The Sunda Zebra Finch and the Australian Zebra Finch: From Fringilla to Taeniopygia
By Dirk Van den Abeele
Ornitho-Genetics VZW
De Nederlandse versie van dit artikel kan je hier lezen
In this article, we discuss why the Sunda Zebra Finch and the Australian Zebra Finch are no longer regarded today as one species with subspecies, but as two separate species. In doing so, we look at differences in distribution, appearance, behaviour, and calls, as well as the historical evolution of their scientific naming. This combination of classical taxonomy and modern genetic research reveals a surprisingly new picture of these familiar birds.
The Sunda Zebra Finch and the Australian Zebra Finch are often grouped under a single collective name: zebra finch, because technically, in aviculture, zebra finch is used as a collective term for these two species. Strange though it may seem, some aviculturists are not even aware that there are two species of zebra finch.
For me, they were the first birds I ever had in my collection. At a fairly young age, I kept pestering my parents because I wanted to get some pet birds, but they clearly were not keen on the idea. Fortunately, fate gave me a helping hand, and, at the local fair, my brother and I won a pair of zebra finches. Yes, that is unthinkable now, but back then it still happened. We were even given the choice between goldfish and birds, but our decision was made quickly, and we went for the birds. Whether they were Sunda Zebra Finches or Australian Zebra Finches, I do not know. What is certain is that these birds were the reason for my first aviary in the garden, and thus the beginning of my adventure in aviculture.
The zebra finch is a well-known species worldwide within aviculture. Although numerous colour mutations occur, the available information about them is still often based on practical experience. In many cases, a clear scientific foundation is lacking, which means that descriptions and theories can differ from one another.
Outside aviculture as well, the zebra finch is of great importance to researchers. The fact that these birds reproduce relatively young and easily has undoubtedly contributed to that. One of the most important researchers in this field is the Australian ornithologist Richard Alexis Zann (1944–2009). He devoted a large part of his life to the study of Australian estrildid finches, and in particular to the zebra finch. In 1996 he published The Zebra Finch: A Synthesis of Field and Laboratory Studies [1]. That book was the result of years of observations of the zebra finch, both in its natural habitat and in aviculture. It provided valuable insights into the behaviour and ecology of these birds in the wild.
Australian Zebra Finch
This is the species we know best in aviculture and the one that serves as the model for the majority of scientific studies. It occurs over approximately 75% of the Australian mainland, with a clear preference for the dry (arid) and semi-arid interior. According to the IUCN Red List, the species has the status ‘Least Concern’ in the wild, that is, it is not threatened [2]. Its habitat consists of open grasslands with scattered shrubs and trees (such as acacias) that serve as nesting sites and shelter. A crucial factor is proximity to water; they rarely stay far from a water source. Furthermore, their diet consists of approximately 98% seeds, mainly grasses, which they forage for on the ground. During the breeding season, they sometimes supplement this with small insects, such as ants or termites, to provide the chicks with extra protein, although that share remains limited.
They are largely nomadic. This is because they usually inhabit very dry areas and are forced to follow rainfall and food sources. They are extremely social and live in colonies or flocks that may range from dozens to hundreds of birds.
The Australian Zebra Finch has no fixed breeding season but generally begins breeding only after sufficient rain has fallen and an abundance of fresh grass seed is available. We see that pattern in many other species from dry regions as well. In nature, these birds are monogamous and partners usually remain together for a long time. They rarely leave each other’s side, forage together, and build the nest jointly. They breed in loose colonies, with timing often closely matching that of neighbouring pairs [3], [4], [5].
Sunda Zebra Finch
Richard Alexis Zann describes the Sunda Zebra Finch, which he himself called the ‘Sunda Zebra Finch’, as a smaller form that differs in several respects from the Australian species. The Sunda Zebra Finch occurs on Timor and the surrounding Lesser Sunda Islands, an island group in Indonesia east of Bali and north of Australia. The archipelago comprises more than 500 islands, of which Bali, Lombok, Sumbawa, Sumba, Flores, and Timor are the largest and best known. In biogeographical terms, the Sunda Zebra Finch lives in Wallacea, a transitional region between the Asian (Sunda) and Australian (Sahul) continental plates [6].
