Whydahs and Indigobirds

Class AVES Order PASSERIFORMES Suborder OSCINES Family VIDUIDAE (WHYDAHS AND INDIGOBIRDS) free text from the Handbook of the Birds of the World.

Small passerines with short, stubby bill, breeding males of most species with extensive black in plumage, some also with greatly elongated central tail feathers, females and non-breeding males mostly brownish and streaked.

10-43 cm (including elongated inner rectrices of male whydahs).

Sub-Saharan Africa.

Open country, from grassland to open woodland.

2 genera, 20 species, 28 taxa.

No species threatened; none extinct since 1600.

Systematics

The whydahs and indigobirds, together with the Cuckoo Finch (Anomalospiza imberbis), constitute the family Viduidae, a group confined to the Afrotropical Region, occurring only in the sub-Saharan part of the continent. All of the species are brood-parasitic, laying their eggs in the nests of other species; the hosts rear the young viduids along with their own young. The family consists of two genera, the monotypic Anomalospiza, with the Cuckoo Finch, and Vidua, which consists of 19 species of whydah and indigobird. The brood-parasitic Viduidae and the waxbills (Estrildidae), which are their primary host species, diverged about 20 million years ago. Several morphological characters support a close relationship between Anomalospiza and Vidua and are different from those of the weavers (Ploceidae). Most significantly, the skull, the bony palate, the horny palate and the pterylosis of Anomalospiza are much like those of Vidua and unlike those of the other Old World “finches”.

Phylogenetic relationships among the viduid species have been estimated with molecular genetics. In analyses of mitochondrial restriction sites and nucleotide sequences, the Vidua finches are a single lineage, more closely related to each other than they are to any other bird species. The indigobirds are short-tailed birds the ancestors of which had long-tailed males. Indigobirds are closely related to the Straw-tailed Whydah (Vidua fischeri) and the Shaft-tailed Whydah (Vidua regia). A second species group consists of the five paradise-whydahs: the Long-tailed (Vidua paradisaea), Broad-tailed (Vidua obtusa), Sahel (Vidua orientalis), Exclamatory (Vidua interjecta) and Togo Paradise-whydahs (Vidua togoensis). The relationships among the other whydahs are less well known. Different models indicate uncertainty over whether the basal branch of the lineage consists of the paradise-whydahs, the Steel-blue Whydah (Vidua hypocherina) or the Pin-tailed Whydah (Vidua macroura). Certain species groups have been assigned distinct genera, with the indigobirds in Hypochera, the Shaft-tailed and Straw-tailed Whydahs in Tetraenura, and the paradise-whydahs in Steganura. Because the relationships among these species groups are uncertain, however, recognition of these genera would be problematic. A broad genus Vidua is supported by the morphological and genetic data.

Vidua species differ from one another in size, in breeding plumage and colour, and in the songs used in courtship and mate choice. The long-tailed whydahs are distinctive in breeding plumage. In contrast, the indigobirds are very similar to one another in appearance, and the true taxonomic status of the various “cryptic species” formerly included within an expanded V. chalybeata was resolved only when their songs were discovered: each mimics the song of its host species. Before that time, H. Lynes commented, in 1924, that “One wonders whether the highest education will ever enable them to be distinguished apart in the field, or whether one will have to give it up because breeding males all look ‘just indigo’ and all others ‘just like sparrows [Passeridae]’ with striped faces”. Early studies of indigobirds were based on museum specimens, and authors in the 1960s estimated that there were from one to eight species. The males have glossy black breeding plumage and no ornamental patches or plumes; they differ from one another in average size, in brightness and colour of the plumage gloss, in the colour of the flight-feathers, which are black, dark brown or pale brown, and, in some cases, in the colour of the bill and feet. The females differ in size, plumage, and bill and foot colours. Field observations and tape recordings have shown that males having different plumages mimic the songs of different estrildid finches, which are their host species (see Voice). The present understanding is that there are ten indigobird species. The mouths of begging nestlings have distinctive colours and patterns and, in some cases, these mimic the mouths of their host species’ nestlings.

Mitochondrial and microsatellite genetic markers are shared among the various indigobird species. These shared genes may perhaps be traceable to a recent common ancestor, with gene lineages that have not been sorted through time owing to a time lag between speciation of the birds and reciprocal monophyly of the genes. Alternatively, the shared genes may indicate hybridization between species, or, indeed, both processes may occur. In addition, these genetic markers indicate two geographical sets of species. The indigobird species in West Africa are each other’s closest relatives, and they share mitochondrial genes. Similarly, the indigobirds in East Africa and southern Africa are each other’s relatives and, again, they share mitochondrial genes with each other. The speciation of these indigobirds is recent, the southern African species having diverged a few thousand years ago as calculated from the frequencies of their mitochondrial morphs, and approximately the same time period applies to the West African species.

The five paradise-whydahs were once considered conspecific under the name V. paradisaea. Of the currently recognized species, two, the Long-tailed and Sahel Paradise-whydahs, are song mimics and brood parasites of the Melba Finch (Pytilia melba), but mitochondrial restriction-fragment lengths and nucleotide sequences indicate that these two whydahs are not each other’s closest relative. Instead, the Long-tailed Paradise-whydah and the Broad-tailed Paradise-whydah are sister-species, as are the Sahel, Exclamatory and Togo Paradise-whydahs. No interbreeding between the Long-tailed and Broad-tailed Paradise-whydahs has been observed in regions where the two co-occur, as they do in many localities in Zimbabwe, Zambia, Malawi and Tanzania.

