Sunday, November 10, 2002		Nature

The rigours of making a nest
Nutan Shukla

IN village weaverbirds, sparrow-sized birds, males build home, but the female rears the offspring. And while the female incubates the eggs, the male may try to attract another partner.

The male’s success in getting any female at all depends on his physical fitness and the quality of the nest he builds. Breeding takes place in the rainy season when there is plenty of new grass around for building and lots of insects for feeding the young. The male bird weaves the outer shell of a nest hanging from the tip of a branch, and whenever an unmated female visits the tree in search of a partner, he hangs from the nest by his feet, fluttering and showing off the bright colours under his wings.

If his display is adequate, and his nest is suitably fresh and green, the female may accept him. But she will refuse him, however good his display, if his nest is brown and dry. A nest turns brown in a week as the grass dries in the hot sun, so if a male does not attract a female while the nest is still green, he has to dismantle it and start again with fresh leaves. Only by insisting on a green nest can a female be certain it is newly built and strong enough to house her and her family.

Nest building is a very tedious exercise. A forked twig is all the support that this bird needs for building nest. Once a male has chosen a site, he collects building materials such as strips of leaves, vines and tall grasses, then knots the strips to his twig using only his beak and feet. In this way he makes a firm grass ring — the foundation of his nest.

Gradually, this African bird builds up a roof and walls by knotting and threading strips over and under one another with his beak. Next he adds a porch, curving it down over the front of the nest. The final shape is rather like a snail shell with the entrance underneath. A threshold between the porch and the egg chamber keeps eggs and chicks from rolling out of the nest.

It may take up to a week for the male weaverbird to complete a nest. Once he has finished weaving, he hangs beneath the nest and flutters his wings to attract the attention of a female.

Usually, a young male weaverbird’s first attempts at weaving a nest are rather untidy, and he may have to build several nests before he can persuade a female to mate and lay her eggs in one. If he is unlucky he has to start again. With practice, however, his efforts get much neater. Once a female has accepted a nest, she lines the egg chamber with soft grass tips and feathers before laying her clutch of three or four eggs, which she incubates for about two weeks.

An underside entrance makes it difficult for larger birds to get into a weaverbird’s nest and steal eggs or chicks.

Asian bays weaverbirds, also found in India, and African cassin’s weavers build a sleeve-like entrance tunnel about 2 ft long that collapses inwards if a bird of prey attacks it. To enter the nest itself, a weaverbird swoops down at speed to the tunnel entrance and then folds its wings, allowing its momentum to carry it upward through the tunnel without touching the sides.