Unlike the Australian species, the Sunda Zebra Finch lives in a more tropical, though still relatively dry, island climate. The species is found mainly in low-lying coastal areas, open savannas, grasslands, and even in cultivated landscapes such as rice fields and villages. They are primarily seed eaters, feeding mainly on grass seeds. Because of the more stable climate on the islands, their food supply is generally more predictable than in the Australian desert regions. As a result, they often remain in the same area throughout their lives. Like the Australian Zebra Finch, this species is also classified by the IUCN as not threatened in the wild [2].
Zann notes that the call (the ‘distance call’) of the Sunda Zebra Finch differs from that of the Australian species. It lacks the characteristic ‘noise element’ that is present in the Australian Zebra Finch. The call is shorter and higher-pitched. This was confirmed again by scientific research in 2019 [7]. Sunda Zebra Finches are also smaller and lighter (about 10–20%) and show finer and less conspicuous throat markings. A wild Australian Zebra Finch generally weighs between 11 and 13 grams, whereas Sunda Zebra Finches usually weigh only 8 to 9 grams. Their social behaviour in colonies is similar, although those colonies are often smaller than the large flocks in the Australian outback.
An interesting detail is that in 1990 Professor N.S. Clayton published a study in the journal Animal Behaviour on mate choice in zebra finches. Experiments in aviaries showed that both the Australian Zebra Finch and the Sunda Zebra Finch show a clear preference for partners of their own species. This distinction is presumably made on the basis of song and external features, such as body size and the breast band. In particular, the width of the black breast band in males proved to be an important visual cue. Thus, female Sunda Zebra Finches consistently chose ‘natural’ Sunda Zebra Finch males with a narrow breast band. Female Australian Zebra Finches, by contrast, were attracted by Timor males to which a broader breast band had been experimentally added, making them look more like males of their own species. The research also showed that the two species are fertile with one another. Professor Clayton, however, did not describe the appearance of the hybrid offspring, because her study was entirely focused on behaviour and on the mechanisms behind mate choice, not on genetics or the physical characteristics of the offspring [8].
Let us list the differences between the two species.
| Sunda Zebra Finch | Australian Zebra Finch | |
| Habitat | Tropical lowlands, islands (Timor and the Lesser Sunda Islands) | Arid and semi-arid regions, across Australia |
| Size | Approx. 8–10 cm (smaller/thinner) | Approx. 10–12 cm (more robust) |
| Throat markings | Finer and less conspicuous throat markings | Clear black “zebra” stripes up to the breast band |
| Call | Higher-pitched, shorter, lacking the characteristic noise element | Lower-pitched, with a characteristic noise element |
Taxonomy
In recent years, the taxonomy of zebra finches has undergone major revision. Whereas we previously spoke of one species with two subspecies, modern genetic research indicates that the differences run deeper than we thought. Where the Sunda Zebra Finch and the Australian Zebra Finch were previously regarded as two variants of the same species [Taeniopygia guttata], current taxonomy has now officially split them into two full species [9], [10]. The current taxonomy, grounded in scientific evidence, now looks as follows:
Taeniopygia Reichenbach, 1862
- Taeniopygia guttata (Vieillot) 1817 – Sunda Zebra Finch
- Taeniopygia castanotis (Gould) 1837 – Australian Zebra Finch
As often happens, not all ornithological lists have yet adopted this new classification. That sometimes causes confusion within aviculture. In this article, we explain the background to this classification. And, as you have come to expect from us, we begin with a dive into the past.
1805. Le Bengali moucheté
Anyone searching the taxonomic literature will read that the first formal scientific description dates from 1817, when the French ornithologist Louis Jean Pierre Vieillot (1748–1830) described the Sunda Zebra Finch as Fringilla guttata. He did so in the book Nouveau dictionnaire d’histoire naturelle, appliquée aux arts, à l’agriculture, à l’économie rurale et domestique, à la médecine, etc. This authoritative French encyclopaedia of natural history for its time was published in Paris between 1816 and 1819 and was compiled by several renowned scientists. Yet that was not the first description of this species.
Vieillot based himself on specimens that were probably collected during Nicolas Baudin’s expedition to Australia and Indonesia (1754–1803). It was Napoleon Bonaparte himself who, in 1800, authorised a scientific expedition to what were then called the ‘Terres Australes’. The aim was not only to map the coast of Australia and assess the extent of British influence there, but above all to study natural history. Two ships were assigned for this purpose: Le Géographe, under Baudin’s command, and Le Naturaliste, with Captain Emmanuel Hamelin. On board there was, for that time, a record number of 22 scientists, including astronomers, botanists, zoologists, and artists. That was exceptional for the period.
