Nest building by birds

Abstract

What is a bird nest like? Bird nests vary enormously among species in their form, size and composition. The nest of a long-tailed tit (Aegithalos caudatus) is a flexible bag composed of small-leaved mosses entangled in myriad loops of fluffy spider egg cocoon silk - a 'Velcro' fabric. For insulation, this bag is lined with as many as 2,000 small feathers. For camouflage, the outside of the nest is covered with a few thousand small lichen flakes. At the other extreme of nest complexity is the nest of the Arctic tern (Sterna paradisea), which is often no more than a shallow depression scraped in a shingle beach. The size of nests is equally variable. An Antillean crested hummingbird (Orthorhyncus cristatus), at ∼2.4 grams, may be more than twice the weight of the tiny nest cup on which it sits, while the massive platform nest of the bald eagle (Haliaeetus leucocephalus) can be three metres in width and weigh up to three metric tons, about 600 times the weight of the bird itself. The composition of nesting material varies from grasses and twigs to those used by the common tailorbird (Orthotomus sutorius), which stitches together a folded-over living leaf with threads of spider silk.