In 1758, in his description of “Emberiza paradisaea”, Linnaeus noted the long acuminate tail with the innermost rectrices not so long as the next pair, and this clearly represents the Long-tailed Paradise-whydah of eastern and southern Africa. In addition to his description, Linnaeus listed the seventeenth-century woodcut by U. Aldrovandi, the “Passer indicus” of F. Willughby in 1676, and the “red-breasted long-tailed finch” described by G. Edwards in 1747. Aldrovandi’s paradise-whydah is the bird now known as V. orientalis aucupum. J. Ligozzi’s painting of this bird shows it as having a reddish nape of the same colour as the breast, as in Aldrovandi’s descriptions, and a tail lacking a tapered tip. Willughby described Aldrovandi’s two whydahs, but Willughby’s plate xlv shows “Passer Indicus macrouros rostro miniaceo” V. macroura, which was illustrated and described by Aldrovandi as “de passere indico macrouro rostro miniaceo”, and not as “Passer Indicus macrouros alius” the paradise-whydah, which was not illustrated in Willughby. Finally, Edwards, in his 1747 A Natural History of Birds, described and had a colour plate of an aviary bird from Angola, V. paradisaea, which fits the description given in Linnaeus. Although Linnaeus’s citations suggest a composite whydah, his description of V. paradisaea is clearly referable to the paradise-whydah with a long, tapering tail as illustrated by Edwards. Later, in 1766, Linnaeus designated the type locality of paradisaea as “Africae regno Angolensi”, or modern-day Angola.

As with the paradise-whydahs, the indigobirds were once, as intimated in the preceding paragraphs, considered all to be conspecific. The ten species now recognized differ in male breeding plumage, in bill and foot colour, and usually in song, and in some cases in nestling mouth pattern and colours. The adults differ also in average wing length, notwithstanding some overlap in measurements between certain species. As many as three or four species are sympatric in some localities, but with no morphological evidence of interbreeding. Although earlier authors considered the red-billed subspecies amauropteryx of the Village Indigobird (Vidua chalybeata) to be a distinct species, red-billed and white-billed individuals occur in mixed populations, have the same songs and compete for the same call-sites and breeding females in south-west Zambia, north-west Zimbabwe and north Botswana.

Speciation in the genus Vidua has occurred with a shift of host species. This is remarkable for the importance of a behavioural switch as a defining event in the origin of new species, rather than simply a geographical separation of populations. At one time, it was thought that speciation of the brood-parasitic finches was linked with speciation of their host taxa. In this model of co-speciation, Vidua were tied forever to their hosts, in so far as only the usual host species would rear the young, owing to the importance of chick mouth mimicry in the parental care by the host. A gradual change in nestling mouths of host species could be tracked by the brood parasites, in a one-to-one pattern of gradual co-evolution. The idea was tested by genetic comparisons of Vidua and their hosts. When the model of co-speciation was compared with a model of host-switching or the colonization of a new host, the species phylogeny of Vidua did not parallel the phylogeny of their hosts. From that result, the idea of co-speciation can be rejected.

Field observations and breeding experiments point to host shift and song mimicry as the drivers of speciation through sexual selection. In the field, a few odd males mimic the songs of the “wrong” host species, and these bear witness to the success of the occasional host switch by females whose offspring were reared by an alternative host species and had learnt its songs and calls. In one case in the Transvaal lowveldt in South Africa, a male Village Indigobird mimicked the songs and calls of Jameson’s Firefinch (Lagonosticta rhodopareia), the host of the Purple Indigobird (Vidua purpurascens), rather than those of its own usual host, the Red-billed Firefinch (Lagonosticta senegala). A few male indigobirds, just four out of 484, whose songs were recorded in localities where two or more indigobird species occur together gave the mimicked songs of an alternative host species. The Village Indigobird is the most abundant viduid in southern and south-central Africa, and the number of “misimprinted” individuals of this species reflects their abundance.

In the field, females were identified as they visited the singing males. In southern Africa, female Village Indigobirds have a red bill and feet like those of the males, and female Purple Indigobirds have a whitish bill and feet like males of that species. Nearly all females visit males with the matching bill and foot colours. Females that visit males with odd songs are females of the other indigobird species. In one such case, a female Purple Indigobird in the Transvaal was attracted to the male Village Indigobird that mimicked songs of Jameson’s Firefinch, just as females of this indigobird normally are attracted to male Purple Indigobirds that mimic Jameson’s Firefinch. Females appear be attracted more to song mimicry of their host species than to the plumage and bill and foot colours of the singing males, and it is likely that the Transvaal female was reared by the alternative host species.

