first glance, a display of the materials birds have used to
line their nests might be linked to an avian pawnshop. On
closer scrutiny, however, these sometimes incongruous
substances can be grouped into five more or less discrete
classes: finer materials, feathers, concealing ornaments,
remnants, and artifacts. To save space in some species
treatments these terms may be used to label materials lining
the nests; here we describe them in greater
First, the lining may consist of loose, smaller bits of the same materials that have been incorporated into the latticework of the nest. These finer materials are utilized to shed water, deter pests, conceal the eggs from predators, insulate, and cushion them. Typically, finer materials are bits of vegetation (including leaves, needles, twigs, sticks, reeds, mosses, lichen, grass, seaweed, etc.), but birds may also take advantage of a variety of other readily available and portable animal products such as hair, fur, or shreds of dry cow pats.
The second lining material, feathers (including down), usually comes from the brooding birds themselves, but those of other species may be gathered, as well. They also serve to insulate and cushion the eggs.
A third type of lining, often found in the minimal scrapes made by ground nesters, consists of concealing ornaments -- collections of nearby objects whose main value lies in providing camouflage for otherwise exposed eggs. In some situations they may help to keep the eggs in place, provide additional insulation, or prevent the eggs from becoming embedded in mud or sand after inadvertent flooding of the nest. These objects include stones, rock shards, shells, bits of wood, moss, lichen, withered leaves, or nearby grasses that sometimes may be simply plucked by the incubating adult as it sits.
A fourth type, remnants, is material that has not been placed deliberately in the nests by the birds. Wood chips found in the arboreal excavations of cavity-nesting species, the remains from the winter nests of squirrels and mice occasionally found in tunnels and chambers of burrow-nesting species, bits of vegetation deposited by wind, and pieces of surrounding plants broken as ground-nesting adults mat down the vegetation to form their depression-like nest are a few of the many items coincidentally cradling eggs. In simple scrapes some remnants may function as concealing ornaments as well.
A fifth lining type, artifacts, includes a vast array of manufactured or natural, shiny, eye-catching objects. These materials are sometimes poorly suited for use in a nest, and their choice by adults is perplexing. In one study of Wrynecks (Jynx torquilla a distinctive member of the woodpecker family), the stomachs of 4 out of 14 young that had died in their nests were found to contain a potentially lethal shiny stone or piece of glass. Why the adults included such items in their nests is unknown. Certainly the ingested artifacts did not serve to supplement the diet of the young. If their presence illustrates nothing more than a misguided attraction that some birds have for adding dangerous materials to their nests, one wonders why natural selection has not operated more strongly against such behavior.
If by default or by design, the nest or incubation site has no lining, then eggs simply rest directly on the substrate or on the supporting nest lattice. Such nests or sites are described as unlined and are typical of a number of colonial cliff-nesting birds.
SEE: Nest Materials; Masterbuilders; Eggs and Their Evolution; Incubation: Heating Eggs; Feathered Nests; Brood Patches.
Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.