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THIRD REVISED EDITION
Pages 20 – 23
CLASSIFICATION OF THE PARROTS
Within an order such as the Psittaciformes further categories are used by systematists to classify members of that order according to the suspected relationships and evolutionary patterns.
FAMILY (name ending in ‘-idea’) is a primary taxonomic category and subdivision of the order; parrots usually are placed in a single family, and this also reflects their homogeneity.
SUBFAMILY (name ending in ‘-inae’) is a secondary category interpolated between family and genus to differentiate broad groupings of apparently related genera.
TRIBE (name ending in ‘-ini’) also is a secondary category used to identify subgroupings of more closely allied genera.
GENUS (plural genera) is a primary category representing a group of species. Mayr (1942) defines it as ‘a systematic unit including one species or a group of species of presumably common phylogenetic origin, separated by a decided gap from other similar groups’. It is obligatory that every species be placed in a genus and the name of the genus (always written in italics and with a capital letter) constitutes the first word of the scientific name of a species. If there is only one species in a genus, the latter is monotypic, but if there are two or more species these are said to be congeneric and the genus polytypic.
SPECIES is the category on which present-day classification is based. It
is regarded as a natural entity, whereas classification in all other categories,
lower and higher, is subjective. Mayr (1940) defines species as ‘groups
of actually or potentially interbreeding natural populations, which are
reproductively isolated from other such groups’. Amando (1970) has
rephrased the definition as follows: ‘A species is a freely interbreeding
population whose members do not interbreed with those of other populations’.
In other words if a population of birds is breeding in a certain area in
the company of another population and the members of each mate only with
their own kind, then the two populations belong to separate species. For
example, suppose that somewhere in Guatemala Green Conures Aratinga holochlora
are commencing nesting activities, and that in the same area Orange-fronted
Conures Aratinga canicularis are also breeding. The two kinds of parrots
always pair within their own groups and not with other members of the other
group. They are separate species. However, there are obvious similarities
between them so both are placed in the same genus. Species which are found
breeding in the same area are said to be sympatric, while those which occur
in different regions are not found together are allopatric. As we shall
see later the taxonomic treatment of allopatric populations is often subjective.
(i) Subspecies occurring within a continuous distribution are illustrated by the Blue-Bonnet parrot has a yellow vent, but in the north this is red. There is no sharp geographical line of distinction but there is a narrow intermediate zone where birds have yellow vents with variable red markings.
(ii) Subspecies separated by a barrier are illustrated by the Eclectus Parrot Eclectus roratus, a large parrot occurring in the Australasian area. In the southern Moluccas the female of the nominate subspecies (the first described) is red with mauve-blue breast and collar. On sumba, in the Lesser Sunda Islands, the female is entirely red without any mauve—blue markings. The population on Sumba Island is called an isolated subspecies, or isolate, of Electus roratus and is given a different subspecific name. The nominate subspecies then becomes Electus roratus roratus and the Sumba Island population Electus roratus cornelia.
Some doubt always exists concerning the status of isolates because one can never be certain that they would interbreed if brought together; it is a matter for taxonomic judgement. However, the prevailing practice is to emphasize affinities, and isolates are generally treated as subspecies or races of a single species. In cases where the taxonomic differences are so great as to suggest that the isolate world would not interbreed with other isolates if the separating barriers were removed, the isolated populations can be treated as species within a single subspecies.
Classification is an attempt to subject living, ever-changing organisms to a static, ‘pigeon-hole’ type arrangement, so it is inevitable that there will be shortcomings. Differences of opinions from various taxonomists and inconsistencies in systematic lists are to be expected and should not be interpreted as evidence of failure of the system. In this book I have drawn attention to different arrangements, usually whether a certain form should be a subspecies or a species whether a species belongs to one genus or to another. It must be remembered that although agreement on such matters is desirable it is not essential – more importantly is knowledge of the biological facts.
As already mentioned, Psittaciformes is a very homogeneous assemblage of forms, so differences available for separation into lower categories are minor. Systematists have always had difficulties classifying parrots and most arrangements proposed have been largely artificial, though convenient. Summing up the results from his comparative examinations of cranial osteology, Thompson (1900) remarked, ‘To discover anatomical characters such as might yield or help to yield a natural classification of the Parrots has been the desire of many ornithologists, but the search has availed little’. Berlioz (1941) has expressed similar sentiments: ‘Aucun caractere osteologique nom saurait etre envisage comme critere absolu pour un essai de groupement des Perroquets et la definition de leurs affinities respectives’ (it has not been possible to envisage any osteological character as an absolute criterion for attempting to group the Parrots and to define their respective affinities).
