J. Zool., Lond. (2001) 254, 207±218 # 2001 The Zoological Society of London Printed in the United Kingdom A comparative analysis of the avifaunas of different zoogeographical regions I. Newton and L. Dale Centre for Ecology and Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE 17 2 LS, U.K. (Accepted 12 July 2000) Abstract This paper provides a comparison of the landbirds of all main zoogeographical regions, based on the most recent (Sibley±Monroe) listing and classi®cation of the world's birds. This classi®cation arranges 9416 landbird species (i.e. excluding seabirds) into 2002 genera, 140 families and 23 orders. On this basis, the Neotropical region holds 36% of all known landbird species and 45% of genera, the Afrotropical region holds 21% of species and 24% of genera, the Indomalayan region 18% of species and 22% of genera, the Australasian region 17% of species and 23% of genera, the Palaearctic region 10% of species and 14% of genera and the Nearctic region 8% of species and 15% of genera. These major continental regions thus show 4.6-fold variation in species numbers or 9.1-fold variation in species numbers per unit area. The region of Oceania, comprising many Paci®c Islands, holds only 2% of the world's bird species and 4% of genera. About 92% of all bird species on the continental parts of the Neotropical, Afrotropical and Australasian regions are endemic to those regions, compared to 64% of the Indomalayan, 54% of the Nearctic and 46% of the Palaearctic species. The Oceania region has the smallest number of endemics, but these form 87% of all species occurring naturally in this region. About 91% of all landbird species breed in only one zoogeographic region, another 8% in two regions, with the remaining 1% in three to seven regions. Only four species breed in all seven regions. Similarities in the species composition of different regions were compared using Jaccard and Simpson indices. As expected, each region shares the greatest number of species with the closest other region and the fewest species with the most remote region. As in previous analyses, the Neotropical and Australasian regions emerged as having the most distinctive avifaunas. Regions that hold large numbers of landbird species also hold large numbers of genera and families, as well as high species-per-genus and species-per-family ratios. Comparable levels of diversity thus extend through all these taxonomic categories. This implies that, whatever factors have promoted particular levels of avian diversity in the different regions, they are of long standing. As found in previous studies, species-per-genus and species-per-family ratios are lower in island than in continental avifaunas. No relationship is apparent between the size of each zoogeographical region and the numbers of species, genera and families found there; rather those regions with tropical forest have many more bird taxa overall than those without. Key words: avifaunas, biogeographic regions, biodiversity, island birds, species numbers, zoogeography INTRODUCTION species numbers and of species similarities and differ- ences. Some of the most recent comparative accounts The species numbers, distributions and phylogenetic include those of Mayr (1994) for the Neotropical and relationships of birds are probably better known on a Nearctic regions, Keast (1972) for the Australasian, world scale than those of any other group of organisms. Afrotropical and Neotropical regions, and Udvardy This permits widescale biogeographical analyses to be (1958) for the Nearctic and Palaearctic regions. Several conducted for birds with greater precision and reliability other authors have provided assessments of the bird than is possible for most other types of organisms. faunas of individual regions (e.g. Vaurie (1959, 1965) Beginning with Sclater (1858) and Wallace (1876), for Palaearctic, Mayr & Short (1970) for Nearctic, attempts have been made to compare the avifaunas of Inskipp, Lindsey & Duckworth (1996) for Indomalayan, the different zoogeographic regions, both in terms of Moreau (1966) and Dowsett & Forbes-Watson (1993) 208 I. Newton and L. Dale Palaearctic rctic Palaeartic NeaNeartic Oceanian Oceanian Afrotropical Indomalayan Neotropical Australasian AntarcticAntartic Fig. 1. Main zoogeographical regions used in this avifaunal analysis. From various sources. for Afrotropical, Ridgely & Tudor (1989, 1994) for classi®cation have already been supported by subse- Neotropical), or for parts of regions, as in many area- quent work. Moreover, any modi®cations to bird restricted checklists and handbooks. classi®cation that might result from future work, while In this paper, we provide a comparative analysis of they might require some changes to the ®gures in our the landbirds of all the