Sociable Weavers’ enormous nests are characteristic sights of the Kalahari. Built from twigs, sticks and grass, the nests consist of numerous tunnels ending in nest chambers. Large nests are inhabited by up to 500 birds. The nests act as effective insulators against cold and heat; research has shown that temperatures in the chambers are 2 to 3 °C lower than outside temperatures during the day, but up to 8 °C warmer at night. Four or five birds often roost together in a chamber to keep warm during cold winter nights, but in summer chambers are occupied by only two birds.