Answer: kin selection
Explanation: the sociable weavers are a species of birds in the weaver family found in southern Africa. Their unique feature is that they build large communal nests which may house over 100pairs, some with nestlings. It is arguably one of the most impressive structures constructed by any bird species. The cooperation exhibited in nest building has been linked to kin selection.
Kin selection is an evolutionary tactic which guarantees the survival of a species even at the expense of each individual's survival or reproduction. In colonies such as that of sociable weavers, social cooperation may replace kin recognition and the same principle applies. The weavers act as a collective unit and each nest may serve several generations of birds.