During this journey to ‘Australia’—then still New Holland—and the Indonesian islands, the expedition stopped on the island of Timor in 1801. That is most probably where the French first encountered the Sunda Zebra Finch. The birds were collected on site by naturalists such as Jean-Baptiste Leschenault de la Tour (1773–1826) and possibly also François Péron (1775–1810). This expedition amassed a staggering quantity of material. When the ships returned to France three years later, in 1803, they transported more than 100,000 specimens to the Muséum national d’Histoire naturelle in Paris, doubling the museum’s collection at a stroke. In this way, more than 2,500 new animal species were brought to attention. It then fell to Vieillot to catalogue them and assign them names.
Two years after this expedition, in 1805, Vieillot published his book Histoire naturelle des plus beaux oiseaux chanteurs de la zone torride (Natural history of the most beautiful songbirds of the torrid zone). This work is known for the magnificent hand-coloured engravings by Jean-Gabriel Prêtre. In that book we in fact already find the first description of the Sunda Zebra Finch, which Vieillot then called Le Bengali moucheté (the speckled Bengal finch).
Here I provide a translation of the original (French) text:
Le Bengali moucheté
This new species lives on the Moluccan islands, in India. When it is brought to Europe, it does not live long there if, during the first year, it cannot enjoy a warmth corresponding to that of our summers. It can be induced to reproduce only by keeping the temperature at 50 degrees and surrounding it with evergreen shrubbery that offers it the image of its homeland.
This bird has a beautiful red bill; the upper part of the head and neck, the back, and the wing coverts are ash-coloured; the flight feathers are brown; the cheeks are dark reddish-brown and crossed by a white stripe that continues along the sides of the throat. The throat itself is grey and, on the rear part, adorned with black crescent-shaped spots. The sides of the breast and belly are reddish and sprinkled with white speckles; the middle of the belly is white. The rump, tail feathers, and upper tail coverts are black; the latter are almost as long as the large feathers and end in white, heart-shaped spots. The legs are flesh-coloured.
The female differs from the male in that she has no reddish-brown colour on the cheeks and flanks, no black crescent-shaped spots on the front of the throat, and no white speckles on the tail coverts and on the sides of the breast. Her plumage is entirely grey, and her bill has a dark brown shadeYoung males resemble the female; but after their first moult, they become recognisable by the white stripe along the sides of the head and by the dark reddish-brown of the cheeks.
This bird was sent to me by Mr Bécœur…
Yet this text was later not accepted by taxonomists as the first official naming. The reason is simple: the French species name was not considered a valid scientific name. A scientific name for birds consists of several taxonomic components, of which the most important are the genus and the species name; these must be rendered in Latin. Probably Vieillot did not yet know this at that moment, or at least it was not yet an absolute requirement. Latin was already used in many publications, but no formal obligation yet existed.
Indeed, the first clear guidelines on this only appeared in 1842, when Hugh Strickland (1811–1853), together with the British Association for the Advancement of Science, set down new and existing rules on taxonomy in writing[11], [12]. That is one of the reasons why many early descriptions of birds were later regarded as nomenclaturally invalid. In 1892, during the second International Congress of Zoology in Moscow, it was decided to recognise the tenth edition of Systema Naturae, written by the Swedish scholar Carl Linnaeus in 1758, and its associated binomial nomenclature as the basis of zoological nomenclature and thus also of taxonomy [13]. That set the tone, and many names were adjusted. Today, it is ‘The International Commission on Zoological Nomenclature (I.C.Z.N.)’ in London that, as the official body, maintains the rules and guidelines for scientific names.
