Weavers
Weavers
Weavers are a relatively large family of 135 species of perching birds, comprising the family Ploceidae. Weavers are native to Africa, Madagascar, Eurasia,
and Malaysia. This group is richest in species in Africa. However, some species have been widely introduced outside of their natural range.
Species of weavers occur in a wide range of terrestrial habitats, including semi-deserts, grasslands, savannas, and various types of forests. They do not migrate, although during times of drought and food shortage, they may undertake wanderings covering hundreds of miles (kilometers).
Weavers are relatively small birds, most with a body length of 3.9-9.8 in (10-25 cm)—not including the very long tail of some African species. They are rather stout-bodied, and have short, pointed, conical, seed-eating bills. The coloration and patterns of their plumage are highly variable among species, and are quite attractive in some cases.
Weavers mostly eat seeds, but they also eat other small fruits, succulent foliage, and insects.
Most species of weavers are gregarious, occurring in flocks during the nonbreeding season, and often nesting in colonial groups. Their calls are harsh and repeated chirps, buzzes, and chattering, and not very musical.
Nesting and breeding systems are extremely variable among the weavers. Nesting strategies range from large, woven colonial nests to individually woven nests. Some species are polygynous, in which a male breeds with as many females as possible, and helps little with the incubation of eggs or care of the young birds. One species, the cuckoo weaver (Anomalospiza imberbis ), is a parasitic breeder, laying its eggs in the nests of other species, which then raise the parasitic baby. In most species, however, a one-family domed nest is constructed, the clutch size is two to eight, the female or both sexes incubate the eggs, and both parents care for the young.
Species of weavers
The typical weavers are in the genus Ploceus. The village weaver (Ploceus cucullatus ) of African savannas is a colonial nester, with many pairs of birds building individual, pendulous nests from the same tree. The social weaver (Philetairus socius ) is also a colonial nester. However, this species builds an aggregate, apartment-like nest, comprised of large numbers of arboreal hanging nests constructed immediately adjacent to each other, so that the finished mass looks rather like a haystack. The entrance holes to the individual compartments are on the underside of the mass, so that entry requires a brief hover.
One of the most spectacular weavers is the paradise widowbird or whydah (Steganura paradisea ), which breeds in savannas of tropical Africa. Males of this polygynous species achieve a length of 13.4 in (34 cm), of which about three-quarters is due to their fabulously long tail, comprised of three or four over-developed, black feathers. This attractive bird also has a black face and back, a chestnut breast, a yellow nape, and a whitish belly. Female paradise widowbirds are relatively drab, brownish-and-whitish birds.
Field studies have shown that paradise widowbird males with the longest tail are more successful in attracting females. In part, this was demonstrated by clipping the tail of some individuals. These truncated fellows were then considerably less fortunate in their love life than males who had not been tampered with, or had their tail cut, and then glued back on. This is an example of sexual selection, in which traits that may be detrimental in some respects, for example, in foraging or escaping from predators, may nevertheless be selected for because they enhance reproductive success. In this case, the extraordinarily long tail of male paradise weaverbirds is favored by sexual selection, because a long tail has an irresistible appeal to females.
Some other weavers also have long tails, for example, the queen whydah (Vidua regia ), and the pin-tailed weaverbird (Vidua macroura ), both of tropical Africa.
KEY TERMS
Polygyny —A breeding system in which a male attempts to breed with as many females as possible. In avian polygyny, the female usually incubates the eggs and raises the babies.
Sexual selection —This is a type of natural selection in which anatomical or behavioral traits may be favored because they confer some advantage in courtship or another aspect of breeding. For example, the bright coloration, long tail, and elaborate displays of male pheasants have resulted from sexual selection by females, who apparently favor extreme expressions of these traits in their mates.
Conflicts with humans
Some species of weavers occur in large numbers in urban and agricultural areas, where for various reasons they may be regarded as pests. The house sparrow and the Eurasian tree sparrow are most important in this respect. The world’s most important avian pest is probably the quelea (Quelea quelea ) of Africa, which eats large quantities of ripe grains in places where it is abundant. This bird roosts communally in huge numbers, where it is sometimes sprayed with an organophosphate pesticide. It has been estimated that as many as one billion of these weavers are killed in this way each year.
See also Finches.
Resources
BOOKS
Bruggers, Richard D., and Clive C.H. Elliott. Quelea quelea: Africa’s Bird Pest. New York: Oxford University Press, 1990.
Bill Freedman