Why is the pensile loxia of the Cape and Madagascar so called?

Because it builds a remarkable nest, in the vicinity of water, in shape almost like a retort, with a depending neck for ingress and egress, and so disposed that the aperture is close to the water. - Blumenbach.

Why do many birds of warm climates build pendulous nests, which are attached to the extreme branches of trees?

Because there only are they secure from their enemies, the snakes and monkeys.