The official and extensive expedition report of the voyage, Voyage de découvertes aux terres australes, began to be published from 1807 onwards by Péron and Freycinet. François Auguste Péron (1775–1810) was one of the driving forces behind the scientific success of the expedition. He began as an assistant zoologist but grew into a central figure in reporting and in observations of animal behaviour. Louis Claude de Saulces de Freycinet (1779–1842) took part in the expedition to map the south and southwest coast of Australia. The publication therefore also included an accompanying Atlas with maps of the Australian coastline, largely produced by Freycinet. The illustrations in this work are by Charles-Alexandre Lesueur (1778–1846). They are particularly detailed and depict the animals with striking vitality. Although he came aboard as an assistant gunner, Lesueur became the expedition’s principal illustrator after the official artists had left the ships because of illness or disagreements with Baudin. The originals of these drawings are now largely housed in the Muséum d’histoire naturelle in Le Havre, Lesueur’s birthplace. Thousands of his sketches are kept there, from the smallest insects to the now-extinct dwarf emu of King Island.
One might expect the Dutch (VOC—the Dutch East India Company), who had been active in Timor and Australia for much longer, to have described this bird earlier. Although Dutch colonists undoubtedly noticed the birds—they are hard to miss—their attention in that period was focused mainly on spices, larger animals, and plants of economic value. As a result, that ‘little Sunda Zebra Finch’ probably never made it into the official Dutch logbooks.
1817. Fringilla guttata
Fortunately for Vieillot, he repeated his description in 1817 in the Nouveau Dictionnaire d’Histoire Naturelle. This extensive multi-volume work was published between 1816 and 1819. In the section on zoology and botany, we find detailed descriptions of species from around the world. Because science in that period was in rapid motion thanks to numerous expeditions, it contains many species that had only recently been discovered in America, Africa, and Australia.
In volume 12, on page 233, we find a description of the Sunda Zebra Finch. There Vieillot describes this species under the French name ‘Le Diamant moucheté’ (the speckled diamond finch), but now also gives it a Latin name: Fringilla guttata. As a result, this description does meet the taxonomic requirements and is therefore accepted as the valid nomenclatural basis for the species. Vieillot moreover explicitly states that the bird was brought back by Baudin’s expedition and that the specimen is preserved in the museum in Paris. This specimen thereby became the name-bearing type of the species, i.e. the holotype: a specimen—in this case a skin—to which taxonomists can always refer and which, in cases of doubt, serves as the standard example of the species.
What follows is a translation of the original French text:
The speckled Bengal finch, Fringilla guttata, depicted on plate 3 of Oiseaux chanteurs.
This beautiful bird from the Moluccan islands has a red bill; all the upperparts are ash-coloured; the wing flight feathers are brown; the cheeks are dark reddish-brown and are crossed by a white stripe that continues along the sides of the throat. The throat itself is grey and, on the rear part, adorned with black crescent-shaped spots. The sides of the breast and belly are reddish and sprinkled with white speckles; the middle of the belly is white. The rump and the upper tail coverts are black; the latter are almost as long as the large tail feathers and end in white, heart-shaped spots. The legs are flesh-coloured.
The female differs from the male in that she lacks the reddish-brown colour on the cheeks and flanks, the black crescent-shaped spots on the front of the throat, and the black speckles on the tail coverts and on the sides of the breast. Her plumage is entirely grey, and her bill has a dark brown shade. The male resembles the female when young; but after the first moult, he becomes recognisable by the white stripes at the sides of the head and by the dark reddish-brown of the cheeks.
In doing so, Vieillot placed these birds in the genus Fringilla. Indeed, at that time it was thought that almost all finch-like birds worldwide belonged to the genus Fringilla. The focus then was purely on bill shape. The genus Fringilla was introduced by the Swedish researcher Carl Linnaeus in 1758 in the 10th edition of his work Systema Naturae. Thus, it became Fringilla guttata, literally ‘the speckled finch’. Fringilla is the Latin name for finch [14, p. 164] and guttata stands for spotted or speckled [14, p. 181].
1837. Amadina castanotis
Only twenty years later, in 1837, the Australian species was officially described by the famous ornithologist John Gould (1804–1881). Unlike Vieillot, who worked mainly from skins, Gould had observed these birds himself in Australia. He described them as Amadina castanotis in the groundbreaking ornithological work Synopsis of the Birds of Australia and the Adjacent Islands. This book contained, among other things, 73 coloured lithographs based on drawings by his late wife Elizabeth Gould. It was the first major publication on Australian birds, with information on more than 160 species.
Here I give the English translation of the original text, which is written partly in Latin and partly in English.
AMADINA CASTANOTIS, Gould.
Male. Fig. 1.
