Geographic and Climatic Relationships of Avifaunas with Special Reference to Comparative Distribution in the Neotropics PAUL SLUD SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 212 SERIAL PUBLICATIONS OF THE SMITHSONIAN INSTITUTION The emphasis upon publications as a means of diffusing knowledge was expressed by the first Secretary of the Smithsonian Institution. In his formal plan for the Insti- tution, Joseph Henry articulated a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This keynote of basic research has been adhered to over the years in the issuance of thousands of titles in serial publications under the Smithsonian imprint, com- mencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Annals of Flight Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Studies in History and Technology In these series, the Institution publishes original articles and monographs dealing with the research and collections of its several museums and offices and of professional colleagues at other institutions of learning. These papers report newly acquired facts, synoptic interpretations of data, or original theory in specialized fields. These pub- lications are distributed by mailing lists to libraries, laboratories, and other interested institutions and specialists throughout the world. Individual copies may be obtained from the Smithsonian Institution Press as long as stocks are available. S. DILLON RIPLEY Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 212 Geographic and Climatic Relationships of Avifaunas with Special Reference to Comparative Distribution in the Neotropics Paul Slud SMITHSONIAN INSTITUTION PRESS City of Washington 1976 ABSTRACT Slud, Paul. Geographic and Climatic Relationships of Avifaunas with Special Reference to Comparative Distribution in the Neotropics. Smithsonian Contri- butions to Zoology, number 212, 149 pages, 37 figures, 11 tables, 1976.—A simple species list of birds contains within itself environmental information which is analogous to that obtained from a weather station. In both instances the numeri- cal data do not become meaningful until used comparatively. The Class Aves is divisible into passerines, comprising two-thirds of the world's land birds, and nonpasserines, comprising the remaining third. The passerines in turn are divisible into oscines and suboscines. The suboscines are numerous only in the Neotropical region, where they outnumber the oscines. Utilization of these major taxonomic components as though they were ecological assemblages is sub- stantiated on objective grounds for the mainland but is not justifiable for islands. In the neotropics, the relative proportions of the major taxonomic components correlate with the major dimatovegetational parameters of rainfall and tempera- ture to provide a comparative measure of faunal and environmental similarity or dissimilarity and of biotic complexity. The suboscine proportion is highest in the rain-forested Amazonian lowlands, thence decreases radially and altitudinally. The oscine proportion fluctuates to varying degree in the opposite direction from that of the suboscine proportion. The nonpasserine proportion decreases with increasing elevation to tree line and with increasing rainfall altitudinally and latitudinally. Crossplotted, the passerine-nonpasserine and suboscine-oscine relationships pro- duce a two-dimensional "map" on which to visualize the comparative distribution of neotropical avifaunas. Avifaunas having similar proportions of passerines (or nonpasserines) and of suboscines (or oscines) form into discrete climatic clusters. Any faunal level can be accommodated from the zoogeographic region down to the habitats at a study site, provided the comparisons are restricted to units of similar size. The smaller the size of the unit, the more precise is the avifaunal or environ- mental information it furnishes. Whether for purposes of comparison or predic- tion, equivalent samples from equivalent points at equivalent times of year are not only necessary but also feasible to obtain, and a simple methodology by which to accomplish this is presented. The proposition that site-oriented com- parisons in which the loci each approach a bioclimatic standard are fundamental to the choice, study, and preservation of representative natural areas is supported on theoretical grounds and by examples. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 6050. SERIES COVER DESICN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging in Publication Data Slud, Paul. Geographic and climatic relationships of avifaunas with special reference to comparative distri- bution in the neotropics. (Smithsonian contributions to zoology, no. 212) Supt. of Docs, no.: SI 157:212 1. Birds—Latin America—Geographical distribution. 2. Birds—Geographical distribution. S. Bioclimatology. I. Title. II. Series: Smithsonian Institution. Smithsonian contributions to zoology, no. 212. QL1.S54 no. 212 [QL689A1] 591'.08s [5985^8] 75-619130 Contents Page Introduction 1 Species Lists 2 Categories 2 Need to Compare Equal Areas 2 Elimination of Water Birds 2 Total Land Birds 5 Migrants 6 The Passerine-Nonpasserine Relationship 10 Recognition of the Relationship 10 Regional Diversity and Climate .. 11 Mainland Environmental Correlations 14 Islands 21 Area, Species and Ratio 22 Turnover 29 Island Types 33 Summary 50 The Suboscine-Oscine Relationship 50 Neotropical Distribution 51 Sample versus Compilation 56 Summary • 56 The Passerine-Nonpasserine Suboscine-Oscine Relationship 57 Comparative Categories 57 Single-Figure Values 60 Environmental Clusters 64 Summary 66 Requirements for Further Research 70 Sampling 70 Checklists versus Samples 70 Analytical Methods 70 Faunal Resemblance 79 Accuracy of Counts 80 Choice of Locale 81 Amazonia 81 Costa Rica 82 Appendix 1: Bibliographic Key to Geographic Units in the Tables and Figures 84 Appendix 2: Tables 90 Literature Cited 135 Geographic and Climatic Relationships of Avifaunas with Special Reference to Comparative Distribution in the Neotropics Paul Slud Introduction nonpasserines. This is a global relationship mak- ing it possible to compare the whole with its parts There are about 8650 living species of birds in and the parts with one another. Eliminating the the world (based on Austin, 1971). This total, dif- water birds serves to place the passerines (all of fering little from that of other recent authors or them land birds) and the nonpasserines (one- even from one compiled a generation ago by Mayr quarter of them aquatic) on the same terrestrial (1946), can be accepted as virtually complete. In- footing. A second set of relations is that between cluding extinctions in the last few centuries (based oscines and suboscines. This is primarily a neotropi- on Austin, 1971) the number rises to 8717. This is cal relationship, which is here further strengthened the figure used here, inasmuch as recently defunct and substantiated. The two sets of relations are con- species formed part of existing natural assemblages sidered separately, then together. Cross-plotted, and often appear in faunal works. they produce a two-dimensional distribution of Faunal works, or compilations, are for the most neotropical avifaunas. As an imitation of nature, part freely available in the printed literature (but the picture can be appreciated on its own merits or not, in my experience, when unpublished or pri- in relation to vegetation, climate, and topography. vate). The boundaries can be regional, geographic, The paper concludes with a rationale in which political, or ecological, the scope supracontinental avifaunal sampling and choice of locale are con- to local. Ranging from a set of volumes on a shelf sidered interdependent, provided the objective is to a pocket pamphlet or card, a compilation may the acquisition of comparative data. or may not inventory an area completely. The ones ACKNOWLEDGMENTS.—The American Museum of which do are the source of species lists that can be Natural History and the Carnegie Museum per- put to comparative use. mitted me to examine the extensive Amazonian On the basis of simple species lists, this paper ornithological materials in their care. At the Smith- attempts to point out elementary sets of avifaunal sonian Institution, H. Daniel Roth, formerly, and relations and to utilize these relations to compare Lee Ann Hayek, at present, in the Information avifaunas and to link them to their surroundings. Systems Division were instrumental in calculating One set of relations is that between passerines and correlation coefficients and regressions; Robert G. Tuck, Jr., formerly in the Department of Verte- Paul Slud, Department of Vertebrate Zoology, National Mu- seum of Natural History, Smithsonian Institution, Washing- brate Zoology, supplied species counts of reptiles ton, D.C. 20560. and amphibians in the eastern Caribbean area; SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY Robert H. Gibbs, Jr., Chairman of the Department As Table 1 demonstrates,