Weavers (Ploceidae)

(Ploceidae)

Class: Aves

Order: Passeriformes

Suborder: Passeri (Oscines)

Family: Ploceidae

Thumbnail description
Small to medium-sized passerine birds; bill conical or pointed; plumage plain yellow or black, or these colors in combination with red, brown, or orange, or else sparrowy brown; often there is a seasonal change in plumage, which may include development of greatly elongated tail-feathers; many species highly social, occurring in large flocks

Size
4.3–10 in, up to 28 in with elongated tail (11–25 up to 70 cm); 0.3–2.3 oz (9–65 g)

Number of genera, species
19 genera; 135 species

Habitat
Forest, woodland, swamps, savanna, semi-arid regions

Conservation status
Critically Endangered: 1 species; Endangered: 6 species; Vulnerable: 7 species; Near Threatened: 3 species; Data Deficient: 2 species

Distribution
Sub-Saharan Africa, Arabian Peninsula, South and Southeast Asia, Madagascar, Mauritius, Réunion, Comoros, Seychelles

Evolution and systematics

The fossil record of passerine birds is fragmentary and difficult to interpret. There are no conspicuous skeletal characters in ploceids that distinguish their bones from those of other passerine families, which makes it unlikely that fossils will provide clear evidence of their origins. However, both fossils and molecular data suggest that the passerine birds are an old group, and that many extant families could be as old as 40 million years. Thus the weaver group are likely to have evolved in Africa over a period during which there have been dramatic changes in climate, with the extent of forest cover fluctuating greatly. This would have promoted speciation in both forest and open-country habitats.

Earlier studies based on anatomy and other morphological characters linked the Ploceidae to the Estrildidae, another family of seed-eating birds which is primarily African. This was supported by the DNA-hybridization studies of Charles Sibley, but he placed both these groups as sub-families in a new family (Passeridae), along with the sparrows (Passerinae), wagtails and pipits (Motacillinae), and accentors (Prunellinae). This arrangement remains controversial, and we have followed a more traditional system. The four subfamilies of Ploceidae are most easily defined by their breeding habits: the buffalo weavers, Bubalornithinae (three species), build large nest structures of sticks and have a unique, rigid phalloid organ on the abdomen; the sparrow-weavers, Plocepasserinae (nine species), build nests of straight grass stalks which are not woven but stuck into the nest structure; the "true" weavers Ploceinae (103 species) weave a closed nest, with the entrance either at the side or below; the whydahs, indigobirds, and cuckoo finch Viduinae (20 species) are brood parasites, which lay their eggs in the nests of other birds. The position of the Viduinae is debatable. Behavioral studies by J. Nicolai suggested links to some Ploceinae such as the bishop-birds, whereas skeletal and molecular data imply that the waxbills (Estrildidae) are their closest relatives. The cuckoo finch (Anomalospiza imberbis) has usually been classified as a weaver, but both morphological and molecular data show that it belongs in the Viduinae.

The genus Ploceus (Ploceinae) is one of the largest bird genera at present with more than 60 species. An examination of skull characteristics suggests that there are several distinct groups within this genus, and new studies may lead to it being broken up into several distinct genera. The relationships between the African and Asian Ploceus weavers are not clear, and they have evidently been separated for a long time. The Foudia species on the Indian Ocean islands appear to be derived from the African genera Quelea or Euplectes, whereas the two Madagascar Ploceus species could be African or Asian in origin. These conclusions are based on plumage, nest structure, carotenoid pigments, and some skeletal characters; no molecular studies had been published by 2001.

Physical characteristics

The weavers have no defining physical characteristics which are shared by all or even most members of the family. The sexes may be virtually indistinguishable, even in the hand, or highly dimorphic. Tails can be short or extravagantly long. The bill is always straight, not curved, but varies from short and heavy to longer and quite slender. At the sub-family level, there is more consistency. Buffalo weavers are either mainly black or mainly white, with heavy seed-eater bills. Sparrow-weavers are all "sparrowy" brown in appearance, with some black or white plumage areas. There is no obvious seasonal plumage change in either of these groups, and little sexual dimorphism, although males are usually larger. Within the parasitic Viduinae, there is marked sexual dimorphism in plumage during the breeding season, after which males molt into a plumage which resembles that of the females. They can usually be disinguished from other small seed-eating birds by black stripes on the crown of the head. Male indigobirds are blackish, with pale or reddish bill and legs, in varying combinations. Male whydahs have mainly black or black-and-white breeding plumage with very long central tail feathers, which may be either narrow or broadened. The male cuckoo finch is canary-yellow in breeding plumage.