Host switches occur also at the local population scale of “song races” or “host races”. On the upper Zambezi River, some Village Indigobirds mimic songs and parasitize nests of their usual host species, the Red-billed Firefinch; other indigobirds mimic songs of the Brown Firefinch (Lagonosticta nitidula). These two song races are the same in morphology and in mitochondrial and microsatellite genetics. The local population of those mimicking the Brown Firefinch was derived from Red-billed Firefinch song mimics, which are widespread; the nestlings of Brown Firefinch mimics have mouth markings like those of nestling Red-billed Firefinches, not like those of nestling Brown Firefinches. The two song races are the result of a recent switch to a new host species at a population level, with no geographical separation between them. Colonization of the host Brown Firefinch involved several female indigobirds, as determined by the diversity of the maternally inherited mtDNA.

Over a wider geographical region, two or more song races of Cameroon Indigobirds live together in a mixed population in West Africa. In Cameroon some males copy songs of the African Firefinch (Lagonosticta rubricata) and other males mimic the Black-bellied Firefinch (Lagonosticta rara), and in south-east Nigeria some males mimic the Brown Twinspot (Clytospiza monteiri). In the Fouta Djalon uplands of Guinea and Sierra Leone, and in Guinea-Bissau, males mimic the African Firefinch, the Black-bellied Firefinch or Dybowski’s Twinspot (Euschistospiza dybowskii). These song races do not differ in plumage colour or in size.

Local populations that mimic the songs of different host species are not necessarily themselves of different species, at least where the indigobirds concerned do not differ in morphology. Further, as has been revealed in several studies, populations of Village Indigobirds that mimic the songs of different firefinch species are not genetically distinct in mitochondrial or microsatellite markers. In Cameroon, in playback tests where song races of the Cameroon Indigobird (Vidua camerunensis) occur together, a male responded more strongly to songs of his own species and his own song race than he did to songs of males with other mimicry songs. This aggressive response indicates that song may function to counter the reproductive challenge of other males. When extrapolating from this to females, which do not respond to song playback in the field, the response suggests a degree of sexual isolation between song races.

The process of host-switching in times past has been reproduced among individuals breeding in the aviary. In these experiments, the male Village Indigobirds reared by a novel host species imitate the songs and calls of their new host, and not those of their normal host species. Females reared by the novel host are attracted to male songs that mimic those of this novel host, and females lay their eggs in the nests of this novel species, rather than in the nests of the normal host. Finally, estrildid finches rear the chicks that hatch in their nest, irrespective of whether the nestlings are of their own species, of another estrildid species or of an indigobird. In these experiments, some nestlings were reared in mixed broods, whether or not the young had matching mouth pattern and colours. Food was never in short supply, and in these conditions there was no sign of discrimination against any nestlings in terms of parental care. The change in behaviour would need to persist over many generations before genetic differentiation had progressed to a stage at which song populations could be recognized as new species.

Males of other song races also mimic begging calls of the other host species, and so do males of other indigobird species: all give a song containing the begging call of their host species, as well as a begging call like that of the young indigobird. Taken together, field observations indicate that females sometimes have success when they lay in the nests of an alternative host species, and the new host rears the young indigobirds, which become imprinted on the new host species and thus establish a new brood-parasite-host association. The begging calls have not diverged to mimic the nestling calls of most host species, even though the mouth colours and pattern of the begging young of several indigobird species mimic those of the nestlings of their host species.

A switch from one host species to another has been a critical process in speciation, and this host switch occurs in areas of sympatry of the host species, yet geographical isolation may also be involved in the differentiation of indigobird species. Village Indigobirds differ in plumage and bill colour across Africa. Those in Senegal have the male breeding plumage green to blue, but in most of West Africa the plumage is bright blue; in Ethiopia it is purple, and in East and southern Africa it is dull blue to steely greenish-blue. Wing colour is black in West Africa, and dark brown in eastern and southern Africa. Finally, the bill is white in most of Africa, but red in southern Africa. These populations are described as subspecies, and their variation points to the evolution of geographical differentiation in this species.

Although the birds switched from host to host, they also underwent differentiation by distance and geographical isolation. Within a geographical region, the indigobird species are more similar to each other in body size and in mitochondrial DNA (mtDNA) than they are to the species in another region. In one case, the birds that mimic songs of the African Firefinch in West Africa are more similar in morphology and mitochondrial genetics to song mimics of other firefinch species in West Africa than they are to their counterparts with mimic songs of the African Firefinch in southern Africa. In another case, the indigobird song mimics of the Red-billed Firefinch in West Africa are more similar in mtDNA and size to other West African indigobird species than to the eastern and southern African mimics of this firefinch. In Kenya, the population is a mix of West and East African mtDNA; in this population, the plumage is morphologically uniform, being intermediate between those of the subspecies to the west, the north-east and the south, and this intermediacy in plumage, as well as the mimetic songs used in mate choice, are reasons for treating the various populations as representatives of a single species, the Village Indigobird. The few individuals in East Africa having West African mitochondria may be indicative of dispersal between regions, or may represent a genetic morph that was retained when birds in one of these regions underwent a major genetic change. As suggested by N. K. Klein and R. B. Payne in 1998 and by M. D. Sorenson and colleagues in 2003, the overlap in mtDNA between indigobird species within a region may result from a time lag in lineage-sorting of gene morphs that were present in ancestral populations, and from hybridization between the species.