Latin description (male): Body above ash grey-brown; wings brown; rump white; upper tail coverts black with white spots; cheeks chestnut-red, with a white line at the base of the bill; breast grey, transversely striped with black lines, with a black patch in the middle of the breast; belly white; undertail coverts ochre-yellow; flanks chestnut-brown with white spots; bill orange; legs yellowish.
Latin description (female): Bill, facial crosslines, upper tail coverts, and legs as in the male; back, ear coverts, wings, tail, and flanks grey, brown; throat and breast grey with a reddish tinge; belly yellow brown.
Measurements: Total length: 4¼ unc.; wing (ala): 2?; tail (cauda): 1½; tarsus: ¾.
MALE. Crown of the head, nape, and back brownish grey; wings brown; rump white; upper tail- coverts jet black; each feather having three large and conspicuous oval spots of white ; tail-feathers blackish brown slightly tinged with white at their tips; cheeks and ear-coverts reddish chestnut separated from the bill by a narrow transverse line of white, which white line is bounded on each side by a still finer line of black; throat and chest grey, the feathers transversely marked with fine lines of black; a small black patch on the middle of the chest; abdomen white; under tail-coverts buffy white; flanks chestnut, each feather marked near the tip with two small oval spots of white; bill orange red ; feet light yellowish flesh colour.
FEMALE. Transverse lines on the face, upper tail-coverts, and feet, as in the male; upper surface, ear-coverts, wings, tail, and flanks greyish brown; throat and chest grey slightly tinged with brown ; abdomen yellowish brown.
Amadina castanotis, Gould in Proc. of Zool. Soc., Part IV., 1836.
Habitat. Australia: locality, interior of New South Wales.
In the final lines of this article, Gould states: ‘Amadina castanotis, Gould in Proc. of Zool. Soc., Part IV., 1836’. By this he referred to the minutes of the meeting of the Zoological Society of London of 25 October 1836, where he had first presented this Australian Zebra Finch, together with nine other ‘new’ species, to the assembled researchers. A brief description had already been included there.
In the measurements, we find unc. That is an abbreviation of the Latin unciae, which in this context corresponds to the inch. Gould placed this zebra finch in the genus Amadina. That genus had been introduced in 1827 by the Briton William Swainson (1789–1855) for small finch-like species. With castanotis, Gould was referring to Greek: kastanon means chestnut and otis means ear. In Latinised form, the name therefore means ‘chestnut-brown ear’. Gould clearly treated this specimen as a separate species, distinguishing it from the Fringilla guttata described by Vieillot.
1845–1850
During the mid-19th century, it became common practice for prominent ornithologists to establish their legacy through the introduction of new genera. This led to a tangle of names that still regularly crop up in older literature. One name used by some German authors, among others, is Sporothlastes. That genus was proposed in 1847 by the German ornithologist Jean Cabanis (1816–1906). At the time, it was used within the family of waxbills (Estrildidae) for species that today are usually placed under Stagonopleura or Amadina. Nowadays, Sporothlastes is regarded as obsolete and as a nomen nudum, that is, a name that was published but is not valid because it was not formally substantiated according to the rules.
In 1850, Charles Lucien Bonaparte (1803–1857), a nephew of Napoleon Bonaparte, introduced the name Steganopleura guttata. In doing so, he placed the Sunda Zebra Finch in the genus Stagonopleura, a genus that had been introduced that same year by the German naturalist Heinrich Gottlieb Ludwig Reichenbach (1793–1879).
1862. Genus Taeniopygia
As collections in Europe grew, taxonomists realised that these zebra finches did not fit well within the existing genera. After all, they display a unique pattern of stripes, among other things on the tail and breast. Eventually it was Heinrich Gottlieb Ludwig Reichenbach himself who, in 1862, in Die Singvögel als Fortsetzung der vollständigsten Naturgeschichte, proposed the new genus Taeniopygia for the zebra finch. He saw that the banded breast and tail pattern within the waxbills was sufficiently distinctive to justify a separate genus.
The name is derived from the Greek words tainia (band, stripe) and pugios (rump, hind part), a reference to the black-and-white banded tail feathers so characteristic of both species. Reichenbach placed both the Sunda Zebra Finch and the Australian Zebra Finch in this genus as two separate species. From then on, it became Taeniopygia guttata for the Sunda Zebra Finch and Taeniopygia castanotis for the Australian Zebra Finch.