Among the Ploceinae, there are conspicuous differences between genera. Males are almost always larger than females, while sexual dimorphism in plumage is especially marked in polygynous species. However, even in dimorphic species, the males do not always have a seasonal plumage change. Eye color often changes with age from brown to red, yellowish, or creamy; in many cases only males have a distinctively colored eye. The bill color of male birds may change seasonally from brown to black, in response to increased levels of male sex hormones. The genus Malimbus is remarkably uniform. All species are predominantly black with some red, or in one case yellow, plumage; males and females differ in plumage, and juvenile birds have a distinctive plumage, different to both adults. There is no seasonal change in plumage. In contrast the open-country bishops and widows (Euplectes) all have sparrowy brown females, while males molt into a breeding plumage which is wholly or partly black, with either red or orange to yellow areas, and in some cases a long, black tail. Young birds resemble females, and males do not usually acquire breeding plumage until at least their second year. The large genus Ploceus includes species that are sexually dimorphic with or without a seasonal change in plumage, and species in which the sexes are identical. Black and/or yellow are the predominant plumage colors in males, with some green, brown, or orange, but never red, feathers.

Distribution

Weavers occur throughout sub-Saharan Africa, where all sub-families are represented. Only two genera of Ploceinae are found outside Africa; the fodies (Foudia) which are endemic to Madagascar and other Indian Ocean islands, and Ploceus with two species on Madagascar and five in Asia. One East African species, Rüppell's weaver (Ploceus galbula), also occurs on the Arabian peninsula. Several species are commonly exported as cage birds, and escapes or deliberate releases have led to their establishment, sometimes temporary, in other regions, including Australia, California, Portugal, Hawaii, St. Helena, and some islands in the West Indies. An Asian species, the streaked weaver (Ploceus manyar), is now established in the Nile delta in Egypt, and is believed to have escaped from Alexandria Zoo.

Habitat

Many weavers are associated with water, since they breed in wetlands, along rivers, dams, and lakes, nesting in reeds or other waterside vegetation. However, in these cases they often move to grassland or savanna during the non-breeding season. Several species may breed in wetlands, but also in trees far from open water, and have adapted well to man-modified habitats such as farmland. Only members of the sparrow-weavers and buffalo weavers are permanent residents of arid and semi-arid areas. Some species are exclusively forest birds, either in lowland or montane evergreen forest, and may spend much of their time in the canopy 100 ft (30 m) above the ground. All members of the genus Malimbus are strictly forest inhabitants.

Behavior

Although many species of weavers move about extensively during the dry season, these are local movements rather than predictable, long-distance migration. The red-billed quelea (Quelea quelea) does carry out predictable movements in many regions, and these seem to be correlated with rainfall patterns. This appears to be the only species that could qualify as a migrant throughout its range.

Although they may have a wide range of different calls, few weavers would be considered "songbirds" in the conventional sense. The songs that male weavers use to advertise their territories are often a harsh, repetitive chatter with no tuneful, musical notes. Some forest species do sing short phrases, sometimes as duets, which are more attractive to our ears. The parasitic indigobirds learn elements of the song of their host species while in the nest, and later incorporate these into the songs which they use in courtship.

Feeding ecology and diet

Categorizing weavers as insectivorous or granivorous is misleading. All species will take insects when they are available, and the young are often fed primarily insects, especially in the first days after hatching. There is frequently a seasonal change in diet, with seeds the main or even the only food source in the dry season, and insects more important in the rainy season. The heavy bill of the grosbeak weaver (Amblyospiza albifrons) enables the birds to open sunflower seeds, but they have also been seen to catch small frogs. Small lizards are on the menu of several other species in the wild. Fruit and berries are eaten readily, and nectar from plants such as Aloe and Erythrina. Here weavers are messy feeders, often eating the whole flower and stripping the plants, leaving with their faces caked with pollen. The Cape weaver (Ploceus capensis) is probably the main pollinating agent for the endemic South African crane flower Strelitzia regina.

Reproductive biology

Social organization in weavers shows clear correlations with habitat and feeding ecology, as J. H. Crook first demonstrated in his innovative comparative studies. Forest weavers are generally insectivorous and remain in pairs throughout the year, whereas seed-eating species of the open savanna associate in flocks, and form colonies for breeding. This, in turn, influences their breeding systems, with monogamy usual in the forest species, while many of the colonial weavers are polygynous, with one male mating in turn with a succession of different females.

