HBW15 - Family Text: Viduidae (Whydahs and Indigobirds)
Family VIDUIDAE (WHYDAHS AND INDIGOBIRDS)
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).
Open country, from grassland to open woodland.
2 genera, 20 species, 28 taxa.
No species threatened; none extinct since 1600.
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 (). 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 . 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 () and other males mimic the Black-bellied Firefinch (), and in south-east Nigeria some males mimic the . 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.
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.
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.
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.
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 mated with male indigobirds that had been fostered by White-rumped Munias and mimicked the songs of this foster species. The female indigobirds showed no sexual behaviour towards the nesting munias in these aviaries, and they visited the munias' nests to lay their eggs. The female indigobirds appear to have innately recognized the male indigobirds as mates by their appearance and courtship behaviour, as these females responded appropriately when courted, even though they had never experienced a male indigobird in their early life. The females are attracted to the songs that sound like those of their own foster parents, and the next step in breeding is to respond to the behaviour of the male indigobirds and to copulate, and then to lay their eggs in the nest of the foster species.
Some information is available on some other Vidua species. For example, in a mixed-song population of Cameroon Indigobirds in which some males mimicked songs of the African Firefinch and others copied songs of the , genetic markers indicated that father and son nearly always mimicked the same host species. Nevetheless, one father had a son that gave songs of the African Firefinch and another son that sang Black-bellied Firefinch songs. The genetic markers generally indicate a rather low degree of interbreeding between the two song populations.
Young males of the Straw-tailed Whydah learn the songs of their foster parent, normally the Purple Grenadier. When reared by another foster species, the males learn the vocalizations of that other fosterer. Each male has three or four loud mimicry song themes. Songs of males are nearly identical to those of other males nearby, populations 2-4 km apart have different songs, and the songs differ regionally. Chatters first develop at 32-35 days of age, and songs are given within the first year; the chatter is innate, whereas songs are copied from other whydahs. Begging calls incorporated in the songs of Straw-tailed Whydahs are unlike the begging calls of young Purple Grenadiers; the adult male whydah mimics the adult calls and songs of the host grenadiers. More field studies are needed in order to record the begging calls of whydahs and their host species.
Captive female Broad-tailed Paradise-whydahs lay in nests in aviaries when they hear songs of their host species, the Orange-winged Pytilia (Pytilia afra). Female Long-tailed Paradise-whydahs are attracted to songs of their host, the Melba Finch, and not to Orange-winged Pytilia songs; in aviaries, they sometimes lay when they hear songs of the Melba Finch. Males of this paradise-whydah mimic songs of the Melba Finch, and in natural conditions the females are attracted to male whydahs giving these songs.
Behavioural imprinting and song mimicry by Vidua species bring together in mate choice the males and females that were reared by the same host species. This behavioural adaptation leads to the production of chicks with mimetic mouth colours that fit well into the parasitized broods of this host species.
Food and Feeding
Members of this family are almost entirely granivorous. They consume mainly the small seeds of annual grasses, taking these on the ground after the seeds have ripened and fallen from the stems. Indigobirds and whydahs take the same kinds of grass seed as do their estrildid host species. A few species are known to feed very occasionally on insects, too. The Pin-tailed Whydah sometimes feeds on flying termites (Isoptera), and the Village Indigobird similarly exploits small termites when they emerge during the rains. Straw-tailed Whydahs supplement their diet of small grass seeds with both larval and adult insects, which they catch on the ground. The Cuckoo Finch has been seen on rare occasions to take insects, sometimes hawking these at dusk. It feeds its young with insects, including caterpillars and wasps (Hymenoptera). Wilsonçs Indigobird (Vidua wilsoni) will associate with domestic fowl on chicken farms, exploiting the feed put out for the chickens. Laying females of the Cuckoo Finch and many of the Vidua species eat the eggs of their estrildid host.
