Waxbills and Grassfinches (Estrildidae)

(Estrildidae)

Class: Aves

Order: Passeriformes

Suborder: Passeri (Oscines)

Family: Estrildidae

Thumbnail description
Small, often brightly colored, highly social birds with large, conical bills

Size
3.5–6.7 in (9–17 cm)

Number of genera, species
29 genera, 129 species

Habitat
Savanna, forest, and semi-desert

Conservation status
Endangered: 2 species; Vulnerable: 8 species; Near Threatened: 6 species

Distribution
Sub-Saharan Africa, southeastern Asia, Australia, and South Pacific islands. Small populations have been introduced throughout other parts of the world

Evolution and systematics

Weaverfinches, or estrildids, are related to the weavers with which they were formerly placed in the family Ploceidae. They do, however, differ clearly from weavers not only in external appearance, but also in behavior and in a number of digestive tract characteristics. For these reasons, they are now generally considered a distinct family that has diverged far from the common ancestral stock shared with the weavers. Sibley and Monroe, on the basis of genetic studies on DNADNA hybridization, have grouped several of the existing families, including Estrildidae and Ploceidae, into the Passeridae family. Although there is presently no consensus among ornithologists about their work, it will certainly play an important role in avian taxonomy in the future.

Physical characteristics

Weaverfinches are relatively quite small in size ranging from the 3.5 in (9 cm) quailfinches (Ortygospiza spp.) to the 6.7 in (17 cm) Java sparrow (Padda oryzivora). There are about 29 genera with about 129 species. Particularly characteristic of the weaverfinches are the projections or swellings of thickened connective tissue known as tubercles or papillae shown by the young at the edges of the bill and at the gape. These are a striking white, blue, or yellow color, often emphasized by black surroundings. In the Gouldian finch (Chloebia gouldiae) and the parrotfinches (Erythrura spp.) the tubercles have developed into organs which seem to reflect light and thus show up in the semi-darkness of the nest. A characteristic of the weaverfinches that varies according to the genus and species is the gape pattern of the nestlings. These patterns consist of dark spots or lines on the palate, the tongue, and the floor of the mouth. In contrast to the colored bulges at the angles of the gape, the patterns in the interior of the mouth are, in many cases, retained for life.

The plumage is sometimes inconspicuous, but often very attractively colored. It is never, as in many weavers, striped in a sparrow or bunting-like fashion. Adult plumage is attained over a period of six to eight weeks without a distinguishable intermediate phase as in the fringillid finches. As in the whydahs, the outermost primary is generally very much shortened. Using the physical characteristics of an individual's plumage, one can usually place it in one of the many Estrildidae groups. For example, the parrotfinches usually display combinations of vibrant greens, blues, and reds in contrast to the munias and mannikins (Lonchura spp.), which are usually characterized by various shades of browns and tans. For some of the groups, the name is descriptive and indicates that group's distinguishing feature, such as in the olive-backs (Nesocharis spp.), the crimson-wings (Cryptospiza spp.), and the bluebills (Spermophaga spp.). Sometimes, however, a group's name can be misleading, such as with the firefinches (Lagonosticta spp.) whose plumage usually contains colors ranging from pink to crimson red, but never what most would consider a "fiery" red. The patterning of the plumage can also help place estrildids into groups. The twinspots have white spots on their underparts and sides with each feather containing two spots, the characteristic for which they are named. The pytilias (Pytilia spp.), on the other hand, have barring in these areas in addition to a bright red face in the males. The firetails (Emblema spp.) can have either barring or spots on their sides and underparts, but their distinguishing characteristic is their bright red rump and tail.

The bill of the almost exclusively insectivorous species, such as the negro-finches (Nigrita spp.) and the flowerpecker weaver-finches (Parmoptila spp.), is as slim as that of warblers. In species that eat large seeds, like the bluebills and the seed-crackers (Pyrenestes spp.), it is almost as thick and strong as that of hawfinches. The waxbills (Estrilda spp.) fall somewhere in the middle of this size range with their often bright red "waxy" bills. Tail size is also quite variable, ranging from the long central tail feathers of the grassfinches (Poephila spp.) to the unusually short tail of the quailfinches.

Distribution

The family Estrildidae is an Old World family with a natural distribution around and south of the equator in the Ethiopian, Oriental, and Australasian biogeographic regions. Most species within this family can be found in Africa. The negro-finches and flowerpecker weaver-finches can be found in equatorial east central Africa. The olive-backs have very small, often patchily distributed ranges within central Africa. The other Africa-endemic groups have more diversified ranges. These include the pytilias, the multiple genera of twinspots, the crimson-wings, the seedcrackers, the bluebills, the firefinches, the waxbills, the quailfinches, the cordon-bleus (Uraeginthus spp.), and the two species in the genus Amadina. The munias and mannikins have radiated throughout Africa, including Madagascar, across southern Asia, and into Malaysia, Indonesia, Australia, and surrounding islands. The parrotfinches are concentrated in Southeast Asia throughout its many islands as well as the mainland. Some species have a very limited range sometimes consisting of only a single island, a major disadvantage to the conservation of a species when a threat to its population arises. Australia, like Africa, has its own set of endemic estrildid groups. These include the grassfinches, the firetails, the two species within Neochmia, as well as the monotypic genera Chloebia and Aidemosyne. Introduced populations of several estrildid species have been established throughout the world from either intentional releases or from escaped captive birds.