Nests and nest construction have attracted most attention in this group of birds. The pioneering work of Nicholas and

Elsie Collias—who observed many species in the field, in captivity, and in museum collections—has provided an excellent framework for the evolution of nest-building in the family. In buffalo weavers and sparrow-weavers the technique is simple, with the nests formed as piles of interlocking material. These birds are associated with nests throughout the year, and thus maintain the structures with periodic building at all seasons; both sexes participate to some degree. In the true weavers (Ploceinae) nest-building is seasonal and these are short-lived structures, which mostly do not survive beyond one breeding season. The commonest pattern is for the male to produce a nest frame by weaving and knotting strips of material collected and prepared for this purpose. Once the female has mated and accepted a particular nest, she then adds the lining. However, the female's contribution varies greatly, depending on the mating system; in Jackson's widow (Euplectes jacksoni) the female is solely responsible for building and lining the nest, which is not on the male's territory.

Courtship in sparrow-weavers and buffalo weavers involves song and visual displays, generally near the nest structures. In the Ploceinae, among the monogamous forest species, courtship frequently takes place away from the nest, even before construction begins. By contrast the colonial species set up territories and build nests before intensive courtship starts, and the male often displays hanging at the nest entrance. Bursts of display activity may sweep through a colony as groups of females arrive, and the males all appear to be vying for their attention. In the polygynous species, each male will build a series of nests, and try to attract as many females as possible. Nest that are not accepted by females, or are no longer occupied, are often demolished. The male may then rebuild at the same site so that a single male masked weaver (Ploceus velatus) can build more than 20 nests over a three-month season. There is one exceptional species, Jackson's widow, in which males display at dancing grounds which constitute a lek: a male courtship arena which females visit to select a mate, after which they go off to nest and have no further contact with the male. In the parasitic Viduinae, males set up "song-posts" at which they display, and to which females are attracted. The breeding system is thus a form of lek, where the females visit males only to mate, although the males do not occupy a communal display ground.

Parental care is closely correlated with the mating system. In monogamous species, both incubation and feeding of the young may be shared equally between the partners, whereas in polygynous species the female normally does all the parental duties without assistance. In some cases, polygynous males may feed at the nest late in the season, or occasionally feed the young once they have fledged. Compared to some other African bird families such as the starlings, cooperative breeding in which several related or unrelated individuals help the parents to rear the young is rare in weavers. It occurs primarily in some of the sparrow-weavers in arid country, where a nesting tree forms a permanent base for the group, which roosts in the nests throughout the year. The situation in the parasitic Viduinae is especially interesting. Whydahs and indigobirds lay their eggs in the nests of waxbills; the eggs of both host and parasite are plain white, and similar in size. Waxbill young have highly distinctive mouth-markings, which are matched by the young parasites. The young are raised together, so although the waxbill parents have extra mouths to feed, they do not lose their whole brood as is often the case for cuckoo hosts. However, the cuckoo finch parasitizes small grassland warblers, and the host young seldom survive.

Conservation status

BirdLife International has produced a review of globally threatened birds, and an account of the Important Bird Areas of Africa. The major threat to weaver species is habitat loss, since some of them have very restricted ranges. Three island fodies are threatened both by habitat loss and introduced predators on Mauritius, Seychelles, and Rodrigues, respectively. Foudia rubra may be Critically Endangered, whereas F. sechellarum and F. flavicans are currently regarded as Vulnerable. The Asian yellow weaver (Ploceus megarhynchus) is a grassland species with a restricted range in India. Although the Asian golden weaver (Ploceus hypoxanthus) occurs in several countries, it is uncommon and regarded as Near Threatened.

On mainland Africa, the golden-naped weaver (P. aureonucha) and the yellow-footed weaver (P. flavipes) are both known only from the Ituri Forest, and have been seen just a few times in the last 30 years. Their canopy habitat and the political problems in this region make it difficult to obtain accurate information. Four localized species in West Africa, Bannerman's weaver (P. bannermani), Bates's weaver (P. batesi), the Gola malimbe (Malimbus ballmanni) and the Ibadan malimbe (M. ibadanensis), occur in forest that is disappearing rapidly throughout this region. The situation is most critical for the Ibadan malimbe, which has the smallest range. Two little-known species, the Loango weaver (P. subpersonatus) on the coastal strip and the black-chinned weaver (P. nigrimentum) in open savanna, range from Gabon southwards towards Angola.

In East Africa, Clarke's weaver (P. golandi) is restricted to the Arabuko-Sokoke Forest in Kenya, while the Tanzanian mountain weaver (P. nicolli) is found in relict forest patches on the Usambara Mountains and a few other sites. Fortunately both areas are now the site of active conservation programs. Agricultural changes in the highland grasslands of Kenya are a potential threat to Jackson's widow, while Fox's weaver (P. spekeoides) is apparently confined to one lake system in central Uganda, but remains unstudied. The Kilombero weaver (P. burnieri) was a surprising discovery in Tanzania, described in 1990 and evidently limited to a small area.