When foraging, viduids utilize a technique known as the "double-scratch". Using both feet nearly simultaneously, they scratch the ground in order to uncover seeds in the dust; they then hop backwards and pick up the seeds. The bird dehusks grass seeds in the bill, using the tongue to roll them, one seed at a time, forwards and back against the ridge of the palate. In a feeding bout, an individual gathers and holds in the crop as many as several hundred small seeds. The act of feeding while perched on grass stems and when the seeds are still on the stems is uncommon. Indeed, it has been noted only for the Pin-tailed Whydah. In a fledged family group consisting of the host species and Vidua young, the latter feed together with their foster parents and foster siblings.
Cuckoo Finches forage on the ground and on erect stems of fruiting heads. They use the bill to crush large seeds, such as sunflower (Helianthus) shells. They have not been observed to double-scratch in the field, nor have captives in an aviary been seen to utilize this method with small grass seeds scattered on sand. The Cuckoo Finch takes grit and sand, which serve to pulverize hard seeds in the crop; Vidua species apparently do not do so.
Drinking is performed in much the same manner as it is by most other passerines. The viduid finches tip forwards and sip water, before lifting the head higher than the body in order to take in the liquid.
The Cuckoo Finch, the whydahs and the indigobirds are brood parasites, laying their eggs in the nests of other kinds of songird. The nesting birds, the hosts, rear the young brood parasites along with their own brood.
Observations made in the field, in museum collections and in breeding aviaries all led to the discovery of brood parasitism. The phenomenon was first detected for the Pin-tailed Whydah. The earliest observation, in 1895, was made in Uganda by F. J. Jackson's collector, Baraka. Jackson encouraged him by promising a reward for finding the whydahçs nest. Baraka found that the whydah did not build its own nest but that, rather, it laid an egg in the clutch of a Common Waxbill (Estrilda astrild). Baraka and Jackson then found other nests parasitized by the whydah. In 1938, Jackson wrote that "Baraka... is due the credit of solving the mystery". In South Africa, A. Roberts independently discovered that the whydah parasitized the waxbill. He noted a Zulu report that "King-red-beak", a colloquial name for the Pin-tailed Whydah, "is reared out of every ‘Rooibekje's' (Estrilda astrild) nest". Roberts followed up this report and found waxbill nests with both small and large eggs, nests with two kinds of young, and a nest from which a female whydah flew, perched and wiped her bill; the nest had a half-eaten egg of a waxbill and a large egg of the whydah. In 1925, F. E. O. Mörs reported that he had found waxbill nests with young whydahs in the brood; he distinguished their eggs and their young, and over 30 years he found no whydahs building their own nests.
The Cuckoo Finch was discovered to be a brood parasite after V. G. L. van Someren, in 1912, photographed and collected a young bird in the nest of a Rattling Cisticola (Cisticola chiniana), at the time identified as a nest of a Cardinal Quelea (Quelea cardinalis). He identified the young as that of a Cuckoo Finch only after Roberts had photographed young Cuckoo Finches in nests of prinias and cisticolas. Chicks thought to have been of "V. macroura" found in cisticola nests in Ethiopia were saved as specimens in the British Museum (Natural History); examination of these reveals that they are, in fact, young Cuckoo Finches.
In South Africa, Mörs reported Shaft-tailed Whydahs to be brood parasites of Violet-eared Waxbills, the nestlings of the two species growing up together in waxbill nests. Roberts found young Long-tailed Paradise-whydahs in a party of Melba Finches, and a large egg appeared in a Melba Finch nest when a female whydah was there. Other cases of brood parasitism were discovered in museum material in cases when two kinds of juvenile had been collected together. First, C. F. von Erlanger's Ethiopian collection of Purple Grenadiers in the Berlin and Frankfurt museums, in Germany, in fact had more than one species: the long-winged, short-tailed birds were darker and had no blue on the rump. When comparing museum specimens, R. Neunzig recognized the long-winged individuals as Straw-tailed Whydahs. Secondly, Neunzig, noting the similar distributional ranges of the Steel-blue Whydah and the Red-rumped Waxbill in East Africa, reconsidered van Someren's identification of a whydah egg in this waxbill's nest; he described the similar juvenile plumages of the two species, and he reasoned that they formed a species pair consisting of a brood parasite and its host.
