Melanesia's birds, by its great evolutionary biogeographers


Mayr, E. & Diamond, J. (2001) The birds of Northern Melanesia – speciation, ecology, and biogeography. Oxford University Press, Oxford, UK. xxiv + 492 pp., figs., tables, maps, 9 colour plates, subject index, species index. Hardback: Price £45.00. ISBN 0-19-514170-9.

Ernst Mayr and Jared Diamond are well known as fathers of evolutionary biogeography theory. Less well known is that many of these theories were based on their vast personal knowledge of Melanesian birds — Mayr spent decades firstly in the field and then analysing the Whitney South Seas Expedition specimens, and Diamond has undertaken 19 fieldwork expeditions to the region. This book synthesizes their data and conclusions on the speciation, ecology, dispersal and biogeography of Melanesian birds.

The backbone is a formidable dataset on the birds of Northern Melanesia – the Bismarck and Solomon archipelagos off New Guinea. Comprehensive data are collated on 195 ‘zoogeographic’ species breeding across 76 islands of varied geographical characters. This book thus contains possibly the biggest dataset of its kind, meticulously reviewing all the distributional data collected in the period 1823–1999, most notably including a decade of Whitney expeditions and many decades of Mayr and colleagues documenting these specimens. This dataset contains many unpublished records from the Whitney expedition diaries, the authors’ fieldwork and reports from local villagers interviewed by Diamond, though these are not specifically labelled as such. Whilst these reports appear to be reliable, it would be useful to reference the sources. This raw distributional data, and the authors’ calculations of basic ecological and evolutionary indices (e.g. level of endemism, origins, dispersal and abundance) for individual species and islands, fill 70 pages of appendices. Our knowledge of species distributions is surprisingly complete, thanks largely to the dedication of the early collectors risking endemic malaria and cannibals. The calculated ecological and evolutionary indices are based on less-comprehensive data, but are also impressively accurate. The most instructive distributional patterns are illustrated in 52 large and clear maps, and colour plates illustrate the 88 most interesting examples of radiating and endemic taxa. Whilst not seeking to function as an identification guide, the paintings provide the reader with an effective grasp of the beauty and reality of the theories discussed herein, and stimulate the browser to investigate more closely.

The 309 pages of main text analyse this dataset with regard to biogeography and speciation, identify trends and general rules, identify and try to explain the exceptions, and investigate modified rules. The species-based analyses and examples are based on Mayr's extensive Whitney expedition papers (most of which were published in the period 1931–57), and most of the biogeographical generalizations are a synthesis of Diamond's papers from the 1970s and 1980s. The impression that much of this content is old is underlined by the continued use of outdated geographical names, such as the colonial New Hebrides for the long-independent nation of Vanuatu. These analyses are supported by regression models and statistics where relevant. The statistical calculations are often abbreviated, enabling a flowing text uninterrupted by figures, but sometimes leaving the reader wishing for further detail. The authors aim for a middle ground of realistic generalizations, and warn that their greatest generalization is that these taxa do not fit neat rules. They ask questions such as: why have certain taxa speciated more readily than others? They talk the reader through layers of analyses and show that these ‘great speciators’ are abundant and have intermediate ‘vagility’, where they calculate ‘vagility’ from a number of measures of dispersal.

The authors eloquently discuss different levels of speciation and the arbitrary decisions needed to define taxonomic units at any taxonomic level. Many geographical analyses are based on ‘zoogeographic’ species: distinctive species plus superspecies, but omitting the allospecies, which are such a predominant feature of this avifauna. Whilst this makes sound geographical sense, it will cause some confusion for readers familiar with conventional species. However, many analyses are repeated for the different taxonomic levels of superspecies, allospecies, megasubspecies and (poorly-defined) subspecies, which increases sample sizes and strengthens conclusions, but at the cost of frequent repetition. Wider comparison with other avifaunas, notably the taxonomically related New Guinea avifauna, or from Wallacea and the Philippines — the other great archipelagos of speciation — would either improve sample sizes and confidences, or allow independent testing of hypotheses.

The book serves its purpose well, as a thorough but accessible synthesis of these authors’ many classic papers, analyses and theories. Whilst it may not present any grand new ideas, the authors do suggest a number of directions for further research, based on their database: molecular investigation into taxonomic relationships and evolutionary time-scales (no molecular work has been published so far for North Melanesian birds); collecting subfossils for evidence of historical extinctions and extirpations (very limited work suggests a significant effect although far less than in Polynesia); checking the few unstudied historical texts (which may indicate extinct populations); collecting field data to enable better calculation of abundance and vagility; a few cases for collecting further specimens; and many analyses that can be improved or extended either within this dataset or by using other regions or taxonomic groups. From the conservationist's perspective, it is hoped that this book will inspire more interest, local and international, in this neglected yet fascinating region, and its equally neglected conservation problems of logging, oil-palm conversion and the underlying development pressures.