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Zoogeography of the Irenidae (Aves: Passeres)

1974; Wiley; Volume: 6; Issue: 3 Linguagem: Inglês

10.2307/2989649

1744-7429

Daphne F. Dunn,

Ecology and Vegetation Dynamics Studies

The only family of birds endemic to the Oriental zoogeographical region is the Irenidae (genera Irena, Chloropsis, and Aegithina). The ranges of the 57 races (in 14 species) are described, and some taxonomic and distributional questions are raised. The southern Malay peninsula and Sumatra contain the largest number of species and subspecies, with numbers decreasing outward to their lowest values at the peripheries of the family's range. Several lines of evidence indicate that Malaya-Sumatra has served as the center of evolution of the Irenidae. Water gaps are important barriers to dispersal of birds of this family in which 28.6% of the species and 43.9% of the races are confined to a single island or island group. Mountains also impede dispersal, but ecological factors associated with altitude; latitude, and precipitation are probably more important that elevation per se. Much of the diversity of the Irenidae fauna in the Malaysian subregion may be attributable to Pleistocene sea-level oscillations. Some races and even species probably have evolved since the end of the last glaciation 11,000 years ago, making insular southeast Asia a natural laboratory for the study of bird evolution. Suggestions are made for ecological, ethological, zoogeographical, and taxonomic research to explain the restriction of this family, AUTHORITIES DISAGREE about the precise number of families of birds in existence, but it is generally regarded as approximately 170. Of the 144 families of land birds considered by Barden (1941), 33 occur in all six zoogeographical regions. The Nearctic, Palearctic, and Oriental regions have only one indigenous family each, while the other three regions exhibit considerably more endemicity (Pettingill 1970; Welty 1963), although because of taxonomic and distributional problems, even these generalizations are not accepted by all authorities (e.g. Darlington 1957; Van Tyne and Berger 1959). The more recent treatments of the subject, however, recognize one family of Aves that includes the fairy bluebirds (Irena), the leafbirds (Chloropsis), and the ioras (AegithinnazAethorhynchus) as being endemic to the Oriental zoogeographical region. Particularly in the early literature these genera were often classified within the family Pycnonotidae (bulbuls) (e.g. Caldwell and Caldwell 1931; Chasen 1935), which presumably accounts for Barden's (1941) listing of no family endemic to the Oriental region. When recognized as a separate family, this assemblage of three genera has been referred to as either Aegithinidae or Irenidae. Delacour used the former term in his books of 1946 (with Mayr) and 1947, but the latter in his contribution to Mayr and Greenway (1960), Ripley (1961), and Wildash (1968) also used Irenidae. Wetmore (1960) stated that the generic name Chloropsis antedates the others, hence should be used to designate the family, but he also placed Irena in the family Oriolidae (old world orioles) so that his family Chloropseidae included only Chloropsis and Aegithina. Other arrangements include that of Henry (1971) in which Irena is the sole genus of the Irenidae, the other two genera constituting the subfamily Liotrichinae of the Pycnonotidae, and that of Robinson (1927) in which the Irenidae comprise Irena and the nowsynonymized genus Ire-nella while the Aegithinidae consist of Aegithina and Chloropsis. I shall follow the majority of recent authors in considering Irena, Aegithina, and Chioropsis as comprising the family Irenidae. Aside from taxonomic studies and brief discussions of the species in bird guides, very little has been written about this group, although Ali and Ripley (1971) have recently enhanced our knowledge of the Indian forms. It is hoped that this review will raise questions that will prompt further research into the systematics of the Irenidae, as well as the ecology and ethology with a view toward explaining their distribution. Although the familial position of the genera may have been a subject of some dispute, the genera themselves and the species (with two possible exceptions) seem welldefined. Their geographic distributions are also quite well-known. However, systematics at the subspecific2 level, often based on subtle and apparently variable plumage differences (Hall 1957; Hoogerwerf 1962; Marien 1952; Robinson 1927), are to some extent not yet clear, particularly for Aegithina. The most general consensus of opinion is on races confined to islands or island groups. In this paper I shall, with a few exceptions, accept as valid those recognized as distinct by Delacour (1960), 1 Present address: School of Biological Sciences, University of Malaya, Kuala Lumpur, Malaysia. 2 The terms subspecies and race (i.e. geographical race) are used synonymously (Mayr 1969b). BIOTROPICA 6(3): 165-174 1974 165 This content downloaded from 157.55.39.35 on Wed, 31 Aug 2016 04:29:06 UTC All use subject to http://about.jstor.org/terms whose listing agrees with most recent literature on the subject. Aegithina are black and yellowor olive-green, mainly insectivorous birds; Chloropsis, bright green animals, are largely frugivorous, but feed on insects, nectar, and seeds as well; Irena, mainly blue in color, are almost exclusively fruit-eaters (Ali and Ripley 1971; Baker 1922, 1926; Hachisuka 1935; Robinson 1927; Smythies 1960; Whistler and Kinnear 1949). Thus all are tied to areas of abundant vegetation, occurring in forests, plains peripheral to forests, or areas of secondary growth, and most species are rarely resident much above about 1000 m elevation, although they may range higher (Ali and Ripley 1971; Baker 1922, 1926; Ripley 1961; Wait 1925). All are non-migratory although they may undergo altitudinal movements correlated with breeding season, so their ranges are strictly residential (Ali 1943; Ali and Ripley 1971; Deignan 1945; Whistler and Kinnear 1932). Irenidae range from extreme northwestern Pakistan to the easternmost portion of the Philippine Islands, and from the latitude of the Himalayan foothills south to Wallace's line, an area almost precisely coincident with that generally recognized as the Oriental region. However, no one genus spans the entire distance east to west, although all three genera extend to the northern and southern extremes of the range. Irena, the most geographically restricted genus, has only two species. The other genera have about equally wide geographic spans, but Aegithina extends farther west and Chloropsis farther east. Aegithina consists of four species, Chloropsis of eight. Nothing can be deduced about the zoogeography of the Irenidae at the generic level for all three genera are found in lower peninsular India and Ceylon, from Bangladesh eastward through Burma, Thailand, IndochiDa, and into the Malaysian subregion as far east as Palawan. Aegithina alone extends into Pakistan. while both Chloropsis and Irena are represented east of Palawan in the Philippines.