Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [23]
White-faced hornet nest with two wasps adding paper to the bottom edge of the outermost sheet.
As the wasp family grows and more room is needed, the insects enlarge their nest by recycling the paper walls from the inside to make new, larger ones on the outside. A nest starts out in May no bigger than a walnut with just one paper shell, and ends up basketball-size by late summer having about a dozen layers of paper insulation surrounding almost as many horizontal combs with pupae and larvae, hanging one above the other inside. Each air layer between successive sheets of paper acts as insulation, and the temperatures inside the nest stay between 29° and 31°C even in cold weather down to 5°C, as the wasps shiver with their muscles powering their wings to maintain their own body temperature above 40°C. The heat loss from the body then heats the nest and young.
We are recognizably humans for only about 3 million years, but definitive birds have been flying well over 100 million years. At first their nests were, like those of their reptilian ancestors, simply depressions scraped in the ground or hiding places for their eggs and/or young. As birds became ever more metabolically active, in part to become creatures capable of rapid and sustained flight, they at the same time became warm-blooded and the ability to produce heat ended up being not just an option but a necessity both for them and their young. Expanding northward or into seasonal environments then generated selective pressure for their nests not only to be receptacles for their eggs and young, but also warm shelters.
The nests of northern and late-winter nesting birds, such as gray jays, raven, crossbills, and golden-crowned kinglets, are superbly insulated structures that are essential for these birds’ lives in their respective environments; the eggs and young must be kept warm, while minimizing heating costs.
The golden-crowned kinglet’s nests are built by suspending strands of spiderwebs, bark strips, and caterpillar silk into a hammocklike configuration within the hanging twigs of a spruce or fir. Moss, lichens, and strips of paper birch bark are then incorporated into the bottom and wall of the nest. The resulting cup-shaped structure is suspended into twigs by its lips and its walls. It is insulated with snowshoe hare down and with small bird feathers, numbering 2, 486, 2, 674, and 2, 672 feathers in three nests where individual feather counts were made (Thaler 1990, pp. 83–84). The nests are hidden from view from above, and partially protected from rain and sun by overhanging twigs of spruce or fir. However, regardless of how elaborate, almost all bird nests are built for only one-time use, and a good time to find many of these discarded nests is in the winter.
Bird nests are records of genetically encoded behaviors. Each bird performs unlearned nest-construction behavior, duplicating fairly precisely what its parents had done. Some nest-construction behaviors are relatively simple. Geese, for example, pick an appropriate nest location, and then simply lay their eggs there. Often the female pulls in nearby vegetation from all around and banks it against her body. She then sheds her belly feathers and tucks them under her for a nest lining. In the Canada geese I’ve watched in a bog by my house, this down-lining of the nest occurs only after or when the eggs are laid. (Reduction of the goose mother’s belly insulation could probably be hazardous when she swims in ice-cold water, but it may be necessary on the nest, so that body heat becomes available to the eggs she sits on.)
Most birds collect specific nest material from a wide area, and they execute specific behaviors both to find and work with it. Bicknell’s thrushes