1890. Catalogue of the Birds in the British Museum
Towards the end of the 19th century, an attempt was made to place all known bird species into a logical system. The catalogue of the British Museum was then regarded as the worldwide standard. In volume 13 of this standard work, Richard Bowdler Sharpe (1847–1909), curator of the bird collection, once again arranged both zebra finches as two separate species within the same genus. In other words, in 1890 there was no doubt that the island form and the bird of the Australian mainland were separate biological entities.
1912. Mathews
Gregory Macalister Mathews (1876–1949) was an Australian amateur ornithologist and an authority on Australian birds. In his book A List of the Birds of Australia, he helped to establish the name Taeniopygia castanotis for the Australian population. Unfortunately, it did not stay that way.
Around this period, the Biological Species Concept gained influence. When two groups of birds looked very similar and could in theory interbreed, they were often regarded as subspecies. For the zebra finch, this meant that the Sunda Zebra Finch was by some reduced to Taeniopygia guttata guttata, while the Australian form was designated Taeniopygia guttata castanotis. In that context, people spoke of a ‘superspecies’ complex.
1943. Phoepila guttata
In the 1940s, efforts were made to make ornithology more orderly. The influential French American ornithologist Jean Théodore Delacour (1890–1985) thought there were too many small genera. He therefore proposed placing all ‘grassfinches’ with similar characteristics in one broader genus: Poephila. He did so in A revision of the subfamily Estrildinae. In this way, Delacour lumped together the genera Taeniopygia, Steganopleura, and Emblema.
The arguments for this classification included the following:
- Tail pattern: both the zebra finch and the ‘true’ Poephila species (such as the long-tailed finch) have striking white spots or bands on the tail feathers.
- Behaviour: they show similar nest-building behaviour and drink in a comparable way, namely by so-called ‘sucking’ drinking, which is rare in birds.
- Bill shape: the conical bills appeared, in the eyes of scientists of that time, sufficiently similar to place all species in one genus.
It then became customary to treat the zebra finch in the broad sense as Poephila guttata. For the Sunda Zebra Finch, this became Poephila guttata guttata, and for the Australian Zebra Finch Poephila guttata castanotis. That approach then remained in circulation among various taxonomists for several decades.
That view was further reinforced in 1958 in The comparative ethology of grassfinches gr(Erythrura) and mannikins (Lonchura), a work by Desmond Morris. Morris (1928–2026) was an influential British zoologist, ethologist, and author. He studied the courtship and social signals of these birds. Although he found differences, his work at the time still supported the idea that these finches were closely enough related to be placed in one larger group.
1987. Christidis
In the 1980s, DNA research made its entrance into ornithology. It slowly became clear that the zebra finch was morphologically and genetically something of an outsider. Researchers found that the skull structure and musculature of the zebra finch differed fundamentally from those of the ‘true’ Poephila species. Genetics ultimately provided the decisive argument against the Poephila hypothesis. Leslie Christidis (born 1959), an Australian researcher, used protein electrophoresis, a precursor of modern DNA sequencing, in 1987 to show that the zebra finch is much more closely related to the Gouldian Finch and the masked finch than to the Poephila group. In Phylogeny and systematics of the Australian finches (Passeriformes: Estrildidae), he therefore argued for the restoration of the genus Taeniopygia. He confirmed those findings again in 1994 [15].
2009. The genetic split
In 2009, the American researchers Christopher N. Balakrishnan and Scott V. Edwards published their article Nucleotide Variation, Linkage Disequilibrium and Founder-Facilitated Speciation in Wild Populations of the Zebra Finch. Their research suggests that the Sunda Zebra Finch and the Australian Zebra Finch diverged from each other 1.2 to 2 million years ago. The most likely explanation is that a small group of Australian Zebra Finches colonised the Lesser Sunda Islands. The genetic diversity of the Sunda Zebra Finch is considerably lower, which points to a founder effect in which only a limited number of birds founded the island population. In such small populations, natural selection can proceed relatively quickly, allowing physical traits, such as body size, to change quite rapidly on an evolutionary timescale as an adaptation to the island environment. [7].
The study shows that such colonisation can drastically alter genetic structure: genetic variation decreases and linkage disequilibrium (LD) increases. LD describes the extent to which genetic variants are inherited together, rather than being independently reshuffled by recombination; simply put, it concerns pieces of hereditary material that remain together more often than one would expect by chance. Through the combination of increased LD, genetic drift, and long-term isolation, small populations can diverge genetically more quickly from the original population. That process can contribute to the emergence of new subspecies or species and may therefore help explain the differences between the two zebra finches.
