The collections which Mayr himself assembled in New Guinea and in the Solomon Islands as well as those from the Pacific Ocean, Malay Archipelago, southeastern Asia and other areas which he studied at the AMNH came from many remote and ornithologically poorly known regions of the world. Therefore they contained an unusually large number of unnamed taxa of birds, new subspecies as well as new species, as I repeatedly mentioned above (Fig. 4.11). Among the total of 471 new taxa which Mayr named between 1927 and 1960 (and two nomina nova in 1986) are 26 new species (the description of one additional species was barely anticipated by Japanese authors) and 445 subspecies. Every new form was carefully studied and compared before it was named. If he had any doubts he walked over to John Zimmer, an expert on subspecies differences, who sat only 20 steps away
from Mayr and he named only forms which Zimmer approved of. Admittedly, like the best taxonomists of the day, he was also a splitter. Several of Mayr's newly described subspecies, particularly among the insular forms, probably will be raised to species status when more details on their life history and behavior are known, e.g., Phalacrocorax melanoleucos brevicauda, Eurostopodus mystacalis exul, and others. Mayr described 376 taxa (including 26 species) alone and 95 in coauthorship with his colleagues A. Rand (33 taxa) during the 1930s, D. S. Ripley (15 taxa) in 1941, andT. Gilliard (29 taxa) during the 1950s. Other coauthors with whom he described one or several new subspecies were Birckhead, Greenway, Serventy, Meyer de Schauensee, K. Jennings, Gyldenstolpe, Van Deusen, and McEvey. From the birds which Mayr collected in former Dutch New Guinea, Hartert (1930) described three valid new species and 28 valid new subspecies.
Like many contemporary ornithologists (e.g., Hartert, Stresemann) Mayr also delimited polytypic species taxa rather broadly, in a few cases including in one species an allopatric representative as a new subspecies which, on the basis of additional evidence, is considered a full biological species by today's somewhat narrower standards. Examples are Phalacrocorax melanoleucos brevicauda Mayr 1931 (Rennell Island), possibly Eurostopodus mystacalis exul Mayr 1941 (New Caledonia), and also Rallina rubra [leucospila] mayri Hartert 1930 (northern New Guinea). The number of full biological species described by Mayr will probably increase when, in the future, genera of birds will be revised which comprise well-differentiated subspecies that he described. Of course, such taxa represent phylogenetic "species" under that "species" concept (p. 204).
The authors of J. L. Peters' Check-list of Birds of the World (1931-1987) accepted most of Mayr's new taxa. They and several authors of more recent monographs combined (synonymized) only 26 of Mayr's 445 subspecies with previously described forms. Among the authors of the Check-list is also Ernst Mayr himself who synonymized or accepted the synonymy of 12 forms which he had described in previous years (among which are five in Pachycephala and two Amblyornis bower-birds). B. P. Hall synonymized a Mayr subspecies in Pericrocotus ethologus, G. Mees synonymized four other Mayr subspecies in the following species: Rallina tricolor, Charmosyna placentis, Cinnyris sericea, and Zosterops novaeguineae. C. Vaurie did the same with one form in Cecropis striolata. In one case (Melanocharis striativen-tris albicauda) an earlier available name was found. Seven forms, one in each of the following species, need additional study and are, at best, "weak" subspecies: Butorides striatus, Rallina tricolor, Ducula aenea, Micropsitta bruijnii, Prunella rubeculoides, Staphida castaneiceps, and Melidectes leucostephes (M. LeCroy, pers. comm.).
One reason for the high percentage of valid taxa in Mayr's work, besides his clear principles for recognizing subspecies, is the fact that he dealt mostly with island faunas composed of geographical isolates. Populations on islands often show more clear-cut geographical variation compared to continental faunas and to a lesser extent smooth and gradual variation; if so, it is in the form of a stepped cline. Smooth clinal variation of continuous continental populations often presents more problems for a subdivision into discrete subspecies than island faunas and, therefore, leads to more disagreement among workers about the validity and delimination of certain subspecies.
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