How do birds make their nest just the right shape?
A. Many birds construct their nest from the inside, shaping it with their body. Female American Robins plaster grasses, small twigs, and other fibers together with mud. As they build, they frequently rotate their body within the growing structure to smooth and shape it. The Baltimore Oriole clings to the supporting twig, often head down, and while holding a fiber makes rapid thrust-and-draw movements with her mandibles. Once she’s woven a small section, she starts clinging to it, and ends up working from the inside as the nest is completed. She doesn’t appear to specifically tie knots, and the stitching of a closely-examined nest appears to be random, but the end result is a tightly woven structure. Imagine doing all that with just your mouth!