2010. Genome study
The zebra finch occupies a special place in scientific history: it was the second bird species ever, after the chicken, whose complete genome was mapped [16], [17]. This was a large-scale project to which hundreds of scientists contributed. The main aim was to understand which genes are involved in learning complex song.
Although the 2010 version was revolutionary, it still contained many ‘gaps’ in the data—comparable to a puzzle whose edge pieces are in place, but whose centre is still incomplete. In 2021, the Vertebrate Genomes Project (VGP) released a new version [18]. This one was much more accurate, because new techniques such as long-read sequencing were used, allowing longer DNA fragments to be read in a single run.
But scientists never really stop ‘mapping’ it. Since 2021, further refinements have been continuous. The most recent study included in the bibliography dates from 2025 [19]. It shows that the zebra finch genome comprises approximately 1.2 billion base pairs and is organised in a karyotype of 2n = 82 chromosomes (41 pairs), consisting of a small number of large macrochromosomes and a large number of very small microchromosomes. Remarkably, the 2021 research still assumed 80 chromosomes. The fact that 82 have now been identified once again illustrates how our knowledge evolves as analytical techniques become more refined.
2014. Vocal Communication
In his 2014 article, Claudio V. Mello explains why the zebra finch is an ideal animal model for research into vocal communication and language. Because these birds reproduce easily and sing throughout the year, scientists can study their learning processes and the associated brain circuits with great precision. That research is valuable not only for biology but also offers fundamental insights into the way the human brain processes language and how speech disorders arise. In addition, Mello describes how variations in vocalisations, such as in the Sunda Zebra Finch, can contribute to reproductive isolation: when birds no longer properly recognise one another’s calls, they will be less likely to mate [20]. The fact that the call of the Sunda Zebra Finch and the Australian Zebra Finch differs had already been noted by Alexis Zann in 1996 [1] but was later also placed in a broader neurobiological and evolutionary context.
2020. Two species
Thanks to modern techniques, today we can no longer investigate just a single gene, but analyse entire genomes. A team of researchers led by the Swedish professor Urban Olsson used this approach to fundamentally revise the phylogenetic family tree of the waxbills (Estrildidae). In this far-reaching taxonomic shift, the zebra finch plays a central role.
Based on this extensive DNA research, the study concludes that the zebra finch should no longer be regarded as a single species with subspecies, but that a split into two autonomous species better matches the evolutionary history: the Australian Zebra Finch (Taeniopygia castanotis) and the Sunda Zebra Finch (Taeniopygia guttata). Although both birds look very similar at first glance, their genetic profile shows that long-term isolation between the Australian mainland and the Lesser Sunda Islands has led to a clear evolutionary divide.
This new classification also has consequences for the genus Taeniopygia, which is now restricted to these zebra finches. The Double-barred finch, which was previously placed in the same genus as a close relative, has, on the basis of phylogenetic analysis, been returned to its own genus Stizoptera. This emphasises that, genetically speaking, the zebra finch occupies a more unique position within the Australasian bird world than was previously assumed. The study also places the species in a broader context of rapid adaptation to the dry and demanding landscapes of the Australian interior.
For both science and the enthusiast, this means that our familiar Australian Zebra Finch is once again treated as a full species in its own right, separate from the island form and more clearly delineated from other related taxa.
This scientific revision shows how modern genetics continually refines our view of biodiversity and of the complexity of seemingly simple bird species.
Let me list them briefly once again.
- Today, based on morphological, behavioural, and genetic data, the Sunda Zebra Finch and the Australian Zebra Finch are regarded as two separate species.
- Important differences include distribution, body size, calls, and several external feature
- The history of these birds shows how taxonomy continually evolves as new research methods become available.
You might think that we now have the full picture. Yet I can assure you that we are still far from finished. Science evolves constantly and compels us to keep refining existing knowledge time and again. Perhaps that is also a good lesson for aviculture.
References
[1] R. A. Zann, The Zebra Finch: A Synthesis Of Field And Laboratory Studies. Oxford University Press, 1996. doi: 10.1093/oso/9780198540793.001.0001.
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