Habitat

Most weaverfinches live in grass or bush steppes, savannas, and open dry area forests. A few have penetrated deserts and semi-deserts, particularly in South Africa and central Australia. Others resumed their family's apparent earlier position as true forest dwellers, particularly in western and central Africa, southeastern Asia, and the Indo-Australian insular area. Recently, several species have become closely linked with man and have moved into fields and gardens, some even into city parks. The red-billed firefinch (Lagonosticta senegala) comes into native huts in its search for food. Zebra finches (Taeniopygia guttata) and crimson finches (Neochmia phaeton) breed on and in buildings.

Behavior

In recent years the display behavior of weaverfinches has been studied with particular intensity. The bond between members of a pair, and sometimes among members of a small flock, is usually strong. Unlike in many groups of birds, male weaverfinches do not feed the female as part of a courtship ritual. In most species the male has a "display dance" in which it sings and either hops towards the female or performs characteristic bows or stretching movements while hopping about in front of the female. Many avadavats (Amandava spp.) and some Australian grassfinches hold a feather or a grass stalk in the bill during this display, apparently as a nest symbol. The female weaverfinch's way of indicating readiness for mating is unique among songbirds. She cowers on a branch and trembles her tail, which is held vertically while the wings are kept still. In contrast, other songbird females tremble their wings and keep the tail quite still.

The song of weaverfinches is often soft and sometimes inaudible to human ears. This may, in part, be due to the fact that weaverfinches do not use songs to indicate aggression or territoriality, and therefore do not need their song to be heard by neighbors. An often unmusical and short song is uttered just loud enough for a nearby female to hear as part of the male's courtship. Unlike other vocalizations, the song is not instinctual. Instead, it is learned during a very narrow window during development of the fledgling (25 to 35 days of age for the zebra finch). Captive birds raised by a different species often learn the song of the male foster parent, but not the other calls. However, they can learn the meaning of the foster parents' calls and will often respond with the corresponding call from their own repertoire.

Feeding ecology and diet

The predominant food of weaverfinches is half-ripe and ripe grass seeds. Particularly in the breeding season many also take arthropods. They are attracted by nuptial swarms of ants and termites at the beginning of the rainy season and they pick the insects up from the ground or sally after them like flycatchers in a short fluttering flight. Some Australian weaverfinches have developed a manner of drinking which is evidently unique among passerine birds and occurs outside this order in only a few groups of birds. They suck in the water like pigeons, immersing the bill almost up to its base. This behavior has evolved independently several times in birds of arid areas probably because the birds are exposed to danger at the water holes. By sucking up the water they can reduce the time required to stock up with fluid.

Reproductive biology

Estrildid nests are always roofed over and are, as a rule, almost spherical with a diameter of about 4–8 in (10–20 cm). Many species attach a long entry tube to the nest, but this, in contrast to many weaver nests, never hangs down vertically. Usually both partners participate in nest building. Males mainly gather the nesting material and the females build with it. Most species use fresh or dry grass stalks and many line the nest cup with feathers or other soft materials. In many cases nests are built outside the breeding season as well and these are used for roosting. In many species a whole group of birds use such sleeping nests together. Nests are usually placed in bushes or low trees. Some species nest on the ground, while others suspend their nests between grass stalks or reeds or nest in tree holes.

The clutch usually consists of four to six eggs, with rare cases of up to nine. Both sexes incubate eggs and brood young. In the daytime they relieve one another at approximately equal intervals of about one and a half hours, while at night both sexes in many species sit together in the nest. The male, when appearing for relief at the nest, often brings as a "present" a bit of grass or feather. The incubation period is 12–16 days. Young receive mainly half-ripe seeds. Parents regurgitate these in small portions from the crop and push the food into the young bird's gape. The nestling with wide open bill grabs the adult's bill about the angles. The begging posture of the young is also unique among passerines. They do not stretch the head and neck towards the parents, but lay the neck flat on the nest floor, turning only the gape upwards. The chick's bill is wide open, displaying the characteristic pattern inside the mouth and the head is moved from side to side and turned in a lively manner. There are no trembling wing movements so characteristic in other food-begging young birds. This begging posture is retained after leaving the nest. The nestling period lasts about three weeks, which is surprisingly long for such small birds. Even after fledging, the young have not definitely left the nest, for the parents guide them back to it for sleeping and, at first, even for feeding. Young remain dependent on the parents for food for one or two weeks after fledging.