Hybridization between indigobird species is uncommon. The males differ in breeding plumage, and only very rarely are individuals in intermediate plumage seen. The competitive interspecific interactions of males at a call-site and the attraction of females to “song-misimprinted” males, as well as the misimprinting of females reared by an alternative host species, may result in interspecific hybridization. The low incidence of misimprinted singing males, less than 1% in one study, does, however, indicate a strongly assortative mating system. A few males have mitochondrial genes unlike those of others of their species, and like those of another local species. A male Quailfinch Indigobird (Vidua nigeriae) at Garoua, in Cameroon, had song mimicry of a Quailfinch (Ortygospiza atricollis) and the mtDNA of a Village Indigobird. Introgression of a Village Indigobird gene into the Quailfinch Indigobird population may be due to a Village Indigobird maternal ancestor that was reared by and imprinted on a Quailfinch, the usual host of the Quailfinch Indigobird, and then joined the population of indigobirds that parasitize the Quailfinch. This is much as in the case of hybridization by an indigobird with a whydah, described below.

In the field, a few hybrids between species groups are known. The best-documented hybrids are two indigobird x paradise-whydahs in Zambia, where males in breeding plumage appeared at the same site and chased each other. Their plumage and their display behaviour were intermediate between those of indigobirds and those of the Long-tailed Paradise-whydah, and their song mimicked the songs and calls of the Melba Finch, the normal host species of the whydah. Mitochondrial DNA of the hybrid male was like that of the indigobirds, which parasitize and mimic the songs of firefinches. The individual life history of one of these hybrid viduids was recovered from its song mimicry and its mitochondria, as Vidua species learn the songs from their foster parents and the birds inherit their mitochondrial genes from their mother. In the first generation, a female indigobird laid an egg in a Melba Finch nest. The Melba Finch reared the young indigobird, a female, and the latter became imprinted upon the song of her foster parent. As a breeding adult, she was attracted to and mated with a male paradise-whydah mimic of the Melba Finch. She was then attracted to nesting Melba Finches and laid her eggs in their nest, and her hybrid young were reared by the Melba Finches. The two male whydahs, hybrids in the third generation of this family history, mimicked the songs of the Melba Finch.

Other Vidua hybrids seen or captured in the field or bred in captivity are thought to be crosses between indigobirds and Long-tailed Paradise-whydahs, between an indigobird and a Shaft-tailed Whydah, and between a Shaft-tailed Whydah and a Long-tailed Paradise-whydah. Other long-tailed, black individuals are thought to be Pin-tailed Whydah x indigobird hybrids; it would be worth testing museum specimens of long-tailed black whydahs for genes of these species. A few hybrids have been described as distinct genera and species. Two of these whydahs, Microchera haagneri, described in 1926, and Prosteganura haagneri okadai, named in 1930, had the central two pairs of tail feathers twisted by 90 degrees, and the innermost pair enveloped by the next pair; the pointed feather tips suggested the Long-tailed Paradise-whydah as one parent species, and the all-black plumage indicated an indigobird as the other parent. Hybrid black whydahs without a flag at the end of the tail were bred in captivity from the Village Indigobird and a cross between the Dusky Indigobird (Vidua funerea) and the Shaft-tailed Whydah. In Botswana, another black whydah had songs that mimicked the Violet-eared Waxbill (Granatina granatina), the host of the Shaft-tailed Whydah. In some cases, it has been thought that a black viduid with a long tail may have been simply an indigobird with elongated tail feathers. In most instances of hybridization, the causes appear to involve the act of laying in the wrong nest, misimprinting, and female attraction to host-mimicry songs by a male that is usually reared by her own host species.

Morphological Aspects

Viduids are small songbirds with a short, stubby bill. The species are similar in body size, being approximately 10-20 cm long, excluding the long ornamental central tail feathers of male whydahs, and weighing 11-24 g. All are sexually dimorphic. The male Cuckoo Finch is greenish and yellow. Males of the whydahs and indigobirds have extensive black in the breeding plumage, and whydah males have the inner two pairs of rectrices elongated, in contrast to the additional elongated rectrices of the long-tailed male widowbirds in the ploceid genus Euplectes. Female viduids are streaked brown.

Whydahs and indigobirds undergo a seasonal change in plumage through two annual moults. The body plumage is moulted twice each year, the wing once, and the tail once except for the central feathers, which are replaced twice a year in both males and females, this tail-moult pattern applying even to the short-tailed indigobirds. Indigobirds sometimes grow the two central feather pairs longer, by 2-10 mm, and more pointed than the outer four pairs. The double annual moult of the inner tail feathers and their occasional elongation are traits retained by the short-tailed indigobirds in their evolutionary derivation from long-tailed whydahs.

Cuckoo Finches change their appearance with the season as a result of feather abrasion. The male has a dark-streaked greenish back in the non-breeding season, but this is transformed to yellow upperparts and underparts in the breeding season. The dark feather tips and edges wear away to reveal the brighter yellow feather webs and the feathers become more pointed in shape, the change in plumage being acquired by wear, unlike the situation with Vidua and the Euplectes widowbirds, in which the change is brought about by moult. Female Cuckoo Finches are streaky brown above and whitish below, similar in appearance to females or non-breeding males of Euplectes, especially the short-tailed red bishops, namely the Southern Red (Euplectes orix), Northern Red (Euplectes franciscanus) and Black-winged Bishops (Euplectes hordeaceus).

