Like
a carton for store-bought eggs, nest materials help to
cushion, insulate, and keep the clutch together. These
materials may be of little importance for birds such as
terns and murres, which require little more than a resting
spot for their eggs. In contrast, nest materials can be
critical for some species -- as in the case of Bald Eagles,
whose young require a durable playpen that an adult pair may
maintain for decades. An important function of
nest materials gathered by ground-nesting precocial birds is
to prevent their eggs from becoming embedded in sand or mud
after heavy rains or flooding due to exceptionally high
tides. Often only enough material is collected to create a
buffer that raises the eggs off the substrate. Such a buffer
also helps to guard against cracking when the eggs are
rotated for uniform heating during incubation. In the case
of many marsh-dwelling birds, the buffering layer may be
expanded to form sides and sometimes extended to create a
relatively fragile canopy, helping to hide the
site. Because the form of the nest
varies from habitat to habitat, and must be adapted to fit a
bewildering diversity of supporting structures, it is not
surprising that an almost limitless variety of materials
(including stones and mud, animal and plant products, and
human-made artifacts) have at one time or another been
incorporated into nests. Avian products that become part of
nests include saliva (the main ingredient in cave swiftlet
nests used in Chinese "bird's nest" soup), ejected pellets,
feathers, down, and guano. Feathers are highly valued, in
part because of their capacity to trap air and provide
insulation. Products of other animal species may include
silk from cocoons and spider webs, cast snake skins, hair,
fur, bits of cow pats, shells, etc. The variety of plant and
manufactured products found in nests is enormous, including
virtually anything that can be carried. Some adhesive materials are
required to bind and to provide support in adherent and
hanging nests. Such materials include mud (swallows), saliva
(swifts), caterpillar silk (hummingbirds, vireos), certain
plant fibers, and leaf mold (Wood Thrushes). These binding
materials can be remarkably durable. For example, cellulose,
the major constituent of plant fibers, is waterproof and,
ounce for ounce, stronger than steel. Other water-shedding
substances used in nests include lichens and spider
webs. Some materials are selected
specifically to help sanitize the nest. More than half of
our hawk species routinely add fresh green leaves that
contain natural pesticides such as hydrocyanic acid, which
may inhibit infestation by insect parasites. Such preventive
efforts are not limited to birds of prey. Users of old nest
sites, such as starlings, can discriminate between helpful
and ornamental leaves and select those that deter lice and
bacteria for inclusion in their nests. Avian ingenuity is seemingly
boundless. For example, the Great Kiskadee is known to add
the entire nest of the Vermilion Flycatcher to its own,
presumably to increase its cushioning/insulating properties.
Lists of nesting materials published by early ornithologists
provide a sort of fossil record allowing us to trace
changing patterns of use. Comparison of these records with
contemporary observations of nest materials helps to
document changes in the availability of materials. For
instance, the Chipping Sparrow, at the turn of the century,
was commonly referred to as the "hairbird" from its practice
of lining its nest with horse hair. With the advent of
mechanized travel and the decline of horses, both the trait
and the name disappeared. Similarly, a number of
contemporary inventions such as plastic insulation and
cellophane may substitute for snake skin in nests of some
flycatchers and titmice or replace other once common
materials. Thus, nests used perennially could serve as
storehouses of data. A White Stork nest still in use in 1930
dated to 1549. One 36-year-old nest of a Bald Eagle, which
finally collapsed along with its supporting tree in a storm,
contained two tons of accumulated material. Dissection of
either nest could have proved a fascinating (if messy)
enterprise. SEE: Nest
Lining;
Masterbuilders;
Disease
and Parasitism;
Eggs
and Their Evolution;
Incubation:
Heating Eggs;
Precocial
and Altricial Young. Copyright
® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl
Wheye.