of Madagascar. ARDEA 53 (1-2): 9-31

Three species of small grebes or dabchicks are reported from Madagascar. Two of these are endemic breeding birds: Podiceps pelzelnii and P. rufolavatus. The first of these species was described by Hartlaub as early as 1861 and is generally recorded as common throughout the island in suitable fresh water localities. The second species was described by Delacour as late as 1932; it is only known from Lake Alaotra. A third species, P. ruficollis (African race capensis), was for many years considered as rare in Madagascar, where it was not known as a breeding bird. Delacour (1933) could only list 5 stray specimens in old collections. In 1945 Milon (1946) found it numerous on Lake Anosy near Tananarive. The occurrence of more than one species of small grebe of almost similar size and proportions in one island presents problems of systematic, zoogeographic and ecologic interest. Therefore, Mrs. H.A.W. Payne visited Madagascar in May-July 1960, where she collected 44 specimens of grebes of all three species, in addition to distributional and ecological data. P. pelzelnii was found to be the rarest of the grebes. At least five times as many P. rufolavatus were seen as pelzelnii. P. ruficollis was by far the commonest species. On account of juvenile birds collected, which apparently had been unable to make long flights, P. ruficollis was considered to have nested in Madagascar. The presence of intermediate specimens of ruficollis and rufolavatus in the series collected on Lake Alaotra was considered to provide sufficient evidence for a theory of hybridization of these species. All three species occurred alongside each other at Lake Alaotra, and apparently also had nested there. Differences in proportions of length of bill and wing indicate that pelzelnii and rufolavatus are ecologically slightly distinct: P. pelzelnii being a long-winged, short-billed species, P. rufolavatus being short-winged and long-billed. P. ruficollis is in between; it therefore seems to be in a position to disturb the ecological balance between the two first named species. In comparison to continental ruficollis it has, however, on the average a longer bill, which it may have acquired in Madagascar, either through hybridization with rufolavatus or through competition with pelzelnii. Mrs. Payne collected specimens intermediate between rufolavatus and ruficollis in various stages of plumage. Examination in the Paris Museum showed that in some characters the type specimen of rufolavatus is also intermediate with ruficollis and therefore probably is a distant hybrid. It also appeared that the material collected by the French-British-American expeditions to Madagascar under Delacour's direction contained one immature ruficollis and two or three specimens of supposed hybrid origin. So far, all intermediate specimens known originate from Lake Alaotra. A theory is developed on the origin of the species of grebes at present breeding in Madagascar, and a tentative prognosis is given of the future development of this unique situation. Probably the oldest species is pelzelnii. It is expected to have a hard time to maintain itself against a spreading population of ruficollis. The next oldest species is P. rufolavatus, which is thought to have acquired its present, striking characteristics during a long period of insular isolation of colonists of an old, African ruficollis-stem. P. ruficollis is the most recent African colonizer, probably from this century. It is now spreading rapidly throughout Madagascar, where it may have found favourable opportunities in connection with the destruction of original habitats and the presence of permanent artificial water reservoirs. In view of the supposed hybridization of P. ruficollis with P. rufolavatus on Lake Alaotra the authors fear that the present form rufolavatus will ultimately become merged into a stabilised hybrid population. The latter, as well as the present polymorphic population, will remain to be known as P. ruficollis rufolavatus. The original, long-billed, light-headed, yellow-eyed 'rufolavatus'-population will in that case be in need of a new name.