Neunzig was aware of the existence of brood parasitism among the finches, he knew of large and small eggs in the nests of certain estrildid finches, he knew of the similar juvenile plumages of Vidua and certain estrildids, and he recognized the matching geographical distributions of these Vidua species and the corresponding estrildid species. From these observations combined with examination of museum material, he concluded that the Vidua were species-specific brood parasites, and both the plumage and the mouth patterns and colour of the young mimicked those of the young of their host species. Later field observations have supported Neunzig's conclusions.
Species-specific brood parasitism by the indigobirds was first discovered among Village Indigobirds. In the second half of the nineteenth century, in Sudan and Ethiopia, T. von Heuglin reported the indigobird and the Red-billed Firefinch as building nests of grass and feathers in the roofs of houses, in holes in walls, and in trees, and even as living in mixed families when the young were out of the nests. Elsewhere, field observers commented on seeing these birds together. In Kenya, van Someren reported an indigobird nest with three eggs; a male sang nearby, but indigobirds were not seen to visit the nest or to rear the young, and the nest was probably that of a firefinch. In Gambia, G. Hopkinson, in a 1921 letter to D. A. Bannerman, stated that he found indigobirds to be common around villages with firefinches. He suspected that the indigobird was a species-specific brood parasite of the firefinch. At one nest that he found, the young occupants, two young firefinches and an indigobird, were in the act of leaving the nest; when he captured the young indigobird, the adult firefinches fed it while an adult indigobird nearby showed no interest in the young. In the 1930s, in Mali, G. L. Bates saw indigobirds and firefinches as they entered the same nest-holes, and he commented that the two species might always breed together unless the indigobird were, in fact, parasitic on the firefinch. To the east, in Nigeria, F. C. R. Jourdain and R. Shuel found a female indigobird with a shelled egg in her body, dead in a nest; apparently she had entered a firefinch nest, caught her foot and died.
Neunzig remarked on the close similarity in plumage and mouth markings of young Village Indigobirds and Red-billed Firefinches and, on the basis of mouth markings and Heuglin's field observations, he concluded that the indigobird was a species-specific brood parasite of the firefinch. Nevertheless, as late as 1938, Jackson suggested that the indigobirds sometimes nested or took over the nest of another bird and reared their own young, and sometimes were brood parasites. The first detailed field study, in the 1950s, was by G. J. Morel and M. Y. Morel in Senegal, where Village Indigobirds were species-specific brood parasites of the Red-billed Firefinch. Subsequently, the work of J. Nicolai revealed that many Vidua species, including this indigobird, mimicked the songs of their host species. Fieldwork has confirmed Nicolai's ideas of the host specificity of song mimicry and brood parasitism in most members of the genus Vidua.
Although some aviculturists wrote that indigobirds and whydahs nested and reared their own young, others reported that the young were reared by estrildid finches. Indeed, some aviculturists reported both nesting and brood parasitism for some Vidua species. Aviculture, however, was not at the time held in high regard by field ornithologists or systematists. In addition, sceptics suspected that birds might behave differently in aviaries from the way in which they do in the field, and aviary observations were discounted when they did not concur with field reports. Reports of the viduid finches building a nest and rearing their own young are in error.
Members of the Viduidae time their breeding to coincide with the breeding season of their hosts. Males develop enlarged gonads and breeding plumage in the weeks before the host species builds its nest. In females, the final stages of egg development take place when they see or hear the nesting host species. In captivity, female Village Indigobirds and Long-tailed Paradise-whydahs have laid eggs when they heard the songs of their host species, even when they had no contact with conspecific males or the host. The laying histories of female finches have been determined by examination of the ovary, including post-ovulatory follicles and growing follicles, and of the oviduct. In the parasitic finches, the Viduidae, the clutch size is variable, usually three or four eggs; in this case, clutch size is calculated as the number of eggs that develop in a set and are laid on successive days, and corresponds to a clutch in the nest of a host finch. A total of three eggs is laid, more than one nest being exploited, or two or three eggs are laid in a single nest; both strategies have been observed for female indigobirds in breeding aviaries. The incubation period is about two days shorter than that of the host species.