The wing has a very small outermost, tenth, primary, shorter than the outer primary covert, so that no free tenth primary is apparent. This small outer primary is not unique to the viduids, as all songbirds have ten primary feathers, and the outer primary is small and well concealed below the outer covert in certain other songbird clades, including ploceids (Quelea), canaries (Serinus) and the so-called “New World nine-primaried oscines”, the latter including, among others, the families Parulidae, Thraupidae, Emberizidae and Icteridae.

Several characters of the feather tracts, or pterylosis, are common to both Vidua and Anomalospiza, and they appear to be derived within the Viduidae, or they occur within Viduidae and Estrildidae and not in the ploceid finches. These features are as follows: two rows of upper greater secondary coverts; eight upper median secondary coverts; four upper tertiary coverts; nine under greater primary coverts; a single row of ocular feathers; eight longitudinal rows of feathers on the crown; and three rictal bristles.

The skull undergoes delayed development. The frontal region of adult Vidua has a single clear layer of bone on each side of the dorsal mid-line; the clear region contrasts with the spotted appearance of the skull of other songbirds, in which two layers of bone are joined by columns and the layers are otherwise separated by a layer of air, the mature skull being pneumatized or “ossified”. Nearly all adults have an incompletely pneumatized skull. In yearling indigobirds the skull is pneumatized by about half, individuals two years old and older have the skull more than 70% pneumatized, and fewer than 5% of all birds have a fully pneumatized skull. Cuckoo Finch adults also have an incompletely pneumatized skull.

Unique skeletal features of Anomalospiza, the Cuckoo Finch, include the bill, the mouth and the palate. The bill is short and stubby, with the outline straight. The jaw is bent downwards at the frontonasal-maxillary hinge at an angle of about 110 degrees in relation to the jugal. Inside the mouth, a thick lateral surface is formed by the edge of the maxilla and a broad ventral protuberance that articulates with the jugal bone. This complex forms a crushing surface. The lower mandible of all of the viduids has a thick, flat rostral flange that is expanded ventrally at its posterior margin.

The thick bill of Anomalospiza exhibits several features that suggest a common ancestry with Vidua and others that emphasize its uniqueness. The jugal bone has a laterally compressed expansion and a ventral protuberance. The palatine has a caudal angle narrower and smaller than that found in the larger Vidua species. The vomer in Anomalospiza has a deep curling concavity matched to a lesser degree in Vidua. The pterygoid is broadly flattened, the rostral pes is expanded, and the pterygoid has a broad lateral ridge that is rotated ventrally by nearly 80 degrees, as in the Cockatiel (Nymphicus hollandicus), a member of the cockatoo family (Cacatuidae), rather than narrowly flattened, as in the Straw-tailed Whydah; the whydahs also have a ventrally rotated pterygoid. The pterygoid of Anomalospiza and Vidua is distinctive, and it differs from that of other thick-billed finch-type species such as the estrildid Black-bellied Seedcracker (Pyrenestes ostrinus), the ploceid Thick-billed Weaver (Amblyospiza albifrons) and the cardueline Hawfinch (Coccothraustes coccothraustes). The horny palate of Anomalospiza and Vidua has large depressions, or pits, near the posterior margin, one on each side of the mid-line. In Vidua, a median ridge is present on the palate. Anomalospiza lacks this ridge, and has the horny palate greatly thickened. The thick maxilla reduces the buccal cavity by more than half, and leaves a narrow medial groove into which the tongue or a seed can fit. The pits displace the lateral ridges of the palate, in contrast to the palatal condition of the ploceid finches. The medial sides of the lower jaw are dilated inwards to form two horny pads that occlude the palate pits, or fossae, when the bill is closed. The bird has a remarkably forceful bite. These structures of Anomalospiza, namely the shape of the horny palate and the thick, internally flattened lower mandible, function in breaking and crushing hard seeds. The Cuckoo Finch’s crop contains crushed seeds, not intact, hulled ones as do those of the whydahs and indigobirds.

In the postcranial skeleton, Anomalospiza has a sternum with a spina interna dorsal to the sulcus carinae, its base formed so that the internal corner of each coracoid fits into a small socket, rather than in a groove. This is much as the arrangement in the ploceid buffalo-weavers in the genera Bubalornis and Dinemellia, the sternum of which has a large spina interna and the spina externa fused anteriorly into a lateral bifid tip.

The breeding plumage of male indigobirds is black with a gloss of green, blue or purple, while that of male whydahs is black with a pattern of white, yellow, buff or reddish. Females of both groups are streaky brown and black, several having prominent stripes on the head. Non-breeding males are generally similar to the females, but the dark brown or black streaks and other marks are bolder than they are on the latter. Juveniles are dull, in some species indistinctly streaked above, and in others, such as the paradise-whydahs, unstreaked uniform grey. The plumage of juvenile paradise-whydahs is like that of the juveniles of their hosts, but without a red rump.

In the case of indigobird males, the colour of the plumage gloss is characteristic of some species. Plumage colour is difficult to determine in the field; the less glossy males can look greenish at dawn, their appearance changing through blue to nearly purple at mid-day with an overhead sun. The flight-feathers and the tail are brown or dull black with the exception of the three innermost secondaries, which are glossy black, like the breeding plumage. The tail feathers are short and spread horizontally, as in females.