Some species of weaverfinches serve as brood hosts for the whydahs and indigobirds (Vidua spp.). Each parasitic species has a corresponding estrildid host species with which it shares many similarities including juvenal plumage as well as the characteristic species-specific mouth markings. This result of convergent evolution is used to fool the host species into accepting their "adopted" charges. The similarities between the groups have even fooled ornithologists in the past to place them within the same family. The whydahs and indigobirds are now rightly placed in family Ploceidae with the weavers, their true relatives.

Conservation status

According to the IUCN, the family Estrildidae contains six species which are considered Near Threatened, eight which are Vulnerable, and two that have reached the status of Endangered. The reason for the decline in most of these species' numbers is multifactorial. Several species, including the green avadavat (Amandava formosa), the green-faced parrotfinch (Erythrura viridifacies), and the Timor sparrow (Padda fuscata), which are all listed as Vulnerable, have suffered from habitat loss and modification in addition to trapping for the pet trade. Early and strict laws governing the exportation of Australian fauna have nearly eliminated the threat of trapping for the pet trade on that continent. However, habitat modifications in the form of fragmentation, overgrazing by cattle, and widespread burning have affected the populations of the star finch (Neochmia ruficauda), the diamond firetail (Stagonopleura guttata), and the Endangered gouldian finch in Australia. Having a range that is limited only to a small island or two means that a threat to an already decreased population can have major consequences. This has been the case for several parrotfinches including the royal parrotfinch (Erythrura regia), considered by some ornithologists to be a subspecies of the red-headed parrotfinch (Erythrura cyaneovirens). This species has felt the impact of logging and cattle grazing in its native range of Vanuatu and Banks islands. However, the Java sparrow, another island denizen with a small population, is gradually succumbing to the combined effects of trapping for the pet trade, killing, and egg-robbing because of their effects on rice crops, and hunting for food. Population numbers are not the only factors considered when classifying the conservation status of a species, however. Population trends play a major role as well. This is well illustrated by comparing the Anambra waxbill (Estrilda poliopareia) and the pink-billed parrotfinch (Erythrura kleinschmidti), both of which have populations fewer than 1,000 individuals. The former's population is stable and it is therefore classified as Vulnerable whereas the latter's population is declining, earning it an Endangered status.

Significance to humans

Weaverfinches, in contrast to many other songbirds, have neither long nor very attractive songs, and only on a few rare circumstances when they are handfed do they become tame. Nevertheless, they have, throughout the history of aviculture, been among the most popular and frequent pet and aviary birds. Several species such as the Java sparrow, the zebra finch, and the gouldian finch have reached the status of domesticated species, a rare title among birds kept as pets. The Bengalese or society finch has never occurred in the wild. Instead, it is a form of the white-backed munia (Lonchura striata) that was domesticated in the Far East during the early 1700s or even earlier. The deficiencies of weaverfinches are balanced in most species by attractive colors and patterns. They are lively, sociable, in most cases peaceable, and not demanding in their maintenance. They are particularly suitable for large aviaries where a mixed group of different species and colors can often be kept harmoniously. If planting within the aviary and feeding are suitable, breeding can usually be expected once the pair becomes established.

In contrast to their pet quality, some estrildids, namely the munias and mannikins, can have a devastating impact on agricultural crops such as rice. This often leads to their widespread persecution. Hunting of the pests becomes a sport and children are sometimes hired to collect eggs from nests. Some species, such as the Java sparrow, are also hunted for food, while others, like the spotted munia (Lonchura punctulata), are collected for religious purposes.

Species accounts

Resources

Clement, P., A. Harris, and J. Davis. Finches and Sparrows. Princeton: Princeton University Press, 1993.

Goodwin, D. Estrildid Finches of the World. Ithaca, New York: Cornell University Press, 1982.

Pizzey, G. A Field Guide to the Birds of Australia. Princeton: Princeton University Press, 1980.

Restall, R. Munias and Mannikins. New Haven: Yale University Press, 1997.

Simpson, K. and N. Day. The Princeton Field Guide to the Birds of Australia. Princeton: Princeton University Press, 1996.

Zann, R. The Zebra Finch. New York: Oxford University Press, 1996.

Zimmerman, D., D. Turner, and D. Pearson. Birds of Kenya and Northern Tanzania. Princeton: Princeton University Press, 1996.

Stripling, R., A. Kruse, and D. Clayton. "Development of Song Responses in the Zebra Finch Caudomedial Neostriatum: Role of Genomic and Electrophysiological Activities." Journal of Neurobiology 48 (2001): 163-180.

Birds Australia Nest. Birds Australia. 14 November 2001.

2000 IUCN Red List of Threatened Species. International Union for Conservation of Nature and Natural Resources. 14 November 2001. .

UNEP-WCMC Database. United Nations Environment Programme World Conservation Monitoring Centre. 20 November 2001. .

[Article by: Joseph Allen Smith]