The female viduid searches and finds a host's nest on her own. Village Indigobird females perch and look on as firefinches gather nest material, especially a feather. They then follow the hosts to the site, where the male firefinch displays the feather in his bill as he courts his female. Females also search through thatch-roofed houses and chicken and pig barns, the habitat where the firefinches have their nests. In the case of the Village Indigobird and the Shaft-tailed Whydah, the female sometimes enters the host's nest and lays her egg even when an adult host is present in the nest. Eggs of Vidua are white and unmarked, as are those of their estrildid hosts. They tend to be larger and more rounded in shape than are their hosts' eggs, yet not all eggs are identifiable by size and shape. They can be distinguished with certainty only if they hatch and the young are reared and identified, or if the eggs or chicks are identified by molecular-genetic methods. The most reliable means of determining the identity of suspected brood parasites are the distinctive mouth markings or feathered plumage of the nestlings, and the use of genetic techniques to identify eggs and young. For some Vidua species, formed eggs have been found in the oviduct of breeding females, thus providing additional information on their appearance. After they leave the nest, young Vidua are distinctive in plumage, and they lack the red or blue rump of the young of the host species. Fledglings and young juveniles forage together with family groups of the host, the young being less active in their movement. A week or two after they fledge, the juveniles join flocks of adult Vidua.
As mentioned in the above paragraphs, Cuckoo Finches lay in the nests of prinias and cisticolas in grassland and marshes and in savanna and open woodland. These hosts rear the young Cuckoo Finch, usually the only chick in the brood that fledges. This is because the Cuckoo Finch, when she lays her egg, removes the host's eggs, thereby leaving her own young brood parasite as the only chick in the nest. Occasionally, a host lays after the Cuckoo Finch has done so, and it may then rear its own young along with the parasitic nestling. Sometimes, more than one Cuckoo Finch egg is deposited in the nest and two chicks survive and fledge. The survival of more than one chick, including either a host chick or another brood-parasitic one, indicates that the young Cuckoo Finch does not evict its nestmates.
Nestling and fledgling whydahs and indigobirds are fed by their foster parents. They crouch, twist the head and neck, wave the head from side to side, and beg with the head turned to one side or even upside-down, in the manner of the young of their estrildid hosts. The nestlings and fledglings are fed with seeds regurgitated by their foster parents. In contrast to the whydahs and indigobirds, the young Cuckoo Finch begs in an upright posture, without waving the head, and it feeds directly, taking insects held in the fosterer's bill.
Indigobirds and whydahs lack a strong pair-bond. They are, in fact, socially promiscuous. A female visits several males and will sometimes mates with more than one of them, and a male courts several females. Their mating system is explained as being due to the absence of parental care. The male indigobird sings throughout the day, centring his behaviour on one bush or tree, referred to as the "call-site". He defends this territory, sings, and chases other males, keeping them from the site. When chasing off intruding males, the resident male stays lower than the intruder and closer to the site; the chase describes an ovoid ellipse, with a narrow focus at the branch from which the male sings. Singing males are often within hearing distance of one another, separated by no more than 100 m, but they can also be out of hearing range, as far apart as a kilometre or so.
A male Village Indigobird in the centre of his social neighbourhood remains on his call-site through most of the day. His neighbours and more peripheral males sing on their own sites and visit each other within this area, paying visits especially to the central male. Visiting males appear to listen to the singing male for about five to ten minutes, and then return to their own call-sites and sing. The central male remains on his site for more than 50 minutes in every hour, from a half-hour after sunrise until shortly before sunset. In contrast, peripheral males are away from their site for most of the day. A resident male generally uses the call-site year after year. When he disappears, another male often occupies the site, sometimes within an hour, and mates there on the next day. The central sites in a neighbourhood are traditional; when the older male disappears, presumably having perished, another male takes his place, and this process is repeated again for several years so long as the call-site tree remains intact. A call-site which few or no females visit remains unoccupied after the first male disappears.