Male whydahs in breeding plumage have elongated tail feathers, the two inner pairs of rectrices being several times the length of the body. These feathers are twisted 90 degrees sideways, with the inner web directed upwards, the rachis in a lateral position, and the outer web twisted downwards and inwards. These feathers are concave on the medial surface. In the Shaft-tailed Whydah, the end of each of the four central rectrices, pairs T1 and T2, is flared in a “flag” up to 6 mm broad, most of the rest of the feather having just a narrow vane 1 mm wide on each side of the rachis. The central rectrices of the breeding male Straw-tailed Whydah are narrow, just 1-2 mm broad, from the base to the tip, the narrow vanes projecting from the stiff yellow rachis. The Steel-blue and Pin-tailed Whydahs have the four central rectrices 4-6 mm broad throughout their length. The males of these four whydah species display in a short flight from a perch or the ground, the tail flopping up and down in a jerky motion.

Tail-feather structure reaches its most remarkable extreme in the breeding male Long-tailed Paradise-whydah. Each of the central pair of rectrices, T1, is long, broad, and held vertically, the “inner” or medial web in a dorsal position and the “lateral” web in a ventral position. The adjacent rectrices on each side, T2, are much longer, broad, and rotated or twisted, and they fold around the central rectrices; as with the latter, the inner webs turn 90 degrees dorsally and the outer ones turn 90 degrees ventrally. The webs of T1 are wave-like, the wave “crests” at nearly right angles to the feather shaft, providing structural support in flight display. Both T1 and T2 have a long filament composed of interlocking barbs that hold it together. That of T1 extends from the tip of the feather; the T2 filament develops from the base of the feather, much like an aftershaft, and its barbs and hooks zip into the ventral edge of the T2 web. The filament attaches to the web near the feather base; in the case of rectrix T2, the long, loose filament extends 200 mm or more, almost to the tip of the feather. The filament of T2 is lost after a few weeks, whereas that of T1 becomes abraded and loses its connection to the distal edge of the web of T2 as the breeding season progresses. The longest tail feathers, T2, bow outwards and conceal the inner T1 along the length of the tail from below; the upper edges of T1 often project above the edges of T2. In flight display, the male lifts the central feather pair to a vertical position while the adjacent T2 trail behind. In courtship display from a perch (see Breeding), the male lifts the long central pair of rectrices free of the enveloping sheath in a lateral posture that exaggerates his size and shape.

Habitat

Viduid finches live in grassland, savanna and open woodland, and are often found in bushed grassland around cultivation. Pin-tailed Whydahs inhabit wet meadows, marshes, and brushy and grassy woodlands near water, whereas paradise-whydahs are common in places far from any surface water. Most of the whydahs occur in areas having an annual rainfall of less than 1000 mm. The Pin-tailed Whydah and the indigobirds will also colonize recently cleared, once forested areas, including places in south-eastern Nigeria with an annual rainfall exceeding 2000 mm.

The Village Indigobird is commonly found in open grassy woodland and along rivercourses, even in desert regions along the River Nile and the River Niger, and near human habitations where surface water is available. The indigobirds do well in weedy cultivated areas with cotton (Gossypium), maize (Zea mays), millet (Poaceae) and manioc (Manihot esculenta), in regions where their estrildid host species, particularly the firefinches (Lagonosticta), are common. Much like their estrildid hosts, the whydahs and the indigobirds are common in the annual grasses growing around lush latrine areas near towns and villages.

Cuckoo Finches live in grassland, shrubby woodland, and grassy marshes and swamps. Unlike some of their relatives in the present family, however, they are not associated with human activities.

General Habits

The members of this family are most conspicuous during the breeding season, when male whydahs and indigobirds sing and display on their breeding territories. Male indigobirds defend their song-perch territories against males of their own species, and are also interspecifically territorial. Singing males are well separated from males of other indigobird species, the inter-male distances being much as those between males of their own species. Males of species with different local song races also space themselves as far apart as do males of the same song race. This has been found for Village Indigobird song races imprinted on, respectively, the Red-billed Firefinch and the Brown Firefinch, and for three song races of the Cameroon Indigobird, those mimicking the Black-bellied Firefinch, those imitating the African Firefinch and those copying Dybowskiçs Twinspot. The singing males chase intruding conspecific males or males of other indigobird species which approach near their call-site. Moreover, when a male disappears from his call-site, another species sometimes replaces him. In playback experiments, a singing male responds to the non-mimetic song themes more strongly than it does to mimetic song themes, and to song mimicry like his own more than to mimicry of other host species. Even so, he responds to songs of other species, and songs of a Village Indigobird have been used in playback to attract and capture other indigobird species.

Viduids occur in flocks at any time of the year, gathering together in the evening, and they often roost in flocks both in the breeding and in non-breeding seasons. Sometimes several species will flock and roost together at night in leafy trees. When gathered together, birds will occasionally produce a harsh “chut” or short chatter; they do not give song mimicry at their roosting assemblages. It is uncertain whether the actively breeding males join in these roosting flocks or roost alone, but at the end of the breeding season, and still in breeding plumage, they certainly feed together and flock for the evening roost along with the moulting males, as well as the females and juveniles. Cuckoo Finches have not been observed closely through the day, but the breeding females at all stages of their laying cycle spend much of their time in flocks; males tend to occur alone on song territories, where they are well-spaced from other males, but they also occur in flocks throughout much of the day.