Salvadori (1891) used a classification based entirely on external features, and it comprised seven familles, one which, Psittacidae, was divided into six subfamilies. Thompson followed Salvadori’s classification when carrying out his osteological examinations, and although he demonstrated minor differences no major alterations were proposed. The work of these two pioneers is often criticized because empahasis was placed on what are now regarded as relatively unimportant, adaptive characters, but their classification still forms the basis for taxonomy of the Psittaciformes. Reichenow (1913) proposed a new arrangement comprising eight families and one of these, Psittacidae, was divided into three subfamilies; this was not radically different from that of Salvadori. Peres (1937) also relied strongly on Salvadori’s arrangement when compiling his Check-list, but he used only one family separated into six subfamilies.
Verheyen (1956) analysed anatomical and ecological data, both published and original, on a number of species and proposed an arrangement comprising five families, three of which were divided into three or more subfamilies. Glenny (1957) looked at patterns in the carotid artery arrangement and recognized only one family, but this he divided into nine subfamilies. A radical arrangement was proposed by Brereton (1963) who, after considering both anatomical and ethological characters, set up two superfamilies. Inconclusive results were obtained by Gysels (1964) when he subjected extracts from eye lens and muscle to electrophoresis, but there was an indication that the one family of Peters comprised a number of separate subfamilies.
A major essay on systematics of parrots was presented by Smith (1975), and for most part I concur with his findings. Smith groups the genera into a number of tribes, a proposal that I find acceptable, though I differ in the composition of those tribes and am not convinced that his grouping of tribes into four subfamilies is an accurate reflection of phylogenetic relationships. I do not claim to be a taxonomist, and I do not have ready access to large collections of specimens or anatomical material from various parts of the world, so in this book there are no taxonomic discussions on the major groupings. In some instances I have stated my opinions; for example, about whether Nymphicus is a cockatoo, and about the relationships of Lathamus, but these opinions generally are confined to species I know well in the field. The end result is that in this edition I have adopted an arrangement modified from that of Smith (see fig. 2). There is only a single family – Psittacidae, with three subfamilies – Loriinae, Cacatuinae and Psittacinae, and a number of tribes are identified within Cacatuine and Psittacinae.
The scientific name is formed by writing the names of the last three categories followed by the name of the person who described and named it, in this case Bechstein. To signify that this parrot was placed in a different genus when originally described, the author’s name is put in parentheses. Therefore, the scientific name of the Rose-ringed Parakeet from southern India is: Psittacula krameri manillensis (Bechstein).
Before ending this section on classification mention must be made of the Malloghaga, ectoparasitic lice that live amongst feathers of birds. The present distribution of the Malloghaga suggests that they become parasitic on the class Aves at an early stage in the evolution of that class and that they evolved with their hosts (Clay, 1964). This means that, generally speaking, the Mollophaga of related hosts are themselves related. Different species of birds do not normally come into contact with each other so there is little chance of interchange of lice populations, and this isolation has led to host restriction, so that in many cases a species of Mallophaga is found on only one host species or on a group of closely related host species. Each order of birds is parasitized by one or more mallophagan genera that are often peculiar to it, and the relationship between species of these genera generally reflects the relationship between host and parasite, so that information about the occurrence of Mallophaga cannot be used as an infallible guide to relationships between the hosts.
Dr L. R. Guimaraes, formerly of the Museu de Zoologia da Universidade de Sao Paulo, Brazil, examined the Mallophaga from many species of parrots, with the notable exception of Micropsittini. He provided me with an outline of patterns of the relationships found in Ischnoceran Mallophage, and some very interesting aspects are present. Mallophagan genera and their hosts are listed in Table 1, and the geographical distribution of mallophagan genera recorded from species of Psittacinae is given in Table 2.
Parrots from the New World are parasitized only ny thr genus Paragoniocotes, and it has been found on no other group of birds. This is further evidence of the Arini being well set apart from other parrots in Psittacine, a pattern emphasised by Smith (1975) when suggesting that New World parrots may be sufficiently differentiated to warrant subfamily status. The Loriinae is parasitized only by Psittaconirmus, and this genus has not been found on any other group of parrots. Three malloghagan genera have been recorded from Cacatuinae, and one of these, Psittoecus, has not been found on any other group of parrots. There are five genera recorded from Psittacinae; two occur also on Cacatuinae, one is confined to parrots from the New World, and the recently described Theresiella has been found only on Psittacella from New Guinea. The geographical distribution of mallophagan genera from Psittacine is interesting; two are widely spread throughout Africa, Madagascar, continental Asia and the Australasian region, two have been recorded only from the Australasian region, and one is restricted entirely to Central and South America.
Summing up, we find that each of the three subfamilies – Loriinae,
Cacatuinae and Psittacinae – has at least one mallophagan genus restricted
to it. In this case of Loriinae, there is only one genus and this has not
been found on any other group of parrots. Two of the three genera found
on Cacatuinae have been recorded also from Psittacinae there is a genus
confined to parrots from Central and South America, one not recorded from
the other subfamilies, another known only from Psittacella from new Guinea,
and two that have been found also on Cacatuinae.
Forshaw, Joseph M. (1989)
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