Geoscience Reference
In-Depth Information
Examples of scrape nests are those of penguins or some shorebirds, such as oyster-
catchers (species of
Haematopus
) or plovers (mostly species of
Pluvialis
and
Charadrius
), which use their feet to scratch out slight depressions into which they
deposit a few eggs. Among the latter are the massive individual nests of bald eagles
(
Haliaeetus leucocephalus
), as well as the communal nests of the sparrow-sized so-
ciable weaver birds (
Philetairus socius
). The largest bald-eagle nest yet measured
was3m(10ft)wide,6m(20ft)deep,andweighedmorethantwotons.Thesenests
are usually constructed in trees sturdy enough to hold such nests or on the tops of
rocky cliffs. Sociable weaver nests of South Africa are among the most spectacular
of all avian-made traces. Unlike the individual typical cup- or saucer-shaped nests
peoplemaynormallyseeinurbansettings,thesenestsaremadecollectively,shared,
andreusedbyhundredsofweaverbirds.Placedinstouttreesorontelephonepoles,
weavernestsarecomposedofmultiple chambers andentrances, areasmuchas3to
7 m (10-23 ft) in outline, and are used for both nesting and shelter by non-nesting
adults. They are so massive, other bird species nest in or on them.
Nottobeoutdone,themalleefowl(
Leipoa ocellata
)ofAustraliaconstructsgi-
gantic incubation mounds for its eggs. These mounds can be as much as 4 m (13 ft)
tall and 10 m (33 ft) wide, representing the movement of more than 200 m
3
(7,000
ft
3
) of soil. For incubation, the parents let anaerobic bacteria do all of the work for
them, breaking down organic material in the mounds and generating enough heat
to keep the eggs toasty. In short, birds can make modest nests, incredible nests, and
everything in between.
Although bird nests are almost as diverse as birds themselves, they can be
placedintoeightbasickinds,basedonwheretheyarelocatedortheiroverallshape:
scrape, platform, crevice, cup (or saucer), spherical, pendant, cavity, burrow, and
mound. Of these, probably the one most people see are cup nests in trees, in which
various songbirds arranged sticks or other vegetative debris—perhaps cemented by
mud, bird spit, or feces—into a semi-circular bowl that keeps eggs from falling out.
