Did you know?
Pygmy falcons are frequent squatters in sociable weaver nests, and refrain from eating their hosts – usually.
If a sociable weaver came and sat a metre away, you’d hardly pay it a 2nd glance. This inconspicuous brown, grey and black bird lives in the arid, sandy Kalahari and twitters cheerfully all day long.
Its nest, however, can make your jaw drop in amazement. Looking like haystacks planted in quiver trees, thorn trees, windmills or on telephone poles, these communal nests are crucial to the birds’ survival.
They are also testament to what teamwork can do. Each of these gigantic nests is home to around 300 of these small birds. Every bird adds a few more bits of grass and straw to the nest every day.
The results are staggering. A single nest can weigh more than 1 000 kilograms. Not surprisingly, the trees or structures in which they are built sometimes just collapse.
Undaunted, the sociable weavers immediately start on their next building project.
What makes them do it? The Kalahari is a semi-desert, with extreme temperatures. On a winter’s night, the mercury can plummet well below freezing. At noon in the height of summer, it's so hot that heat mirages form on the horizon.
The sociable weavers' grassy, thatched, insulated home, however, allows the birds to live at fairly moderate temperatures. Small animals like these (sociable weavers weigh only about 27 grams) are very prone to heat stress and if it weren’t for their nests, they would have to expend great amounts of energy obtaining more water and regulating body temperature.
Their habits also help. Sensibly, they retire to their various nest chambers for a siesta in the heat of a summer’s day.
And on chilly winter’s nights, the birds huddle up, sometimes 5 to a chamber. In this way, they can save up to 50% of the energy they would have had to expend in keeping warm.