Significance to humans

Several colonial weaver species are closely associated with human settlements, nesting in exotic vegetation, and in forested areas, taking advantage of habitat changes to colonize new clearings. Eggs and nestlings may be utilized for food on occasion, but often the relationship is quite harmonious. The long tail feathers of breeding male long-tailed widows (Euplectes progne) were once used as elements in traditional head-dresses for warrior tribes in South Africa, but otherwise the colored plumages have not been utilized.

For hundreds of years, grain-eating weavers have been a pest for farmers in Africa. M. Adanson, a French botanist for whom the baobab genus Adansonia is named, spent several years in Senegal from 1747, and reported that the inhabitants suffered greatly from the depredations of the weavers. He described several traditional bird-scaring methods which are still in use in Africa today. Since the 1960s the red-billed quelea has been recognized as the major pest of cultivated cereals in Africa. Despite international efforts to reduce its numbers, using aerial spraying and fire-bombs set under roost sites, it remains enormously abundant: in March 2000 the South African department of agriculture reported that an estimated 21 million queleas had been killed in control operations during the past month! It seems that in the past, queleas bred prolifically in good years, and then starved when food supplies declined. Today when wild grass seeds are unavailable, they find crops a very acceptable alternative and consequently agriculture enables them to maintain high population levels. To the interested naturalist, a vast flock of queleas "roller-feeding" (in constant motion, with the birds at the back flying up over those ahead of them to be first at the untouched plants) is one of the great spectacles of Africa, but it is a catastrophe for the small farmer, and there is no simple, effective solution.

Species accounts

Resources

Ali, Salim, and S. Dillon Ripley. Handbook of the Birds of India and Pakistan, Together with Those of Bangladesh, Nepal, Bhutan and Sri Lanka. Vol. 10, Flowerpeckers to Buntings. Delhi: Oxford University Press, 1987.

Bruggers, Richard D., Clive C. H. Elliott. Quelea quelea Africa's Bird Pest. Oxford: Oxford University Press, 1999.

Craig, Adrian J. F. K. "Weaving A Story: The Relationships of the Endemic Ploceidae of Madagascar." In Proceedings of the 22nd International Ornithological Congress, edited by Nigel J. Adams and Robert H. Slotow. Johannesburg: BirdLife South Africa, 1984: 3063–3070.

Fishpool, Lincoln D. C., and Michael I. Evans. Important Bird Areas for Africa and Associated Islands: Priority Sites for Conservation. Newbury and Cambridge, United Kingdom: Pisces Publications and BirdLife International, 2001.

Fry, C. Hilary, Stuart Keith, and Emil K. Urban. The Birds of Africa. Vol. VII. London: Academic Press, in press.

Goodman, Steven M., and John P. Benstead. The Natural History of Madagascar. Chicago: University of Chicago Press, in press.

Sibley, Charles G., and Jon E. Ahlquist. Phylogeny and Classification of Birds. New Haven and London: Yale University Press, 1990.

Stattersfield, Alison J., and David R. Capper. Threatened Birds of the World: The Official Source for Birds on the IUCN Red List. Barcelona and Cambridge: BirdLife International/Lynx Edicions, 2000.

Andersson, Staffan. "Bowers on the Savanna: Display Courts and Mate Choice in a Lekking Widowbird." Behavioral Ecology 2 (1991): 210–218.

Barnard, Phoebe. "Territoriality and the Determinants of Male Mating Success in Southern African Whydahs (Vidua)." Ostrich 60 (1989): 103–117.

Brosset, Andre. "Social Organization and Nest Building in the Forest Weaver Birds of the Genus Malimbus (Ploceinae)." Ibis 120 (1987): 27–37.

Collias, Nicholas E., and Elsie C. Collias. "Evolution of Nest-Building Behavior in the Weaverbirds (Ploceidae)." University of California Publications in Zoology 73 (1964): 1–162.

Crook, John H. "The Evolution of Social Organisation and Visual Communication in the Weaverbirds (Ploceinae)." Behaviour Supplement 10 (1964): 1–178.

Hudgens, Brian R. "Nest Predation Avoidance by the Blue-Billed Malimbe Malimbus nitens (Ploceinae)." Ibis 139 (1997): 692–694.

Nicolai, Jürgen. "Der Brutparasitismus der Viduinae als ethologisches Problem." Zeitschrift für Tierpsychologie 21 (1964): 129–204.

Payne, Robert B. "Brood Parasitism in Birds: Strangers in the Nest." Bioscience 48 (1998): 377–386.

Winterbottom, M., T. Burke, and T. R. Birkhead. "The Phalloid Organ, Orgasm and Sperm Competition in a Polygynandrous Bird: The Red-Billed Buffalo Weaver (Bubalornis niger)." Behavioural Ecology and Sociobiology 50 (2001): 474–482.

[Article by: Adrian Craig, PhD]