The Sociable Weaver Philetairus socius is a cryptically coloured passerine about 14 cm in length, weighing about 27 g and living in a semi-arid to arid region of southwestern Africa. Its range coincides with that of stout trees like Acacia giraffae, and of stiff dry grasses like Aristida ciliata; these plants provide nest sites and building material respectively. A colony of Sociable Weavers may number from two birds to over 500 birds and may occupy a single large nest mass, several nest masses in one tree, or several nest masses in two or more adjacent trees. In the study area in the Kalahari Gemsbok National Park, the density of Sociable Weavers was about 80 birds/km during the 19-month study period. Neighbouring colonies may be as little as 0,8 km apart, but are usually further apart than this, so that the density of colonies is not directly proportional to the density of trees. Intercolonial movements are rare. The study period was too short for a definitive population study of the Sociable Weaver.