Sunday, October 27, 2002		Nature

Male weaverbirds make nests to attract females
Nutan Shukla

WEAVERBIRDS are artists par excellence in weaving out intricate nests of grass that no one, not even humans, can imitate. No bird is more adept at building nest by twisting and making loops of strips of leaves to make a roofed hanging basket — a structure which is held together not by any adhesive, but by simple frictional resistance of the material.

If we observe the nest, we will find that it is not woven. Instead, it is an example of fine needle work. Weaving is a rather misleading term in the context of these nests which have irregular arrangements of strands. The most astonishing fact is that these birds, in the process of building nests, carry out a variety of clear-cut ‘stitches’ which include complicated interlocking loops, alternately reversed winding, spiral winding, overhand and slip knots. For the purpose, birds tear strips of grass and palm leaves from living green plants because the above control over building material can not be achieved with dried strips which become quite hard.

It is the male weaverbird that constructs nests and then tries to attract females to mate and lay eggs there. While weaving out a nest, the male adds each new strip of vegetation by pushing it into the fabric, pulling through, pushing it in again, and so on, much more like needlework than weaving.

If these structures are inspected closely it can be easily understood that the nest-building behaviour is not entirely hereditary, instead it is at least partially learned. It has been seen that the first nest constructed by a young male is usually very rough looking and the technique too is not as perfect as that of an experienced male.

Another, very interesting fact about the bird is that the males are perfectionists in the real sense as far as nest-building is concerned. Perhaps, the reason is that females can only be attracted by building perfect nests, hence males are very sensitive about them. If a bird’s routine is disrupted by the destruction of a part of the nest it has just completed, instead of simply repairing the damage, it tears the whole nest to pieces and starts afresh.

Weavers’ nests are a fortress for the young where they are extremely well protected from the predators. These nests are usually situated high in trees, well out of reach of ground animals. Also, the nests are often placed at the ends of thin twigs or palm fronds, where large and heavy animals cannot climb. To provide further security nests are sometimes built on branches overhanging ponds or rivers.

Classified under the family ploceidae along with sparrows, there is one group of 94 species of ‘true’ weavers. Other types of weavers include bishops, that build globular nests in grasses or bushes.

Viduine weavers and whydahs, belonging to another group, are ‘brood parasites’, like cuckoos. They do not build their own nests, instead lay their eggs in the nests of waxbills whose chicks have coloured marks in their mouth that stimulate the parents to feed when the mouth is opened. Whydah chicks too have coloured marks in their mouths, which help them in deciding their foster parents.

Three species of buffalo weavers make the third group of these birds (bubalornithinae). Found in south of the Sahara Desert in Africa, they make large, untidy, domed nests of thorny twigs.

Thirtyseven species of sparrows constitute the fourth group, which include rock sparrows, snow finches and the tree sparrows. The name ‘sparrow’ itself is very confusing as in the case of finches. It is often given to any small bird with a short, thick bill, a characteristic of seed-eaters, and streaked plumage with shades of brown, grey and black. To avoid confusion, the only way is to use the scientific (Latin) name for the species.