A COMPARATIVE ANALYSIS OF NEST STRUCTURE IN THE WEAVER BIRDS (PLOCEINAE)

Abstract

Summary.Ploceine nests are small globes with entrances at the side or below, with or without some extension into a spout or tube. The fabric of the nest is often remarkably strong and pliant.Nine main variables of structure and construction in the nests of 62 species are listed and discussed. The paper includes the first account of the remarkable nest construction behaviour of Malimbus rubriceps in which nest material is “prepared” for use in building before the bird takes it to the nest.Correlations are found between nest shape, materials used in construction, methods of attachment, stitching and fabric, and nest‐sites. The correlations reveal four fundamentally different modes (A‐D) of structural organization, divisible into nest‐types specialized to particular sites. A classification is provided.The survival values of nest characteristics are analysed in relation to weather, predation and inter‐individual competition for materials. Fabric and lining are considered products of environmental selection, the stronger fabrics occurring in sites imposing greater stress. The roofing layer (which is correlated with tube loss) of many African colonial savannah birds is an adaptation to rain shedding. An alternative adaptation to rain occurs in Ploceus philippinus in India and consists in thickening the nest wall by excessive stitching on the exterior throughout nest occupation. This also correlates with the remarkable abilities of the species to repair its nest, in part an adaptation to the stealing of nest materials by neighbours.The direction of evolutionary change in nest structure is considered. Shifts in type of nest‐site expose the structure to new interactions with environment and predation to which the resultant nest is an adaptive compromise. Discussion of the range of nests as a whole is complicated by cases of convergence and ignorance concerning the precise origin of the sub‐family. In general the strong fabric and suspended nest mark a major advance on the simple structure found in other Ploceidae. These features allow the adoption of sites providing additional security from predators. Modes A and D are held to be primitive; but while A has proved adaptable to many environmental circumstances and has given rise not only to four nest‐types but also to both Modes B and C., Mode D occurs only in a small group of birds successful within a restricted niche in Africa.