different zoogeographic regions, tables, are unlikely to greatly alter the main conclusions. using the most recent listing and classi®cation of the Our analysis is concerned only with landbirds (in- world's bird species (Sibley & Monroe, 1990, updated cluding both terrestrial and freshwater forms, but version by Sibley 1996 on CD-ROM), and also calculate excluding marine forms), a total of 9416 species ar- statistical measures of regional similarities. For the ranged in 2002 genera, 140 families and 23 orders. For breeding birds of each region, comparisons are made at these birds, we calculated the number of species, genera, four different taxonomic levels, of orders, families, families and orders that are known to breed in each genera and species. zoogeographic region and the numbers of species, The species list of Sibley & Monroe (1990) was genera, families and orders that each region shares with arranged under the classi®cation of orders and families each other region. Then, at each of these four taxonomic produced by Sibley & Alquist (1990), based mainly on levels, we calculated indices of similarity between each the method of DNA±DNA hybridization. For the lower pair of zoogeographic regions. This provided, at each taxonomic levels of genera and species, Sibley & taxonomic level, a measure of the degree of resemblance Monroe (1990) used as a basis the most recent available between the avifaunas of different regions. We also revision of each group. However, no analysis of this calculated the number of endemic taxa in each zoo- type can ever be de®nitive, because of the continual geographic region. The ®ndings are discussed brie¯y in (slow) discovery of new species, and more particularly relation to the known zoogeographic histories of each because of the continual taxonomic revision and re- region. grouping of already known forms. Aspects of the Following the usual zoogeographical convention, six Sibley±Alquist classi®cation have been challenged, and main regions were recognized, namely Palaearctic, some groups have been subject to more recent revision. Afrotropical (formerly Ethiopian, Benson et al., 1979), Nevertheless, we have opted to stick with the Sibley± Indomalayan (formerly Oriental, Clark et al., 1988), Monroe list because the CD-ROM version is still the Australasian, Nearctic and Neotropical, with approxi- most recent and complete, because it applied similar mate boundaries as shown in Fig. 1. In each region we taxonomic criteria throughout, and because some of the followed what seemed to be the most usual conven- initially controversial ®ndings in the Sibley±Alquist tion for birds, with the border between the Nearctic± Zoogeography of birds 209 Neotropical regions corresponding to the northern limit the main continental landmass (some of the latter also of the tropical forest in Mexico, that between the occur on islands). From these lists we could calculate Indomalayan and Palaearctic regions corresponding to the numbers of species occurring in each region, and the the Himalayan mountain chain and Yangtze River, and number shared between each region and each of the that between the Indomalayan and Australasian regions other regions. We could also calculate the numbers of corresponding to Wallace's Line running north-east species occurring in different numbers of regions from between the islands of Bali and Lombok and between 1 to 7 (including Oceania). The same procedure was Borneo and Celebes (Sulawesi). The eastward limit of repeated for each genus, family and order. Australasia was drawn so as to include the islands of One way to compare the avifaunas of 2 regions is to New Ireland, Solomons, New Hebrides, New Zealand, calculate the number of taxa they have in common. But Chathams and Campbell, while other Paci®c Islands this procedure takes no account of the total number of eastward almost to Galapagos were grouped as a taxa in each region, and the proportion of the total that seventh region, Oceania. The Galapagos Islands shared taxa form. To take account of these aspects, themselves were classed as Neotropical. various indices of similarity have been devised (Cheat- Between each of these regions, the landbird fauna ham & Hazel, 1969; Pielou, 1979; Brown & Gibson, intergrades, and drawing the lines between regions in 1983). We chose to use 2 different indices, namely those somewhat different positions (as some authors have of Jaccard (1901) and Simpson (1940), because they are done) would make small differences to the species totals the most different of all indices from one another. All in the tables, but would not affect the main conclusions. other indices known to us are functionally related to For the purposes of this paper, we have considered each one or other of these 2 indices,