When a female Village Indigobird visits his call-site, the male displays with aerial bobs and hovers, the plumage fluffed and the body bouncing. The two sometimes copulate on the perch. After display, the male flies to the ground near the tree, where the female usually joins him, and the two feed together, the male directing soft mimicry songs towards her. The female then visits several other singing males in succession, and is courted by each one; she returns to one of them, often the male in the centre of the local neighbourhood, and mates with him, although she sometimes mates with another male, as well. Males compete for sites and court the same females in a "dispersed lek". Females visiting the various sites may assess the males by the amount of time that they devote to singing, the successful central males being the most attentive to their call-sites. In a neighbourhood with about 20 Village Indigobird males singing within an area of a few square kilometres, the central male attracts more visiting females to its site than do peripheral males, and it gains nearly all of the matings.
Other species of indigobird exhibit breeding behaviour like that of the Village Indigobird. Neighbouring males visit each other at their call-sites, females visit the males and mate with one male on his call-site, and the male displays are the same bobs and hovers as those of the Village Indigobird.
The Straw-tailed Whydah and the Shaft-tailed Whydah chase and display in much the same way as do the indigobirds. The male sings from several trees within a few metres of each other; females visit more than one male and mate mainly with one of these males. Males of the Pin-tailed Whydah and Steel-blue Whydah sing on a call-site and sometimes display on the ground. Long-tailed Paradise-whydahs have a daily schedule of mid-morning and mid-afternoon behaviour, when they fly high in horizontal display over the grassy woodland, the tail trailing behind and the central pair of rectrices held above the other feathers at an angle of nearly 90 degrees. In display, they give chatters and non-mimetic songs; after a minute or so, they swoop into the top of a bush or tree, perch there, lift the head over the back, and deliver songs that mimic those of their host species, the Melba Finch. Female whydahs are attracted to mimicry songs; they fly to the males on their song perches and copulate with them.
Less is known about the breeding behaviour of the Cuckoo Finch. Adults and juveniles of this species form flocks both outside and within the breeding season. When not in a flock, a male sometimes sings at a single site for a few minutes, as has been recorded at Lochinvar National Park, in Zambia, and at Harare, in Zimbabwe. The male's courtship displays, with the wings raised, look more like the nest-displays of Ploceus weavers than like the displays of most male whydahs and indigobirds.
Viduid finches are resident. None of their populations is known to move long distances seasonally.
A few indigobirds ringed as adults have been recovered more than 20 km from their breeding site, but nothing is known about the juvenile dispersal of these birds. At the end of the breeding season, some whydahs form large flocks and move many kilometres, and a marked Shaft-tailed Whydah was recovered 150 km from its earlier site. In the dry non-breeding season, Cuckoo Finches appear in flocks far from their known breeding areas, and they may, in fact, be seasonal migrants.
Relationship with Man
In Europe, whydahs and indigobirds have been kept as cagebirds for centuries, being held in esteem for their song and colourful breeding plumage. Renaissance scholar Michel de Montaigne visited the Italian city of Florence in 1581 and saw them in the Medici aviaries. His description of a finch with la cue deus longues plumes commes celles dçun chapon, "a tail of two long plumes like those of a capon", would seem to refer to a paradise-whydah. Shortly thereafter, Aldrovandi, of the Universitá di Bologna, described and illustrated three Vidua in breeding plumage in the Medici aviaries: these appear to be the Village Indigobird, the Pin-tailed Whydah, and the Sahel Paradise-whydah. Aldrovandiçs encyclopaedic work was edited and published mainly after his death; his Ornithologiae was first published in 1599, with later editions published by the Studio Aldrovandi of Bologna in 1610, 1635, and 1645-1646. These finches had been painted in gouache on paper by Ligozzi, chief botanical painter of the Medici court, in his depiction of Ficus carica, the common fig, one of several illustrations commissioned for the visual catalogue of Aldrovandi and now housed in the Gabinetto Disegni e Stampe degli Uffizi in Florence. Aldrovandiçs illustration is a woodcut after this painting, identified by the postures of the paradise-whydah and indigobird and by the branches and leaves of the common fig.