Daily activity begins shortly after sunrise. The indigobirds spend the first half-hour or so feeding and drinking, after which the males take their places at their call-sites, where they sing. Some males may remain on their song perches for a full hour, but more often they take a few minutes off each hour, to feed or drink nearby, before returning. Females are less conspicuous and are perhaps most often observed when visiting a male and feeding with him near his display area. Males that have been successful in attracting a female to their sites in the previous week or so may sing throughout the day until as late as a half hour before sunset, but most males leave the call-site a few hours after they first appear in the morning. Both males and females often feed with other small finches including their estrildid host species. Pin-tailed Whydahs and most of the other long-tailed whydahs appear to start their day at much the same time as the indigobirds. Male Long-tailed Paradise-whydahs feed early and spend about an hour in the late morning and again in mid-afternoon devoted to breeding display, alternately singing from a tree and flying over their territories. The other paradise-whydahs are sometimes seen in display flight, except Broad-tailed Paradise-whydahs, which do not appear to have display flights. Female whydahs are usually seen feeding alone or near a male. Viduids also spend about half an hour feeding intensively before they fly to roost at night.

In contrast to most of the estrildid finches, viduids do not spend time with their bodies in contact during daytime behaviour or while roosting at night, and they do not allopreen, even between mates or between fledged juveniles. Their comfort or maintenance behaviour includes preening the body plumage with the bill and feet, scratching the head, fluffing the plumage, and wiping the bill on a branch. During the breeding season, male indigobirds often spend several minutes each hour on their call-sites preening themselves; they give song mimicry of their host species more often when preening and fluffing, apparently feeling at ease. Bill wiping is less clearly a movement made in connection with body maintenance, as it also occurs when an intruding male is in the call-tree, or when a male returns to his call-site after chasing a rival male.

When a flying raptor passes near the call-site, the male often stops singing, and when the raptor is within about 10 m of the site, he darts into a leafy bush and remains quiet and out of sight for a minute or two. While he is on the perch he sometimes gives a short “chut” or chatter, but he does not chase or mob the raptor. When a snake is near the call-site, the male and sometimes the female appear near the snake along with other small finches, such as Blue Waxbills (Uraeginthus angolensis), which mob and give alarm calls, but the viduids do not give alarm calls in response to the snake, nor do they take an active part in the mobbing. Terrestrial mammals such as the common dwarf mongoose (Helogale parvula) and Egyptian mongoose (Herpestes ichneumon) are generally ignored, and a male will continue to sing while the predator is on the ground nearby. Females sometimes even visit a singing male when a person is within 10 m of the call-site.

Voice

In most Vidua species, each male has two sets of song themes. One set mimics the whistled songs and social calls of the host adults, and the begging calls of the latter’s nestlings and fledglings. The other songs are harsh and obtrusive and do not mimic those of the host species. Together, the two sets comprise up to 24 distinct song themes.

This is typified by the Village Indigobird. The male of this species has eight song themes which imitate the songs and calls of the host species, the Red-billed Firefinch. Three of these mimic songs of the male firefinch; the remaining five are the begging call of the young firefinches, and the social contact calls and alarm calls of the adult firefinch. In addition to mimicry of song themes, a male has 16 kinds of chatter and song themes that are unlike any vocalizations of the host species. Certain songs are given in special social contexts. First, the male has a slow harsh chatter, “cha cha cha”, and a rapid harsh chatter, “chchchch”; he gives slow chatters while perched and when chasing another male. The male gives two other song themes when a female flies to his call-site: he utters a rapid chatter, and then, as she perches, he gives a slow chatter and then a rapid chatter and a brassy flourish. Two other songs are given during mutual chases with other males, and one of these initiates the long series of song bouts. One song theme is the begging call of the nestling and fledgling indigobird, which differs from the begging call of the nestling Red-billed Firefinch host.

In a song bout, the male Village Indigobird performs much of his song repertoire in a predictable series. The first song theme, a non-mimetic one, is often repeated several times; the other themes are repeated once or twice or are followed by a certain other one. When a male gives one theme, the next themes are somewhat predictable; alternatively, he pauses and repeats the series from the beginning, rather than running through his full repertoire. Mimetic song themes are given in a long sequence of a bout, in their own standard sequence, and a male sometimes gives mimetic begging calls for as long as one minute.

Male Village Indigobirds in a local neighbourhood within a few kilometres of each other share the details and sequence of the same 24 song themes. These songs are delivered together as a set and form a local song dialect. Males a few kilometres away have a different set of song themes, which they share in another song dialect.

Other indigobird species similarly mimic the songs and calls of their own host species. They also sing non-mimetic songs, which they share with other males within the local population, or “song neighbourhood”. All adult males give the begging call of a young indigobird, which is the same as the begging call of the young of certain firefinches, specifically the African Firefinch and Jameson’s Firefinch, and which differs from the begging calls of other host species.

