The nest building behaviour and repair abilities of weaver birds (Ploceinae) constructing nests of two contrasting types are compared and experiments described. Ploceus philippinus builds a retort-shaped nest with a long tubular entrance. This structure is main-tained throughout occupation by wall thickening and tube lengthening. Repairs to extensive damage are quickly made and certain aberrant repairs throw light on the nature of normal construction. The nests of P. melanocephalus and relatives differ in that a roofing layer is inserted, the tube is not developed and the nest is not effectively repaired after occupation.
The two types of construction differ primarily in the relative extent of inhibition of building that follows the performance of cortain activities in the course of construction. Thus in melanocephulw the insortion of the roofing layer appears to inhibit work on the outer basket and entrance. There is however some evidence that perception of the species characteristic nest also brings work to an end. In philippinns by contrast the inhibiting effects of lining do not arise, building and rcpnir continue until factors, apparently internal, terminate construction behaviour when the young are well developed in the nest. The adaptive significance of these contrasts is discussed. They comprise alternative adaptations to very similar conditions of nesting in tropical Asia and Africa.