Although not usually considered agricultural pests, the whydahs and indigobirds can sometimes be a nuisance locally. In the Fouta Djalon highlands of Guinea and Sierra Leone, they feed on the small seeds of cultivated fonio (Digitaria exilis), known also as "acha" or "hungry rice", before the harvest, while the seeds are still on the stem. This grain is the first food available to local human inhabitants after the season of rains, and people do their best to keep the birds from the crops until harvest time. Indigobirds also take drying manioc meal in Sierra Leone and feed on maize meal in South Africa and Malawi.
These birds are clearly well known to human inhabitants, as is evidenced by some local names for them. For example, the Arabic name for the breeding male Long-tailed Paradise-whydah, Abu Mus, meaning "father of the knife", describes the blade-like shape of this birdçs middle tail feathers.
It is of interest to mention the derivation of the generic names used for this family. The genus name Vidua and the English vernacular name of "whydah" refer to a widow, the Latin word for which is, indeed, vidua, or to a widowçs veil and train, the Portuguese word véu meaning "veil" and viúva meaning "widow". This is a reference to the male whydah's black upperparts and long tail. Another interpretation of the word "whydah" is that it is an imitation of "Ouidah", the name of a slave-trading port in Benin, in West Africa, from where the birds were exported along with human slaves.
Variations on the English name given to the Barka Indigobird (Vidua larvaticola) may give an insight into the way in which the family is sometimes perceived by humans. This species is frequently referred to as the "Bakra Indigobird" and the "Baka Indigobird". The name "Barka" refers to barkà , a Hausa greeting used in the region in north Nigeria where the birds were first observed; in some regions bakra is used. Both words are sometimes transliterated as baka, which also means "black", and bako, meaning "guest" or "stranger", either of which would be appropriate names for the brood parasite.
Status and Conservation
As a group, the Viduidae are common and not threatened or endangered in any way. Indeed, not one of the 20 species currently recognized is listed "officially" as globally threatened or placed in the conservation category of Near-threatened.
Species having a relatively small and localized distribution and a low population density may exist in low total numbers, but these appear not to be at any significant immediate risk. This applies particularly to the Togo Paradise-whydah and the Jos Plateau Indigobird (Vidua maryae), but also, to a lesser extent, to the Steel-blue Whydah. The last-mentioned, which is restricted to thorny scrub and thickets in the region from south Sudan, Ethiopia and north Somalia south to south-central Tanzania, is uncommon throughout its range; in some places in Kenya it has suffered from the effects of intensive grazing by cattle, and has become much scarcer than it was in the 1960s.
In West Africa, the Togo Paradise-whydah, found in open woodland and cultivation, is scarce throughout its fragmented range in Guinea, Sierra Leone, Ivory Coast, Ghana and Togo, perhaps with a small population also in north Liberia. This species' global population is not known with any degree of certainty, but it seems likely to be fairly small. The Jos Plateau Indigobird has the smallest geographical range of any member of the family. It is confined to a few rocky outcrops in semi-arid Guinean savanna on and near the Jos Plateau, in north Nigeria, where it extends into lightly farmed land and pasture, including grassland with scattered bushes. There are no available estimates of its global population, but this species is thought not to be at any immediate risk.
Indigobirds and whydahs, along with other finch-type species, are widely trapped for the cagebird trade. In Senegal, hundreds of thousands of birds are captured each year, under permit, for this purpose, yet this activity appears, perhaps somewhat surprisingly, to have no noticeable effect on population numbers. Viduids are trapped for the trade also in Guinea, Mali, Tanzania and Mozambique, and almost certainly elsewhere, too.
A few whydahs have become established as breeding birds in new regions where their host species also were introduced. In Puerto Rico, in the Caribbean, the Orange-cheeked Waxbill (Estrilda melpoda) was introduced more than 100 years ago and, again, around 1950. Pin-tailed Whydahs were introduced on this island through the bird trade and became established around 1960. They parasitize Orange-cheeked Waxbills and may parasitize other waxbills. In the 1970s, Pin-tailed Whydahs and waxbills were introduced also in Hawaii, and they bred there, but the whydahs are no longer present in these Pacific islands.
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