Among the whydahs, male paradise-whydahs mimic songs of a pytilia (Pytilia) species, the Shaft-tailed Whydah imitates its host the Violet-eared Waxbill, and the Straw-tailed Whydah mimics its host the Purple Grenadier (Granatina ianthinogaster). Mimicry of the calls or songs of the host species by Pin-tailed Whydahs has not been recorded, or, at least, it has not been recognized. The Steel-blue Whydah usually parasitizes nests of Red-rumped (Estrilda charmosyna) and Black-faced Waxbills (Estrilda erythronotos), but the songs of this whydah so far recorded seem not to mimic the songs and calls of these waxbills. Even so, male Steel-blue Whydahs north of Kavirondo Gulf, in Kenya, do mimic the songs, contact calls, alarm calls and begging calls of the Red-cheeked Cordon-bleu (Uraeginthus bengalus), which may be a local host species.

The Cuckoo Finch does not mimic the songs of its host species, the prinias (Prinia) and cisticolas (Cisticola) in the family Cisticolidae. Its song bears similarities to those of certain ploceids and estrildids, respectively the Village Weaver (Ploceus cucullatus) and Dybowski’s Twinspot, and to the non-mimetic songs of the indigobirds and the Straw-tailed and Shaft-tailed Whydahs.

Indigobirds learn the songs of their foster species and the songs of older adult indigobirds. A male Village Indigobird reared by a pair of Red-billed Firefinches gives the song of a firefinch, but not necessarily the same song as that of his individual foster parent. A male has three mimicry themes in his song repertoire, rather than just one; the latter would be expected if he learned his mimetic song only from his own foster father, as a male firefinch has only one song theme. Indigobirds appear to copy each other’s mimicry, and all males in a local population have the same set of local firefinch songs.

In the field, juvenile indigobirds associate with others of their species shortly after the end of the period of parental care. They are attracted to the call-sites of singing conspecific males, and they join the conspecifics that feed nearby; this may be the time when the young learn additional songs of their own species. In Zambia, a few indigobirds in juvenile plumage in July utter subsong, with recognizable song mimicry, and court females with a hover display, in a “school for song-learning” group near the call-site.

Adult male indigobirds modify their songs from year to year. They alter the details of each song theme to match the current song themes of another male in their song neighbourhood, as a result of which the same song changes occur both within and among individuals. All 24 song themes in a male’s repertoire, including the mimetic songs, change slightly within a season and from one breeding season to another, and these changes accumulate over the years. The change is related to the mating success of the singing males. When a male’s song changes within a season, his neighbours copy the changes only when the innovation originates in the male with the highest rate of female visits and matings. When a male moves from one song neighbourhood to another, he often takes on the songs of the new neighbourhood and no longer sings the songs of his old song dialect. Adult song-learning does, however, have its limits in so far as the male continues to imitate songs and calls of the same host species throughout his lifetime. These year-to-year changes in the continual cultural evolution of songs have been recorded in the field in Zambia for colour-ringed Village Indigobirds and Purple Indigobirds.

In experimental studies of song-learning, one male indigobird copies the mimetic songs of another male indigobird, and this is repeated across three or more generations of song transmission. A male also learns the non-mimetic songs of other males that mimic his own foster species. Further, when a male is reared by another species of foster parent, he learns and sings the song of the latter, and not the song of his normal host species, even if he lives in circumstances where his normal host sings in the same aviary.

Female indigobirds are attracted to a male which gives mimetic songs like those of her foster parents. In cross-fostering experiments, when females are reared by a new species, the adult female is attracted to indigobird song that mimics her foster species, rather than to mimicked song of her species’ normal host. In addition, breeding females reared by their normal host species seek out nests of that host, and females reared by the new host species seek out the nests of the new host and lay in those nests. Both the songs and the host association are behaviourally imprinted upon the female during her period of foster care.

The function of song mimicry is known from the social context of song in the field and from experiments with birds in captivity. Female Village Indigobirds are attracted to songs of their host species, and to male indigobirds that mimic these songs. They develop large ovaries when they hear these songs. A male’s song mimicry is not directed at a nesting host but, rather, it is directed at a conspecific female. A male’s mimicked songs signal his early experience in being reared by a foster species. It is to a male’s advantage to attract a female reared by the same foster species as he himself was, and it is to a female’s advantage to mate with a male reared by the same species as her own foster parents. In this way, male and female have offspring that are likely to be reared by this host species, in as much as their chicks match the mouth pattern of the host and can gain the advantage of nestling-mouth mimicry in a mixed brood.

Although the female indigobird learns the songs of her foster species as a young bird, and when adult is attracted to these songs, she does not exhibit any courtship behaviour towards the foster species. She is attracted to a male indigobird that mimics her own foster species, and she is attracted to the singing foster species when the time comes for her to parasitize a nest. Her mate choice involves both the song, which she learns from her foster parents, and an innate recognition of a suitable mate. In a cross-fostering experiment, Village Indigobirds were reared by a novel foster species, the White-rumped Munia (Lonchura striata). All of these indigobirds were taken as eggs where they had been laid in a host nest in an aviary. The eggs were placed under the foster finch in a birdroom where there were no indigobirds, the only birds in social and auditory contact with the young indigobirds being their foster species. These young indigobirds were moved in the following year to an outdoor mixed-species aviary. The female indigobirds with no previous experience of other indigobirds were attracted to and