At
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
detail. 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.